TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Zakharov, Alexander F.
PY  - 2024
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/13024
AB  - Here we study possible improvements of the existing constraints on the upper bound of the graviton mass by the analysis of the stellar orbits around the supermassive black hole (SMBH) at the Galactic Center (GC) in the framework of Yukawa gravity. A motivation for this study is a recent detection of Schwarzschild precession in the orbit of S2 star around the SMBH at the GC by the GRAVITY Collaboration. The authors indicated that the orbital precession of the S2 star is close to the general relativity (GR) prediction, but with possible small deviation from it, and parametrized this effect by introducing an ad hoc factor in the parametrized post-Newtonian (PPN) equations of motion. Here we use the value of this factor presented by GRAVITY in order to perform two-body simulations of the stellar orbits in massive gravity using equations of motion in the modified PPN formalism, as well as to constrain the range of massive interaction Λ. From the obtained values of Λ, and assuming that it corresponds to the Compton wavelength of graviton, we then calculated new estimates for the upper bound of graviton mass which are found to be independent, but consistent with the LIGO’s estimate of graviton mass from the first gravitational wave (GW) signal GW150914 (later this graviton mass estimation was significantly improved with consequent observations of GW events). We also performed calculations including numerical simulations in order to constrain the bounds on graviton mass in the case of a small deviation of the stellar orbits from the corresponding GR predictions and showed that our method could further improve previous estimates for the upper bounds on the graviton mass. It is also demonstrated that such an analysis of the observed orbits of S-stars around the GC in the frame of the Yukawa gravity represents a tool for constraining the upper bound for the graviton mass, as well as for probing the predictions of GR or other gravity theories.
T2  - Physical Review D
T1  - Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center
VL  - 109
IS  - 6
SP  - 064046
DO  - 10.1103/PhysRevD.109.064046
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Zakharov, Alexander F.",
year = "2024",
abstract = "Here we study possible improvements of the existing constraints on the upper bound of the graviton mass by the analysis of the stellar orbits around the supermassive black hole (SMBH) at the Galactic Center (GC) in the framework of Yukawa gravity. A motivation for this study is a recent detection of Schwarzschild precession in the orbit of S2 star around the SMBH at the GC by the GRAVITY Collaboration. The authors indicated that the orbital precession of the S2 star is close to the general relativity (GR) prediction, but with possible small deviation from it, and parametrized this effect by introducing an ad hoc factor in the parametrized post-Newtonian (PPN) equations of motion. Here we use the value of this factor presented by GRAVITY in order to perform two-body simulations of the stellar orbits in massive gravity using equations of motion in the modified PPN formalism, as well as to constrain the range of massive interaction Λ. From the obtained values of Λ, and assuming that it corresponds to the Compton wavelength of graviton, we then calculated new estimates for the upper bound of graviton mass which are found to be independent, but consistent with the LIGO’s estimate of graviton mass from the first gravitational wave (GW) signal GW150914 (later this graviton mass estimation was significantly improved with consequent observations of GW events). We also performed calculations including numerical simulations in order to constrain the bounds on graviton mass in the case of a small deviation of the stellar orbits from the corresponding GR predictions and showed that our method could further improve previous estimates for the upper bounds on the graviton mass. It is also demonstrated that such an analysis of the observed orbits of S-stars around the GC in the frame of the Yukawa gravity represents a tool for constraining the upper bound for the graviton mass, as well as for probing the predictions of GR or other gravity theories.",
journal = "Physical Review D",
title = "Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center",
volume = "109",
number = "6",
pages = "064046",
doi = "10.1103/PhysRevD.109.064046"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Zakharov, A. F.. (2024). Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center. in Physical Review D, 109(6), 064046.
https://doi.org/10.1103/PhysRevD.109.064046

Jovanović P, Borka Jovanović V, Borka D, Zakharov AF. Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center. in Physical Review D. 2024;109(6):064046.
doi:10.1103/PhysRevD.109.064046 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Zakharov, Alexander F., "Improvement of graviton mass constraints using GRAVITY’s detection of Schwarzschild precession in the orbit of S2 star around the Galactic Center" in Physical Review D, 109, no. 6 (2024):064046,
https://doi.org/10.1103/PhysRevD.109.064046 . .

TY  - JOUR
AU  - Lazarov, Nenad Đ.
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/11234
AB  - In our work we presented the modified field equations generated by action with unspecified function f (R). Assuming spherical symmetry, we used the corresponding static Schwarzschild-like metric in the weak field limit. Also we considered geodesic equations of motion describing orbits and orbital speeds which can be measured in galactic environment. We solved geodesic equations in the case of a power-law f (R) theories, that is we set f (R) = f0nRn.
T2  - Filomat
T1  - Geodesic equations in the weak field limit of general f (R) gravity theory
VL  - 37
IS  - 25
SP  - 8575
EP  - 8581
DO  - 10.2298/FIL2325575L
ER  - 

@article{
author = "Lazarov, Nenad Đ. and Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "In our work we presented the modified field equations generated by action with unspecified function f (R). Assuming spherical symmetry, we used the corresponding static Schwarzschild-like metric in the weak field limit. Also we considered geodesic equations of motion describing orbits and orbital speeds which can be measured in galactic environment. We solved geodesic equations in the case of a power-law f (R) theories, that is we set f (R) = f0nRn.",
journal = "Filomat",
title = "Geodesic equations in the weak field limit of general f (R) gravity theory",
volume = "37",
number = "25",
pages = "8575-8581",
doi = "10.2298/FIL2325575L"
}

Lazarov, N. Đ., Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Geodesic equations in the weak field limit of general f (R) gravity theory. in Filomat, 37(25), 8575-8581.
https://doi.org/10.2298/FIL2325575L

Lazarov NĐ, Borka Jovanović V, Borka D, Jovanović P. Geodesic equations in the weak field limit of general f (R) gravity theory. in Filomat. 2023;37(25):8575-8581.
doi:10.2298/FIL2325575L .

Lazarov, Nenad Đ., Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Geodesic equations in the weak field limit of general f (R) gravity theory" in Filomat, 37, no. 25 (2023):8575-8581,
https://doi.org/10.2298/FIL2325575L . .

TY  - JOUR
AU  - Borka-Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/12725
AB  - Here we investigate the giant radio galaxy DA 240, which is a FR II source. Specifically, we investigate its flux density, as well as the spectral index distribution. For that purpose, we used publicly available data for the source: Leahy's atlas of double radio-sources and NASA/IPAC Extragalactic Database (NED). We used observations at 326 MHz (92 cm) and at 608 MHz (49 cm) and obtained spectral index distributions between 326 and 608 MHz. For the first time we give spectral index map for these frequencies. We found that the synchrotron radiation is the dominant radiation mechanism over most of the area of DA 240, and also investigated the mechanism of radiation at some characteristic points, namely its core and the hotspots. The results of this study will be helpful for understanding the evolutionary process of the DA 240 radio source.
T2  - Contributions of the Astronomical Observatory Skalnaté Pleso
T1  - Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240
VL  - 53
IS  - 3
SP  - 188
EP  - 196
DO  - 10.31577/caosp.2023.53.3.188
ER  - 

@article{
author = "Borka-Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "Here we investigate the giant radio galaxy DA 240, which is a FR II source. Specifically, we investigate its flux density, as well as the spectral index distribution. For that purpose, we used publicly available data for the source: Leahy's atlas of double radio-sources and NASA/IPAC Extragalactic Database (NED). We used observations at 326 MHz (92 cm) and at 608 MHz (49 cm) and obtained spectral index distributions between 326 and 608 MHz. For the first time we give spectral index map for these frequencies. We found that the synchrotron radiation is the dominant radiation mechanism over most of the area of DA 240, and also investigated the mechanism of radiation at some characteristic points, namely its core and the hotspots. The results of this study will be helpful for understanding the evolutionary process of the DA 240 radio source.",
journal = "Contributions of the Astronomical Observatory Skalnaté Pleso",
title = "Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240",
volume = "53",
number = "3",
pages = "188-196",
doi = "10.31577/caosp.2023.53.3.188"
}

Borka-Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240. in Contributions of the Astronomical Observatory Skalnaté Pleso, 53(3), 188-196.
https://doi.org/10.31577/caosp.2023.53.3.188

Borka-Jovanović V, Borka D, Jovanović P. Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240. in Contributions of the Astronomical Observatory Skalnaté Pleso. 2023;53(3):188-196.
doi:10.31577/caosp.2023.53.3.188 .

Borka-Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Study of spectral index of giant radio galaxy from Leahy's Atlas: DA 240" in Contributions of the Astronomical Observatory Skalnaté Pleso, 53, no. 3 (2023):188-196,
https://doi.org/10.31577/caosp.2023.53.3.188 . .

TY  - CONF
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/11941
AB  - Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.
C3  - Proceedings of Science
T1  - Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84
VL  - 427
SP  - 193246
DO  - 10.22323/1.427.0043
ER  - 

@conference{
author = "Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2023",
abstract = "Here we study the flux densities distribution at 1380, 4908 and 15365 MHz, as well as the radio spectral index of 3C 84, a Double Radio source Associated with Galactic Nucleus (DRAGN). 3C 84 is the dominant giant elliptical galaxy in the Perseus cluster, and thus very interesting for our research. This famous radio galaxy Perseus A has Relaxed Double classification because it has the large halo, with the lack of its compact structure. We show its structure (using 2D and 3D flux density plot). Besides, we calculated the radio spectral index, which we then used to investigate the nature and mechanisms of its radiation. The obtained values of spectral indices indicated that the northern hotspot is dominated by synchrotron radiation, while in southern hotspot there are thermal and non-thermal radiations, depending on the studied frequency pairs.",
journal = "Proceedings of Science",
title = "Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84",
volume = "427",
pages = "193246",
doi = "10.22323/1.427.0043"
}

Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2023). Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84. in Proceedings of Science, 427, 193246.
https://doi.org/10.22323/1.427.0043

Borka Jovanović V, Borka D, Jovanović P. Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84. in Proceedings of Science. 2023;427:193246.
doi:10.22323/1.427.0043 .

Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Flux densities and spectral indices of Relaxed Double radio galaxy 3C 84" in Proceedings of Science, 427 (2023):193246,
https://doi.org/10.22323/1.427.0043 . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Zakharov, Alexander F.
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10849
AB  - In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction Λ and universal constant δ) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction [1]. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant δ, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction δ and find that this parameter has strong influence on range of Yukawa interaction Λ. For that purpose we use parameterized post-Newtonian (PPN) equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.
T2  - Journal of Cosmology and Astroparticle Physics
T1  - Constraints on Yukawa gravity parameters from observations of bright stars
IS  - 03
SP  - 056
DO  - 10.1088/1475-7516/2023/03/056
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Zakharov, Alexander F.",
year = "2023",
abstract = "In this paper we investigate a Yukawa gravity modification of the Newtonian gravitational potential in a weak field approximation. For that purpose we derived the corresponding equations of motion and used them to perform two-body simulations of the stellar orbits. In 2020 the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center (GC) and showed that it is close to the general relativity (GR) prediction. Using this observational fact, we evaluated parameters of the Yukawa gravity (the range of Yukawa interaction Λ and universal constant δ) with the Schwarzschild precession of the S-stars assuming that the observed values as indicated by the GRAVITY Collaboration will have a small deviation from GR prediction [1]. GR provides the most natural way to fit observational data for S-star orbits, however, their precessions can be fitted by Yukawa gravity. Our main goal was to study the possible influence of the strength of Yukawa interaction, i.e. the universal constant δ, on the precessions of S-star orbits. We analyze S-star orbits assuming different strength of Yukawa interaction δ and find that this parameter has strong influence on range of Yukawa interaction Λ. For that purpose we use parameterized post-Newtonian (PPN) equations of motion in order to calculate the simulated orbits of S-stars in GR and Yukawa gravity. Using MCMC simulations we obtain the best-fit values and uncertainties of Yukawa gravity parameters for S-stars. Also, we introduce a new criterion which can be used for classification of gravitational systems in this type of gravity, according to their scales. We demonstrated that performed analysis of the observed S-stars orbits around the GC in the frame of the Yukawa gravity represent a tool for constraining the Yukawa gravity parameters and probing the predictions of gravity theories.",
journal = "Journal of Cosmology and Astroparticle Physics",
title = "Constraints on Yukawa gravity parameters from observations of bright stars",
number = "03",
pages = "056",
doi = "10.1088/1475-7516/2023/03/056"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Zakharov, A. F.. (2023). Constraints on Yukawa gravity parameters from observations of bright stars. in Journal of Cosmology and Astroparticle Physics(03), 056.
https://doi.org/10.1088/1475-7516/2023/03/056

Jovanović P, Borka Jovanović V, Borka D, Zakharov AF. Constraints on Yukawa gravity parameters from observations of bright stars. in Journal of Cosmology and Astroparticle Physics. 2023;(03):056.
doi:10.1088/1475-7516/2023/03/056 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Zakharov, Alexander F., "Constraints on Yukawa gravity parameters from observations of bright stars" in Journal of Cosmology and Astroparticle Physics, no. 03 (2023):056,
https://doi.org/10.1088/1475-7516/2023/03/056 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
PY  - 2023
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/11358
AB  - In this study we used the observed perihelion precession of planetary orbits in the Solar System in order to constrain theory of Yukawa-type gravity, and to bound mass of graviton. For that purpose we assumed that the precession angles of the planets in Yukawa-type gravity should be equal to their observed values, as well as to the corresponding predictions of General Relativity (GR). Starting from these requests we constrain Yukawa-like gravitational potential. The obtained results showed that our estimates for the range of Yukawa interaction Λ at the Solar System scales are in good agreement with recent experimental constrains. Assuming that the estimated value of the range of Λ corresponds to the Compton wavelength of graviton λg, we then estimate the upper bound for its mass mg. We found that these estimates were in agreement with our previous results obtained from the observed stellar orbits around the Galactic Center (GC). © 2023, University of Nis. All rights reserved.
T2  - Filomat
T1  - Bounds on graviton mass and constraining Yukawa-like gravitational potential from planetary motion in the Solar System
VL  - 37
IS  - 25
SP  - 8591
EP  - 8601
UR  - https://hdl.handle.net/21.15107/rcub_vinar_11358
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Jovanović, Predrag",
year = "2023",
abstract = "In this study we used the observed perihelion precession of planetary orbits in the Solar System in order to constrain theory of Yukawa-type gravity, and to bound mass of graviton. For that purpose we assumed that the precession angles of the planets in Yukawa-type gravity should be equal to their observed values, as well as to the corresponding predictions of General Relativity (GR). Starting from these requests we constrain Yukawa-like gravitational potential. The obtained results showed that our estimates for the range of Yukawa interaction Λ at the Solar System scales are in good agreement with recent experimental constrains. Assuming that the estimated value of the range of Λ corresponds to the Compton wavelength of graviton λg, we then estimate the upper bound for its mass mg. We found that these estimates were in agreement with our previous results obtained from the observed stellar orbits around the Galactic Center (GC). © 2023, University of Nis. All rights reserved.",
journal = "Filomat",
title = "Bounds on graviton mass and constraining Yukawa-like gravitational potential from planetary motion in the Solar System",
volume = "37",
number = "25",
pages = "8591-8601",
url = "https://hdl.handle.net/21.15107/rcub_vinar_11358"
}

Borka, D., Borka Jovanović, V.,& Jovanović, P.. (2023). Bounds on graviton mass and constraining Yukawa-like gravitational potential from planetary motion in the Solar System. in Filomat, 37(25), 8591-8601.
https://hdl.handle.net/21.15107/rcub_vinar_11358

Borka D, Borka Jovanović V, Jovanović P. Bounds on graviton mass and constraining Yukawa-like gravitational potential from planetary motion in the Solar System. in Filomat. 2023;37(25):8591-8601.
https://hdl.handle.net/21.15107/rcub_vinar_11358 .

Borka, Duško, Borka Jovanović, Vesna, Jovanović, Predrag, "Bounds on graviton mass and constraining Yukawa-like gravitational potential from planetary motion in the Solar System" in Filomat, 37, no. 25 (2023):8591-8601,
https://hdl.handle.net/21.15107/rcub_vinar_11358 .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Nikolić, Violeta N.
AU  - Lazarov, Nenad Đ.
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10151
AB  - We estimate the parameters of the Hybrid Palatini gravity model with the Schwarzschild precession of S-stars, specifically of the S2, S38 and S55 stars. We also take into account the case of bulk mass distribution near the Galactic Center. We assume that the Schwarzschild orbital precession of mentioned S-stars is the same as in General Relativity (GR) in all studied cases. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. The astronomical data analysis of S38 and S55 orbits showed that, also in these cases, the orbital precession is close to the GR prediction. Based on this observational fact, we evaluated the parameters of the Hybrid Palatini Gravity model with the Schwarzschild precession of the S2, S38 and S55 stars, and we estimated the range of parameters of the Hybrid Palatini gravity model for which the orbital precession is as in GR for all three stars. We also evaluated the parameters of the Hybrid Palatini Gravity model in the case of different values of bulk mass density distribution of extended matter. We believe that proposed method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
T2  - Universe
T1  - Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution
VL  - 8
IS  - 2
SP  - 70
DO  - 10.3390/universe8020070
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Nikolić, Violeta N. and Lazarov, Nenad Đ. and Jovanović, Predrag",
year = "2022",
abstract = "We estimate the parameters of the Hybrid Palatini gravity model with the Schwarzschild precession of S-stars, specifically of the S2, S38 and S55 stars. We also take into account the case of bulk mass distribution near the Galactic Center. We assume that the Schwarzschild orbital precession of mentioned S-stars is the same as in General Relativity (GR) in all studied cases. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. The astronomical data analysis of S38 and S55 orbits showed that, also in these cases, the orbital precession is close to the GR prediction. Based on this observational fact, we evaluated the parameters of the Hybrid Palatini Gravity model with the Schwarzschild precession of the S2, S38 and S55 stars, and we estimated the range of parameters of the Hybrid Palatini gravity model for which the orbital precession is as in GR for all three stars. We also evaluated the parameters of the Hybrid Palatini Gravity model in the case of different values of bulk mass density distribution of extended matter. We believe that proposed method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.",
journal = "Universe",
title = "Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution",
volume = "8",
number = "2",
pages = "70",
doi = "10.3390/universe8020070"
}

Borka, D., Borka Jovanović, V., Nikolić, V. N., Lazarov, N. Đ.,& Jovanović, P.. (2022). Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution. in Universe, 8(2), 70.
https://doi.org/10.3390/universe8020070

Borka D, Borka Jovanović V, Nikolić VN, Lazarov NĐ, Jovanović P. Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution. in Universe. 2022;8(2):70.
doi:10.3390/universe8020070 .

Borka, Duško, Borka Jovanović, Vesna, Nikolić, Violeta N., Lazarov, Nenad Đ., Jovanović, Predrag, "Estimating the Parameters of the Hybrid Palatini Gravity Model with the Schwarzschild Precession of S2, S38 and S55 Stars: Case of Bulk Mass Distribution" in Universe, 8, no. 2 (2022):70,
https://doi.org/10.3390/universe8020070 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Capozziello, Salvatore
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10420
AB  - We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.
T2  - Advances in Space Research
T1  - Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model
VL  - 71
IS  - 2
SP  - 1235
EP  - 1244
DO  - 10.1016/j.asr.2022.08.060
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Capozziello, Salvatore and Jovanović, Predrag",
year = "2022",
abstract = "We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.",
journal = "Advances in Space Research",
title = "Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model",
volume = "71",
number = "2",
pages = "1235-1244",
doi = "10.1016/j.asr.2022.08.060"
}

Borka, D., Borka Jovanović, V., Capozziello, S.,& Jovanović, P.. (2022). Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model. in Advances in Space Research, 71(2), 1235-1244.
https://doi.org/10.1016/j.asr.2022.08.060

Borka D, Borka Jovanović V, Capozziello S, Jovanović P. Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model. in Advances in Space Research. 2022;71(2):1235-1244.
doi:10.1016/j.asr.2022.08.060 .

Borka, Duško, Borka Jovanović, Vesna, Capozziello, Salvatore, Jovanović, Predrag, "Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model" in Advances in Space Research, 71, no. 2 (2022):1235-1244,
https://doi.org/10.1016/j.asr.2022.08.060 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Arsenić, Arsenije
AU  - Jovanović, Predrag
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10341
AB  - The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy’s Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN.
T2  - Advances in Space Research
T1  - Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format
DO  - 10.1016/j.asr.2022.05.062
ER  - 

@article{
author = "Borka Jovanović, Vesna and Borka, Duško and Arsenić, Arsenije and Jovanović, Predrag",
year = "2022",
abstract = "The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy’s Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN.",
journal = "Advances in Space Research",
title = "Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format",
doi = "10.1016/j.asr.2022.05.062"
}

Borka Jovanović, V., Borka, D., Arsenić, A.,& Jovanović, P.. (2022). Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format. in Advances in Space Research.
https://doi.org/10.1016/j.asr.2022.05.062

Borka Jovanović V, Borka D, Arsenić A, Jovanović P. Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format. in Advances in Space Research. 2022;.
doi:10.1016/j.asr.2022.05.062 .

Borka Jovanović, Vesna, Borka, Duško, Arsenić, Arsenije, Jovanović, Predrag, "Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format" in Advances in Space Research (2022),
https://doi.org/10.1016/j.asr.2022.05.062 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Capozziello, Salvatore
AU  - Zakharov, Alexander F.
AU  - Jovanović, Predrag
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9981
AB  - After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first post-Newtonian (pN) approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Extended Gravity theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some Extended Gravity models including power-law f(R), general Yukawa-like corrections, scalar–tensor gravity, and non-local gravity theories formulated in both metric and Palatini formalism. In this consideration, we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these Extended Gravity models for which the orbital precession is like in GR. Then we compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, scalar–tensor gravity and non-local gravity theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center.
T2  - Universe
T1  - Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star
VL  - 7
IS  - 11
SP  - 407
DO  - 10.3390/universe7110407
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna and Capozziello, Salvatore and Zakharov, Alexander F. and Jovanović, Predrag",
year = "2021",
abstract = "After giving a short overview of previous results on constraining of Extended Gravity by stellar orbits, we discuss the Schwarzschild orbital precession of S2 star assuming the congruence with predictions of General Relativity (GR). At the moment, the S2 star trajectory is remarkably fitted with the first post-Newtonian approximation of GR. In particular, both Keck and VLT (GRAVITY) teams declared that the gravitational redshift near its pericenter passage for the S2 star orbit corresponds to theoretical estimates found with the first post-Newtonian (pN) approximation. In 2020, the GRAVITY Collaboration detected the orbital precession of the S2 star around the supermassive black hole (SMBH) at the Galactic Center and showed that it is close to the GR prediction. Based on this observational fact, we evaluated parameters of the Extended Gravity theories with the Schwarzschild precession of the S2 star. Using the mentioned method, we estimate the orbital precession angles for some Extended Gravity models including power-law f(R), general Yukawa-like corrections, scalar–tensor gravity, and non-local gravity theories formulated in both metric and Palatini formalism. In this consideration, we assume that a gravitational field is spherically symmetric, therefore, alternative theories of gravity could be described only with a few parameters. Specifically, considering the orbital precession, we estimate the range of parameters of these Extended Gravity models for which the orbital precession is like in GR. Then we compare these results with our previous results, which were obtained by fitting the simulated orbits of S2 star to its observed astrometric positions. In case of power-law f(R), generic Yukawa-like correction, scalar–tensor gravity and non-local gravity theories, we were able to obtain a prograde orbital precession, like in GR. According to these results, the method is a useful tool to evaluate parameters of the gravitational potential at the Galactic Center.",
journal = "Universe",
title = "Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star",
volume = "7",
number = "11",
pages = "407",
doi = "10.3390/universe7110407"
}

Borka, D., Borka Jovanović, V., Capozziello, S., Zakharov, A. F.,& Jovanović, P.. (2021). Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star. in Universe, 7(11), 407.
https://doi.org/10.3390/universe7110407

Borka D, Borka Jovanović V, Capozziello S, Zakharov AF, Jovanović P. Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star. in Universe. 2021;7(11):407.
doi:10.3390/universe7110407 .

Borka, Duško, Borka Jovanović, Vesna, Capozziello, Salvatore, Zakharov, Alexander F., Jovanović, Predrag, "Estimating the Parameters of Extended Gravity Theories with the Schwarzschild Precession of S2 Star" in Universe, 7, no. 11 (2021):407,
https://doi.org/10.3390/universe7110407 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9570
AB  - Abstract: Subject of this study is a theoretical investigation of the channeling of high energy protons with the radially deformed triple-wall carbon nanotubes (TWNTs). Specifically, we chose a proton energy of 1 GeV and perfect and the radially deformed TWNTs (15, 0)@(10, 0)@(5, 0) of radial strengths η= 0.1 , 0.2 and 0.3. We presented the channeling potential within the perfect and deformed TWNTs and corresponding spatial and angular distributions of channeled protons. We treated the problem relativistically. We also analyzed the case where proton beams enter nanotube under different incidence angles. We analyzed two cases L= 1 and 5 μm. We also varied the value of incidence angle of proton beam and calculated the efficiency of nanotube channeling. This is the first time that we presented spatial and angular distributions of channeled protons with radially deformed TWNTs with angular effect of proton beam, and also, for the first time we presented their channeling efficiency. Our results show that the spatial and angular distributions depend strongly on the nanotube lengths, incident angle of the proton beam, and on the level of radial deformation of nanotube. Multi-wall nanotubes (MWNTs) are better candidates for realization of ion guiding than single-wall nanotubes (SWNTs) because it is easier to produce them straight. Also, deformation of the nanotube and the incident proton beam under some initial angle with respect to the nanotube axes represent realistic situation. That is why we believe that these results may be useful for production and guiding of nanosized ion beams by nanotubes. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T1  - Guiding of protons through radially deformed triple-wall carbon nanotubes
VL  - 75
IS  - 2
SP  - 50
DO  - 10.1140/epjd/s10053-021-00039-1
ER  - 

@article{
author = "Borka, Duško and Borka Jovanović, Vesna",
year = "2021",
abstract = "Abstract: Subject of this study is a theoretical investigation of the channeling of high energy protons with the radially deformed triple-wall carbon nanotubes (TWNTs). Specifically, we chose a proton energy of 1 GeV and perfect and the radially deformed TWNTs (15, 0)@(10, 0)@(5, 0) of radial strengths η= 0.1 , 0.2 and 0.3. We presented the channeling potential within the perfect and deformed TWNTs and corresponding spatial and angular distributions of channeled protons. We treated the problem relativistically. We also analyzed the case where proton beams enter nanotube under different incidence angles. We analyzed two cases L= 1 and 5 μm. We also varied the value of incidence angle of proton beam and calculated the efficiency of nanotube channeling. This is the first time that we presented spatial and angular distributions of channeled protons with radially deformed TWNTs with angular effect of proton beam, and also, for the first time we presented their channeling efficiency. Our results show that the spatial and angular distributions depend strongly on the nanotube lengths, incident angle of the proton beam, and on the level of radial deformation of nanotube. Multi-wall nanotubes (MWNTs) are better candidates for realization of ion guiding than single-wall nanotubes (SWNTs) because it is easier to produce them straight. Also, deformation of the nanotube and the incident proton beam under some initial angle with respect to the nanotube axes represent realistic situation. That is why we believe that these results may be useful for production and guiding of nanosized ion beams by nanotubes. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.",
journal = "European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics",
title = "Guiding of protons through radially deformed triple-wall carbon nanotubes",
volume = "75",
number = "2",
pages = "50",
doi = "10.1140/epjd/s10053-021-00039-1"
}

Borka, D.,& Borka Jovanović, V.. (2021). Guiding of protons through radially deformed triple-wall carbon nanotubes. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75(2), 50.
https://doi.org/10.1140/epjd/s10053-021-00039-1

Borka D, Borka Jovanović V. Guiding of protons through radially deformed triple-wall carbon nanotubes. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics. 2021;75(2):50.
doi:10.1140/epjd/s10053-021-00039-1 .

Borka, Duško, Borka Jovanović, Vesna, "Guiding of protons through radially deformed triple-wall carbon nanotubes" in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75, no. 2 (2021):50,
https://doi.org/10.1140/epjd/s10053-021-00039-1 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
AU  - Capozziello, Salvatore
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9802
AB  - We use the Fundamental Plane of Elliptical Galaxies to constrain the so-called Hybrid Gravity, a modified theory of gravity where General Relativity is improved by further degrees of freedom of metric-affine Palatini formalism of f(R) gravity. Because the Fundamental Plane is connected to the global properties of elliptical galaxies, it is possible to obtain observational constraints on the parameters of Hybrid Gravity in the weak field limit. We analyze also the velocity distribution of elliptical galaxies comparing our theoretical results in the case of Hybrid Gravity with astronomical data for elliptical galaxies. In this way, we are able to constrain the Hybrid Gravity parameters mϕ and ϕ. We show that the Fundamental Plane, i.e., vc/ σ relations, can be used as a standard tool to probe different theories of gravity in the weak field limit. We conclude that Hybrid Gravity is able to explain elliptical galaxies with different stellar kinematics without the dark matter hypothesis. © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T1  - Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies
VL  - 75
IS  - 5
DO  - 10.1140/epjd/s10053-021-00163-y
ER  - 

@article{
author = "Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag and Capozziello, Salvatore",
year = "2021",
abstract = "We use the Fundamental Plane of Elliptical Galaxies to constrain the so-called Hybrid Gravity, a modified theory of gravity where General Relativity is improved by further degrees of freedom of metric-affine Palatini formalism of f(R) gravity. Because the Fundamental Plane is connected to the global properties of elliptical galaxies, it is possible to obtain observational constraints on the parameters of Hybrid Gravity in the weak field limit. We analyze also the velocity distribution of elliptical galaxies comparing our theoretical results in the case of Hybrid Gravity with astronomical data for elliptical galaxies. In this way, we are able to constrain the Hybrid Gravity parameters mϕ and ϕ. We show that the Fundamental Plane, i.e., vc/ σ relations, can be used as a standard tool to probe different theories of gravity in the weak field limit. We conclude that Hybrid Gravity is able to explain elliptical galaxies with different stellar kinematics without the dark matter hypothesis. © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.",
journal = "European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics",
title = "Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies",
volume = "75",
number = "5",
doi = "10.1140/epjd/s10053-021-00163-y"
}

Borka Jovanović, V., Borka, D., Jovanović, P.,& Capozziello, S.. (2021). Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75(5).
https://doi.org/10.1140/epjd/s10053-021-00163-y

Borka Jovanović V, Borka D, Jovanović P, Capozziello S. Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics. 2021;75(5).
doi:10.1140/epjd/s10053-021-00163-y .

Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, Capozziello, Salvatore, "Possible effects of hybrid gravity on stellar kinematics in elliptical galaxies" in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75, no. 5 (2021),
https://doi.org/10.1140/epjd/s10053-021-00163-y . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Zakharov, Alexander F.
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9803
AB  - In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter, and we require that the value of orbital precession is the same like in general relativity (GR). From that request we determine gravity parameter λ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter λ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter λ of the Yukawa gravity model, and to constrain the graviton mass. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T2  - European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics
T1  - Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity
VL  - 75
IS  - 5
DO  - 10.1140/epjd/s10053-021-00154-z
ER  - 

@article{
author = "Jovanović, Predrag and Borka, Duško and Borka Jovanović, Vesna and Zakharov, Alexander F.",
year = "2021",
abstract = "In this study we investigate possible applications of observed S2 orbit around Galactic Center for constraining the Yukawa gravity at scales in the range between several tens and several thousands astronomical units (AU) to obtain graviton mass constraints. In our model we suppose that bulk distribution of matter (includes stellar cluster, interstellar gas distribution and dark matter) exists near Supermassive Black Hole (SMBH) in our Galactic Center. We obtain the values of orbital precession angle for different values of mass density of matter, and we require that the value of orbital precession is the same like in general relativity (GR). From that request we determine gravity parameter λ and the upper value for graviton mass. We found that in the cases where the density of extended mass is higher, the maximum allowed value for parameter λ is smaller and the upper limit for graviton mass is higher. It is due to the fact that the extended mass causes the retrograde orbital precession. We believe that this study is a very efficient tool to evaluate a gravitational potential at the Galactic Center, parameter λ of the Yukawa gravity model, and to constrain the graviton mass. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.",
journal = "European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics",
title = "Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity",
volume = "75",
number = "5",
doi = "10.1140/epjd/s10053-021-00154-z"
}

Jovanović, P., Borka, D., Borka Jovanović, V.,& Zakharov, A. F.. (2021). Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75(5).
https://doi.org/10.1140/epjd/s10053-021-00154-z

Jovanović P, Borka D, Borka Jovanović V, Zakharov AF. Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity. in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics. 2021;75(5).
doi:10.1140/epjd/s10053-021-00154-z .

Jovanović, Predrag, Borka, Duško, Borka Jovanović, Vesna, Zakharov, Alexander F., "Influence of bulk mass distribution on orbital precession of S2 star in Yukawa gravity" in European Physical Journal D. Atoms, Molecules, Clusters and Optical Physics, 75, no. 5 (2021),
https://doi.org/10.1140/epjd/s10053-021-00154-z . .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Popović, Luka Č.
PY  - 2020
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8827
AB  - Here we study the potential observational signatures of supermassive black hole binaries (SMBHBs) in the Fe Kα line profiles emitted from the accretion disks around their components. We simulated the Fe Kα line emission from the relativistic accretion disks using ray tracing method in Kerr metric. The obtained profiles from the SMBHBs are then compared with those in the case of the single supermassive black holes (SMBHs). We considered two models of the SMBHBs: a model when the secondary SMBH is embedded in the accretion disk around the primary, causing an empty gap in the disk, and a model with clearly separated components, where the accretion disks around both primary and secondary give a significant contribution to the composite Fe Kα line emission of a such SMBHB. The obtained results showed that both models of SMBHBs can leave imprints in the form of ripples in the cores of the emitted Fe Kα line profiles, which may look like an absorption component in the line profile. However, in the case of the composite line profiles emitted from two accretion disks, these ripples could have much higher amplitudes and strongly depend on orbital phase of the system, while for those emitted from a disk with an empty gap, the corresponding ripples mostly have lower amplitudes and do not vary significantly with orbital phase. The present day X-ray telescopes are not able to detect such signatures in the observed X-ray spectra of SMBHBs. However this will be possible with the next generation of X-ray observatories, which will also enable application of such effects as a tool for studying the properties of these objects. © 2020, Astronomical Institute, Slovak Academy of Sciences.
T2  - Contributions of the Astronomical Observatory Skalnaté Pleso
T1  - Possible observational signatures of supermassive black hole binaries in their Fe Kα line profiles
VL  - 50
IS  - 1
SP  - 219
EP  - 234
DO  - 10.31577/caosp.2020.50.1.219
ER  - 

@article{
author = "Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško and Popović, Luka Č.",
year = "2020",
abstract = "Here we study the potential observational signatures of supermassive black hole binaries (SMBHBs) in the Fe Kα line profiles emitted from the accretion disks around their components. We simulated the Fe Kα line emission from the relativistic accretion disks using ray tracing method in Kerr metric. The obtained profiles from the SMBHBs are then compared with those in the case of the single supermassive black holes (SMBHs). We considered two models of the SMBHBs: a model when the secondary SMBH is embedded in the accretion disk around the primary, causing an empty gap in the disk, and a model with clearly separated components, where the accretion disks around both primary and secondary give a significant contribution to the composite Fe Kα line emission of a such SMBHB. The obtained results showed that both models of SMBHBs can leave imprints in the form of ripples in the cores of the emitted Fe Kα line profiles, which may look like an absorption component in the line profile. However, in the case of the composite line profiles emitted from two accretion disks, these ripples could have much higher amplitudes and strongly depend on orbital phase of the system, while for those emitted from a disk with an empty gap, the corresponding ripples mostly have lower amplitudes and do not vary significantly with orbital phase. The present day X-ray telescopes are not able to detect such signatures in the observed X-ray spectra of SMBHBs. However this will be possible with the next generation of X-ray observatories, which will also enable application of such effects as a tool for studying the properties of these objects. © 2020, Astronomical Institute, Slovak Academy of Sciences.",
journal = "Contributions of the Astronomical Observatory Skalnaté Pleso",
title = "Possible observational signatures of supermassive black hole binaries in their Fe Kα line profiles",
volume = "50",
number = "1",
pages = "219-234",
doi = "10.31577/caosp.2020.50.1.219"
}

Jovanović, P., Borka Jovanović, V., Borka, D.,& Popović, L. Č.. (2020). Possible observational signatures of supermassive black hole binaries in their Fe Kα line profiles. in Contributions of the Astronomical Observatory Skalnaté Pleso, 50(1), 219-234.
https://doi.org/10.31577/caosp.2020.50.1.219

Jovanović P, Borka Jovanović V, Borka D, Popović LČ. Possible observational signatures of supermassive black hole binaries in their Fe Kα line profiles. in Contributions of the Astronomical Observatory Skalnaté Pleso. 2020;50(1):219-234.
doi:10.31577/caosp.2020.50.1.219 .

Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, Popović, Luka Č., "Possible observational signatures of supermassive black hole binaries in their Fe Kα line profiles" in Contributions of the Astronomical Observatory Skalnaté Pleso, 50, no. 1 (2020):219-234,
https://doi.org/10.31577/caosp.2020.50.1.219 . .

TY  - JOUR
AU  - Zakharov, Alexander F.
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
PY  - 2020
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8826
AB  - It is established that there are supermassive black holes in centers of galaxies. A supermassive black hole with mass around 4 × 106 M⊙ is located at the Galactic Center. Such an approach for the Galactic Center looks rather natural, in spite of that consequences of model must be checked with observa- tions. We discuss opportunities to check this with forthcoming observations of shadows in mm band for the Galactic Center as it was done recently for M87*. Observations of bright stars moving near the Galactic Center gives another op-portunity to evaluate gravitational potential. We discuss opportunities to use these observations to constrain alternative theories of gravity. © 2020, Astronomical Institute, Slovak Academy of Sciences.
T2  - Contributions of the Astronomical Observatory Skalnaté Pleso
T1  - Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities
VL  - 50
IS  - 1
SP  - 203
EP  - 218
DO  - 10.31577/caosp.2020.50.1.203
ER  - 

@article{
author = "Zakharov, Alexander F. and Jovanović, Predrag and Borka, Duško and Borka Jovanović, Vesna",
year = "2020",
abstract = "It is established that there are supermassive black holes in centers of galaxies. A supermassive black hole with mass around 4 × 106 M⊙ is located at the Galactic Center. Such an approach for the Galactic Center looks rather natural, in spite of that consequences of model must be checked with observa- tions. We discuss opportunities to check this with forthcoming observations of shadows in mm band for the Galactic Center as it was done recently for M87*. Observations of bright stars moving near the Galactic Center gives another op-portunity to evaluate gravitational potential. We discuss opportunities to use these observations to constrain alternative theories of gravity. © 2020, Astronomical Institute, Slovak Academy of Sciences.",
journal = "Contributions of the Astronomical Observatory Skalnaté Pleso",
title = "Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities",
volume = "50",
number = "1",
pages = "203-218",
doi = "10.31577/caosp.2020.50.1.203"
}

Zakharov, A. F., Jovanović, P., Borka, D.,& Borka Jovanović, V.. (2020). Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities. in Contributions of the Astronomical Observatory Skalnaté Pleso, 50(1), 203-218.
https://doi.org/10.31577/caosp.2020.50.1.203

Zakharov AF, Jovanović P, Borka D, Borka Jovanović V. Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities. in Contributions of the Astronomical Observatory Skalnaté Pleso. 2020;50(1):203-218.
doi:10.31577/caosp.2020.50.1.203 .

Zakharov, Alexander F., Jovanović, Predrag, Borka, Duško, Borka Jovanović, Vesna, "Observational tests of general relativity and alternative theories of gravity with Galactic Center observations using current and future large observational facilities" in Contributions of the Astronomical Observatory Skalnaté Pleso, 50, no. 1 (2020):203-218,
https://doi.org/10.31577/caosp.2020.50.1.203 . .

TY  - JOUR
AU  - Capozziello, Salvatore
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2020
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8951
AB  - We show that fundamental plane of elliptical galaxies can be used to obtain observational constraints on metric theories of gravity. Being it connected to global properties of ellipticals, it can fix parameters of modified gravity. Specifically, we use fundamental plane to constrain modified theories of gravity with Yukawa-like corrections which commonly emerge in the post-Newtonian limit. After giving examples on how these corrections are derived, we first analyze the velocity distribution of elliptical galaxies comparing theoretical results of modified gravity with Yukawa-like corrections with astronomical data. According to these results, it is possible to constrain the parameters of the corrections discriminating among classes of models compatible with astronomical observations. We conclude that fundamental plane can be used as a standard tool to probe different theories of gravity in the weak field limit.
T2  - Physics of the Dark Universe
T1  - Constraining theories of gravity by fundamental plane of elliptical galaxies
VL  - 29
SP  - 100573
DO  - 10.1016/j.dark.2020.100573
ER  - 

@article{
author = "Capozziello, Salvatore and Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2020",
abstract = "We show that fundamental plane of elliptical galaxies can be used to obtain observational constraints on metric theories of gravity. Being it connected to global properties of ellipticals, it can fix parameters of modified gravity. Specifically, we use fundamental plane to constrain modified theories of gravity with Yukawa-like corrections which commonly emerge in the post-Newtonian limit. After giving examples on how these corrections are derived, we first analyze the velocity distribution of elliptical galaxies comparing theoretical results of modified gravity with Yukawa-like corrections with astronomical data. According to these results, it is possible to constrain the parameters of the corrections discriminating among classes of models compatible with astronomical observations. We conclude that fundamental plane can be used as a standard tool to probe different theories of gravity in the weak field limit.",
journal = "Physics of the Dark Universe",
title = "Constraining theories of gravity by fundamental plane of elliptical galaxies",
volume = "29",
pages = "100573",
doi = "10.1016/j.dark.2020.100573"
}

Capozziello, S., Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2020). Constraining theories of gravity by fundamental plane of elliptical galaxies. in Physics of the Dark Universe, 29, 100573.
https://doi.org/10.1016/j.dark.2020.100573

Capozziello S, Borka Jovanović V, Borka D, Jovanović P. Constraining theories of gravity by fundamental plane of elliptical galaxies. in Physics of the Dark Universe. 2020;29:100573.
doi:10.1016/j.dark.2020.100573 .

Capozziello, Salvatore, Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Constraining theories of gravity by fundamental plane of elliptical galaxies" in Physics of the Dark Universe, 29 (2020):100573,
https://doi.org/10.1016/j.dark.2020.100573 . .

TY  - JOUR
AU  - Dialektopoulos, Konstantinos F.
AU  - Borka, Duško
AU  - Capozziello, Salvatore
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
PY  - 2019
UR  - https://link.aps.org/doi/10.1103/PhysRevD.99.044053
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8084
AB  - Nonlocal theories of gravity have recently drawn a lot of attention because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether symmetries, it can be shown that the only nontrivial form of the distortion function is the exponential one, which is working not only for cosmological minisuperspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak-field approximation of this type of nonlocal gravity, and comparing with the orbits of the S2 star around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Nonlocal effects do not play a significant role on the orbits of S2 stars around Sgr A∗ but give richer phenomenology at cosmological scales than the ΛCDM model. Also, we show that the nonlocal gravity model gives better agreement between theory and astronomical observations than Keplerian orbits. © 2019 American Physical Society.
T2  - Physical Review D
T1  - Constraining nonlocal gravity by S2 star orbits
VL  - 99
IS  - 4
SP  - 044053
DO  - 10.1103/PhysRevD.99.044053
ER  - 

@article{
author = "Dialektopoulos, Konstantinos F. and Borka, Duško and Capozziello, Salvatore and Borka Jovanović, Vesna and Jovanović, Predrag",
year = "2019",
abstract = "Nonlocal theories of gravity have recently drawn a lot of attention because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether symmetries, it can be shown that the only nontrivial form of the distortion function is the exponential one, which is working not only for cosmological minisuperspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak-field approximation of this type of nonlocal gravity, and comparing with the orbits of the S2 star around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Nonlocal effects do not play a significant role on the orbits of S2 stars around Sgr A∗ but give richer phenomenology at cosmological scales than the ΛCDM model. Also, we show that the nonlocal gravity model gives better agreement between theory and astronomical observations than Keplerian orbits. © 2019 American Physical Society.",
journal = "Physical Review D",
title = "Constraining nonlocal gravity by S2 star orbits",
volume = "99",
number = "4",
pages = "044053",
doi = "10.1103/PhysRevD.99.044053"
}

Dialektopoulos, K. F., Borka, D., Capozziello, S., Borka Jovanović, V.,& Jovanović, P.. (2019). Constraining nonlocal gravity by S2 star orbits. in Physical Review D, 99(4), 044053.
https://doi.org/10.1103/PhysRevD.99.044053

Dialektopoulos KF, Borka D, Capozziello S, Borka Jovanović V, Jovanović P. Constraining nonlocal gravity by S2 star orbits. in Physical Review D. 2019;99(4):044053.
doi:10.1103/PhysRevD.99.044053 .

Dialektopoulos, Konstantinos F., Borka, Duško, Capozziello, Salvatore, Borka Jovanović, Vesna, Jovanović, Predrag, "Constraining nonlocal gravity by S2 star orbits" in Physical Review D, 99, no. 4 (2019):044053,
https://doi.org/10.1103/PhysRevD.99.044053 . .

TY  - JOUR
AU  - Dialektopoulos, Konstantinos F.
AU  - Borka, Duško
AU  - Capozziello, Salvatore
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
PY  - 2019
UR  - https://link.aps.org/doi/10.1103/PhysRevD.99.044053
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8090
AB  - Nonlocal theories of gravity have recently drawn a lot of attention because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether symmetries, it can be shown that the only nontrivial form of the distortion function is the exponential one, which is working not only for cosmological minisuperspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak-field approximation of this type of nonlocal gravity, and comparing with the orbits of the S2 star around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Nonlocal effects do not play a significant role on the orbits of S2 stars around Sgr A∗ but give richer phenomenology at cosmological scales than the ΛCDM model. Also, we show that the nonlocal gravity model gives better agreement between theory and astronomical observations than Keplerian orbits.
T2  - Physical Review D
T1  - Constraining nonlocal gravity by S2 star orbits
VL  - 99
IS  - 4
SP  - 044053
DO  - 10.1103/PhysRevD.99.044053
ER  - 

@article{
author = "Dialektopoulos, Konstantinos F. and Borka, Duško and Capozziello, Salvatore and Borka Jovanović, Vesna and Jovanović, Predrag",
year = "2019",
abstract = "Nonlocal theories of gravity have recently drawn a lot of attention because they can suitably represent the behavior of gravitational interaction in the ultraviolet regime. Furthermore, at infrared scales, they give rise to notable cosmological effects which could be important to describe the dark energy behavior. In particular, exponential forms of the distortion function seem particularly useful for this purpose. Using Noether symmetries, it can be shown that the only nontrivial form of the distortion function is the exponential one, which is working not only for cosmological minisuperspaces, but also in a spherically symmetric spacetime. Taking this result into account, we study the weak-field approximation of this type of nonlocal gravity, and comparing with the orbits of the S2 star around the Galactic center (NTT/VLT data), we set constraints on the parameters of the theory. Nonlocal effects do not play a significant role on the orbits of S2 stars around Sgr A∗ but give richer phenomenology at cosmological scales than the ΛCDM model. Also, we show that the nonlocal gravity model gives better agreement between theory and astronomical observations than Keplerian orbits.",
journal = "Physical Review D",
title = "Constraining nonlocal gravity by S2 star orbits",
volume = "99",
number = "4",
pages = "044053",
doi = "10.1103/PhysRevD.99.044053"
}

Dialektopoulos, K. F., Borka, D., Capozziello, S., Borka Jovanović, V.,& Jovanović, P.. (2019). Constraining nonlocal gravity by S2 star orbits. in Physical Review D, 99(4), 044053.
https://doi.org/10.1103/PhysRevD.99.044053

Dialektopoulos KF, Borka D, Capozziello S, Borka Jovanović V, Jovanović P. Constraining nonlocal gravity by S2 star orbits. in Physical Review D. 2019;99(4):044053.
doi:10.1103/PhysRevD.99.044053 .

Dialektopoulos, Konstantinos F., Borka, Duško, Capozziello, Salvatore, Borka Jovanović, Vesna, Jovanović, Predrag, "Constraining nonlocal gravity by S2 star orbits" in Physical Review D, 99, no. 4 (2019):044053,
https://doi.org/10.1103/PhysRevD.99.044053 . .

TY  - CONF
AU  - Ignjatović, Siniša R.
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
AU  - Jovanović, Predrag
PY  - 2019
UR  - http://aip.scitation.org/doi/abs/10.1063/1.5091205
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8093
AB  - The simplest form of the Hyperfine Interaction (HFI) of quarks is a color-spin interaction, sometimes called Fermi-Breit (FB) HFI. For conventional hadrons, this HFI for quark-antiquark (qq) pairs is twice as strong as the same HFI for quark-quark (qq or qq) pairs, but this difference is absorbed into the different HFI constants for mesons and baryons, which are free parameters of the fits. For tetraquarks, however, qqHFI is only half as strong as the qq/qqHFI and both kinds of pairs coexist within the same state. Hence it is worth investigating a model with different fit constants for qq and qq/q pairs. We have investigated 3 models of spin-color HFI for light scalar tetraquarks: 2 models with single constants for both kinds of pairs and one model with different fit constants. The light scalar nonet is chosen because of a lack of other experimentally observed multiplets interpretable as pure exotic states. Since even the nonet contains only 3 particles with distinct masses (i. e. 3 fit points), the constituent quark masses had to be taken from conventional hadron fits obtained in our previous work. The two-constant model did not prove to be a viable alternative to the one-constant models. © 2019 Author(s).
C3  - AIP Conference Proceedings
T1  - Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states
VL  - 2075
SP  - 080004
DO  - 10.1063/1.5091205
ER  - 

@conference{
author = "Ignjatović, Siniša R. and Borka Jovanović, Vesna and Borka, Duško and Jovanović, Predrag",
year = "2019",
abstract = "The simplest form of the Hyperfine Interaction (HFI) of quarks is a color-spin interaction, sometimes called Fermi-Breit (FB) HFI. For conventional hadrons, this HFI for quark-antiquark (qq) pairs is twice as strong as the same HFI for quark-quark (qq or qq) pairs, but this difference is absorbed into the different HFI constants for mesons and baryons, which are free parameters of the fits. For tetraquarks, however, qqHFI is only half as strong as the qq/qqHFI and both kinds of pairs coexist within the same state. Hence it is worth investigating a model with different fit constants for qq and qq/q pairs. We have investigated 3 models of spin-color HFI for light scalar tetraquarks: 2 models with single constants for both kinds of pairs and one model with different fit constants. The light scalar nonet is chosen because of a lack of other experimentally observed multiplets interpretable as pure exotic states. Since even the nonet contains only 3 particles with distinct masses (i. e. 3 fit points), the constituent quark masses had to be taken from conventional hadron fits obtained in our previous work. The two-constant model did not prove to be a viable alternative to the one-constant models. © 2019 Author(s).",
journal = "AIP Conference Proceedings",
title = "Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states",
volume = "2075",
pages = "080004",
doi = "10.1063/1.5091205"
}

Ignjatović, S. R., Borka Jovanović, V., Borka, D.,& Jovanović, P.. (2019). Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states. in AIP Conference Proceedings, 2075, 080004.
https://doi.org/10.1063/1.5091205

Ignjatović SR, Borka Jovanović V, Borka D, Jovanović P. Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states. in AIP Conference Proceedings. 2019;2075:080004.
doi:10.1063/1.5091205 .

Ignjatović, Siniša R., Borka Jovanović, Vesna, Borka, Duško, Jovanović, Predrag, "Hyperfine interactions of constituent quarks and the mass spectrum of tetraquark states" in AIP Conference Proceedings, 2075 (2019):080004,
https://doi.org/10.1063/1.5091205 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Galijaš, Sava M. D.
PY  - 2019
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8502
AB  - This study is devoted to the angular and spatial distribution of protons channeling through a bent and radially deformed single-wall boron-nitride nanotubes (SWBNNTs). These nanotubes are more thermal and chemical stable then carbon nanotubes, and they are good candidates for future channeling experiments. This investigation is continuation of our previous study [1, 2] and now we investigate channeling properties of SWBNNTs as a function of the very realistic effects: bending angle of nanotube and its radial deformation. For the first time we presented here investigation of these effects with boron-nitride nanotubes and combination of both effect. The angular and spatial distributions of channeled protons were generated using the Molière’s expression for the continuum potential of the SWBNNT’s atoms and computer simulation method. We also calculate the total yield of protons channeled in the nanotubes as a function of the bending angle. We demonstrate that varying bending angle and taking into account radial deformation we can get a significant rearrangement of the propagating protons within the boron-nitride nanotube. This investigation may be very useful to give us detailed information on the relevant interaction potentials inside SWBNNTs and for creating nanosized proton beams to be used in different applications in medicine and materials science. © 2019, Editura Academiei Romane. All rights reserved.
T2  - Romanian Reports in Physics
T1  - Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes
VL  - 71
IS  - 3
SP  - 207
UR  - https://hdl.handle.net/21.15107/rcub_vinar_8502
ER  - 

@article{
author = "Borka, Duško and Galijaš, Sava M. D.",
year = "2019",
abstract = "This study is devoted to the angular and spatial distribution of protons channeling through a bent and radially deformed single-wall boron-nitride nanotubes (SWBNNTs). These nanotubes are more thermal and chemical stable then carbon nanotubes, and they are good candidates for future channeling experiments. This investigation is continuation of our previous study [1, 2] and now we investigate channeling properties of SWBNNTs as a function of the very realistic effects: bending angle of nanotube and its radial deformation. For the first time we presented here investigation of these effects with boron-nitride nanotubes and combination of both effect. The angular and spatial distributions of channeled protons were generated using the Molière’s expression for the continuum potential of the SWBNNT’s atoms and computer simulation method. We also calculate the total yield of protons channeled in the nanotubes as a function of the bending angle. We demonstrate that varying bending angle and taking into account radial deformation we can get a significant rearrangement of the propagating protons within the boron-nitride nanotube. This investigation may be very useful to give us detailed information on the relevant interaction potentials inside SWBNNTs and for creating nanosized proton beams to be used in different applications in medicine and materials science. © 2019, Editura Academiei Romane. All rights reserved.",
journal = "Romanian Reports in Physics",
title = "Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes",
volume = "71",
number = "3",
pages = "207",
url = "https://hdl.handle.net/21.15107/rcub_vinar_8502"
}

Borka, D.,& Galijaš, S. M. D.. (2019). Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes. in Romanian Reports in Physics, 71(3), 207.
https://hdl.handle.net/21.15107/rcub_vinar_8502

Borka D, Galijaš SMD. Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes. in Romanian Reports in Physics. 2019;71(3):207.
https://hdl.handle.net/21.15107/rcub_vinar_8502 .

Borka, Duško, Galijaš, Sava M. D., "Angular and spatial distributions of protons channeled in a bent and radially deformed single-wall boron-nitride nanotubes" in Romanian Reports in Physics, 71, no. 3 (2019):207,
https://hdl.handle.net/21.15107/rcub_vinar_8502 .

TY  - JOUR
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
PY  - 2019
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8788
AB  - In this work we used the observed additional perihelion precession in the Solar System, obtained from the observations of planets and spacecrafts, to study the possible existence of Yukawa correction term to the Newtonian gravitational potential. Our study was motivated by previous analyses which indicated the possible discrepancies from Newtonian gravity in this form and at wide range of astrophysical scales. Yukawa gravity was introduced to cure some shortcomings of General Relativity (GR) at galactic and extragalactic scales. We demonstrated that this form of gravity can give the values for orbital precession which are comparable or even in better agreement with observations than the corresponding predictions of GR. The obtained results can be used for setting stronger constraints on variation of the gravitational constant G, as well as on the fundamental constant δ of Yukawa gravity. Moreover, Yukawa gravity could be used to improve the results for the motion of planets, other Solar System bodies, as well as spacecrafts, and as a consequence, it can help us to get more reliable predictions for natural hazards in the Solar System, such as potential impacts by near-Earth objects. © 2019, Geographical Institute "Jovan Cviji" of the Serbian Academy of Sciences and Arts. All rights reserved.
T2  - Journal of the Geographical Institute Jovan Cvijic, SASA
T1  - Constraining Yukawa gravity from planetary motion in the solar system
VL  - 69
IS  - 3
SP  - 265
EP  - 269
DO  - 10.2298/IJGI1903265J
ER  - 

@article{
author = "Jovanović, Predrag and Borka, Duško and Borka Jovanović, Vesna",
year = "2019",
abstract = "In this work we used the observed additional perihelion precession in the Solar System, obtained from the observations of planets and spacecrafts, to study the possible existence of Yukawa correction term to the Newtonian gravitational potential. Our study was motivated by previous analyses which indicated the possible discrepancies from Newtonian gravity in this form and at wide range of astrophysical scales. Yukawa gravity was introduced to cure some shortcomings of General Relativity (GR) at galactic and extragalactic scales. We demonstrated that this form of gravity can give the values for orbital precession which are comparable or even in better agreement with observations than the corresponding predictions of GR. The obtained results can be used for setting stronger constraints on variation of the gravitational constant G, as well as on the fundamental constant δ of Yukawa gravity. Moreover, Yukawa gravity could be used to improve the results for the motion of planets, other Solar System bodies, as well as spacecrafts, and as a consequence, it can help us to get more reliable predictions for natural hazards in the Solar System, such as potential impacts by near-Earth objects. © 2019, Geographical Institute "Jovan Cviji" of the Serbian Academy of Sciences and Arts. All rights reserved.",
journal = "Journal of the Geographical Institute Jovan Cvijic, SASA",
title = "Constraining Yukawa gravity from planetary motion in the solar system",
volume = "69",
number = "3",
pages = "265-269",
doi = "10.2298/IJGI1903265J"
}

Jovanović, P., Borka, D.,& Borka Jovanović, V.. (2019). Constraining Yukawa gravity from planetary motion in the solar system. in Journal of the Geographical Institute Jovan Cvijic, SASA, 69(3), 265-269.
https://doi.org/10.2298/IJGI1903265J

Jovanović P, Borka D, Borka Jovanović V. Constraining Yukawa gravity from planetary motion in the solar system. in Journal of the Geographical Institute Jovan Cvijic, SASA. 2019;69(3):265-269.
doi:10.2298/IJGI1903265J .

Jovanović, Predrag, Borka, Duško, Borka Jovanović, Vesna, "Constraining Yukawa gravity from planetary motion in the solar system" in Journal of the Geographical Institute Jovan Cvijic, SASA, 69, no. 3 (2019):265-269,
https://doi.org/10.2298/IJGI1903265J . .

TY  - CONF
AU  - Politano, A.
AU  - Radović, Ivan
AU  - Borka, Duško
AU  - Mišković, Zoran L.
AU  - Chiarello, G.
PY  - 2018
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/12675
AB  - We present a theoretical modeling of the electron energy loss spectroscopy data for monolayer graphene supported by Pt(111), Ru(0001), and Ni(111) substrates. In order to reproduce the experimental loss function, we have used a two-dimensional, two-fluid hydrodynamic model for inter-band transitions of graphene’s π and σ electrons and an empirical Drude-Lorentz model in the local approximation for metal substrates. The agreement between the theoretical curves and the experimental data is very good in the cases of graphene supported by Pt and Ru substrates. Conversely, the agreement is less satisfactory for the case of graphene/Ni, presumably due to the strong hybridization between the π states of graphene and the d bands of Ni, which is not accounted for in the model.
PB  - Vilnius, Lithuania : Vilnius University, Physics Faculty
C3  - COST Action CA15107 meeting : “Multi-functional Nano-Carbon Composite Materials Network“ : Programme and abstracts
T1  - Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates
SP  - 31
EP  - 31
UR  - https://hdl.handle.net/21.15107/rcub_vinar_12675
ER  - 

@conference{
author = "Politano, A. and Radović, Ivan and Borka, Duško and Mišković, Zoran L. and Chiarello, G.",
year = "2018",
abstract = "We present a theoretical modeling of the electron energy loss spectroscopy data for monolayer graphene supported by Pt(111), Ru(0001), and Ni(111) substrates. In order to reproduce the experimental loss function, we have used a two-dimensional, two-fluid hydrodynamic model for inter-band transitions of graphene’s π and σ electrons and an empirical Drude-Lorentz model in the local approximation for metal substrates. The agreement between the theoretical curves and the experimental data is very good in the cases of graphene supported by Pt and Ru substrates. Conversely, the agreement is less satisfactory for the case of graphene/Ni, presumably due to the strong hybridization between the π states of graphene and the d bands of Ni, which is not accounted for in the model.",
publisher = "Vilnius, Lithuania : Vilnius University, Physics Faculty",
journal = "COST Action CA15107 meeting : “Multi-functional Nano-Carbon Composite Materials Network“ : Programme and abstracts",
title = "Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates",
pages = "31-31",
url = "https://hdl.handle.net/21.15107/rcub_vinar_12675"
}

Politano, A., Radović, I., Borka, D., Mišković, Z. L.,& Chiarello, G.. (2018). Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates. in COST Action CA15107 meeting : “Multi-functional Nano-Carbon Composite Materials Network“ : Programme and abstracts
Vilnius, Lithuania : Vilnius University, Physics Faculty., 31-31.
https://hdl.handle.net/21.15107/rcub_vinar_12675

Politano A, Radović I, Borka D, Mišković ZL, Chiarello G. Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates. in COST Action CA15107 meeting : “Multi-functional Nano-Carbon Composite Materials Network“ : Programme and abstracts. 2018;:31-31.
https://hdl.handle.net/21.15107/rcub_vinar_12675 .

Politano, A., Radović, Ivan, Borka, Duško, Mišković, Zoran L., Chiarello, G., "Theoretical modeling of experimental EELS data for monolayer graphene supported by different metal substrates" in COST Action CA15107 meeting : “Multi-functional Nano-Carbon Composite Materials Network“ : Programme and abstracts (2018):31-31,
https://hdl.handle.net/21.15107/rcub_vinar_12675 .

TY  - JOUR
AU  - Maljković, Jelena B.
AU  - Borka, Duško
AU  - Ranković, Miloš Lj.
AU  - Marinković, Bratislav P.
AU  - Milosavljević, Aleksandar R.
AU  - Lemell, Christoph
AU  - Tokesi, Karoly
PY  - 2018
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/7656
AB  - The transmission of low-energy electrons through a macroscopic steel capillary has been investigated both experimentally and theoretically. The length of the steel capillary was L = 19.5 mm and the inner diameter was d = 0.9 mm. The kinetic energy distribution of electrons transmitted through the steel capillary was recorded for a tilt angle of psi = 2.6 degrees of the incident electron beam with respect to the capillary axis. Accompanying simulations based on classical transport theory reproduce the experimental data to a high degree of agreement. Transmission for other tilt angles has also been simulated to investigate the influence of the tilt angle on the guiding efficiency.
T2  - Nuclear Instruments and Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms
T1  - Electron transmission through a steel capillary
VL  - 423
SP  - 87
EP  - 91
DO  - 10.1016/j.nimb.2018.03.020
ER  - 

@article{
author = "Maljković, Jelena B. and Borka, Duško and Ranković, Miloš Lj. and Marinković, Bratislav P. and Milosavljević, Aleksandar R. and Lemell, Christoph and Tokesi, Karoly",
year = "2018",
abstract = "The transmission of low-energy electrons through a macroscopic steel capillary has been investigated both experimentally and theoretically. The length of the steel capillary was L = 19.5 mm and the inner diameter was d = 0.9 mm. The kinetic energy distribution of electrons transmitted through the steel capillary was recorded for a tilt angle of psi = 2.6 degrees of the incident electron beam with respect to the capillary axis. Accompanying simulations based on classical transport theory reproduce the experimental data to a high degree of agreement. Transmission for other tilt angles has also been simulated to investigate the influence of the tilt angle on the guiding efficiency.",
journal = "Nuclear Instruments and Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms",
title = "Electron transmission through a steel capillary",
volume = "423",
pages = "87-91",
doi = "10.1016/j.nimb.2018.03.020"
}

Maljković, J. B., Borka, D., Ranković, M. Lj., Marinković, B. P., Milosavljević, A. R., Lemell, C.,& Tokesi, K.. (2018). Electron transmission through a steel capillary. in Nuclear Instruments and Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms, 423, 87-91.
https://doi.org/10.1016/j.nimb.2018.03.020

Maljković JB, Borka D, Ranković ML, Marinković BP, Milosavljević AR, Lemell C, Tokesi K. Electron transmission through a steel capillary. in Nuclear Instruments and Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms. 2018;423:87-91.
doi:10.1016/j.nimb.2018.03.020 .

Maljković, Jelena B., Borka, Duško, Ranković, Miloš Lj., Marinković, Bratislav P., Milosavljević, Aleksandar R., Lemell, Christoph, Tokesi, Karoly, "Electron transmission through a steel capillary" in Nuclear Instruments and Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms, 423 (2018):87-91,
https://doi.org/10.1016/j.nimb.2018.03.020 . .

TY  - JOUR
AU  - Zakharov, Alexander F.
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
PY  - 2018
UR  - http://stacks.iop.org/1475-7516/2018/i=04/a=050?key=crossref.a23e3c8d44b40fe0c07114ff29f9d9ae
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/7668
AB  - Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as m(g) < 1.2 x 10(-22) eV {[}1] (see also more details in a complimentary paper {[}2]). In our previous papers we considered constraints on Yukawa gravity parameters {[}3] and on graviton mass from analysis of the trajectory of S2 star near the Galactic Center {[}4]. In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity {[}3] and graviton mass {[}4] from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around 5 x 10(-23) eV or slightly better than current estimates obtained with LIGO observations.
T2  - Journal of Cosmology and Astroparticle Physics
T1  - Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds
VL  - 2018
IS  - 04
SP  - 050
EP  - 050
DO  - 10.1088/1475-7516/2018/04/050
ER  - 

@article{
author = "Zakharov, Alexander F. and Jovanović, Predrag and Borka, Duško and Borka Jovanović, Vesna",
year = "2018",
abstract = "Recently, the LIGO-Virgo collaboration discovered gravitational waves and in their first publication on the subject the authors also presented a graviton mass constraint as m(g) < 1.2 x 10(-22) eV {[}1] (see also more details in a complimentary paper {[}2]). In our previous papers we considered constraints on Yukawa gravity parameters {[}3] and on graviton mass from analysis of the trajectory of S2 star near the Galactic Center {[}4]. In the paper we analyze a potential to reduce upper bounds for graviton mass with future observational data on trajectories of bright stars near the Galactic Center. Since gravitational potentials are different for these two cases, expressions for relativistic advance for general relativity and Yukawa potential are different functions on eccentricity and semimajor axis, it gives an opportunity to improve current estimates of graviton mass with future observational facilities. In our considerations of an improvement potential for a graviton mass estimate we adopt a conservative strategy and assume that trajectories of bright stars and their apocenter advance will be described with general relativity expressions and it gives opportunities to improve graviton mass constraints. In contrast with our previous studies, where we present current constraints on parameters of Yukawa gravity {[}3] and graviton mass {[}4] from observations of S2 star, in the paper we express expectations to improve current constraints for graviton mass, assuming the GR predictions about apocenter shifts will be confirmed with future observations. We concluded that if future observations of bright star orbits during around fifty years will confirm GR predictions about apocenter shifts of bright star orbits it give an opportunity to constrain a graviton mass at a level around 5 x 10(-23) eV or slightly better than current estimates obtained with LIGO observations.",
journal = "Journal of Cosmology and Astroparticle Physics",
title = "Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds",
volume = "2018",
number = "04",
pages = "050-050",
doi = "10.1088/1475-7516/2018/04/050"
}

Zakharov, A. F., Jovanović, P., Borka, D.,& Borka Jovanović, V.. (2018). Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds. in Journal of Cosmology and Astroparticle Physics, 2018(04), 050-050.
https://doi.org/10.1088/1475-7516/2018/04/050

Zakharov AF, Jovanović P, Borka D, Borka Jovanović V. Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds. in Journal of Cosmology and Astroparticle Physics. 2018;2018(04):050-050.
doi:10.1088/1475-7516/2018/04/050 .

Zakharov, Alexander F., Jovanović, Predrag, Borka, Duško, Borka Jovanović, Vesna, "Constraining the range of Yukawa gravity interaction from S2 star orbits III: improvement expectations for graviton mass bounds" in Journal of Cosmology and Astroparticle Physics, 2018, no. 04 (2018):050-050,
https://doi.org/10.1088/1475-7516/2018/04/050 . .

TY  - CONF
AU  - Capozziello, Salvatore
AU  - Borka, Duško
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
PY  - 2018
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/7748
AB  - We demonstrate that the existence of a Noether symmetry in f (R) theories of gravity gives rise to an additional gravitational radius, besides the standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Tully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis. Furthermore, under the same standard, the Fundamental Plane of elliptical galaxies can be addressed.
C3  - Galaxies
T1  - Galactic Structures from Gravitational Radii
VL  - 6
IS  - 1
SP  - 22
DO  - 10.3390/galaxies6010022
ER  - 

@conference{
author = "Capozziello, Salvatore and Borka, Duško and Borka Jovanović, Vesna and Jovanović, Predrag",
year = "2018",
abstract = "We demonstrate that the existence of a Noether symmetry in f (R) theories of gravity gives rise to an additional gravitational radius, besides the standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Tully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis. Furthermore, under the same standard, the Fundamental Plane of elliptical galaxies can be addressed.",
journal = "Galaxies",
title = "Galactic Structures from Gravitational Radii",
volume = "6",
number = "1",
pages = "22",
doi = "10.3390/galaxies6010022"
}

Capozziello, S., Borka, D., Borka Jovanović, V.,& Jovanović, P.. (2018). Galactic Structures from Gravitational Radii. in Galaxies, 6(1), 22.
https://doi.org/10.3390/galaxies6010022

Capozziello S, Borka D, Borka Jovanović V, Jovanović P. Galactic Structures from Gravitational Radii. in Galaxies. 2018;6(1):22.
doi:10.3390/galaxies6010022 .

Capozziello, Salvatore, Borka, Duško, Borka Jovanović, Vesna, Jovanović, Predrag, "Galactic Structures from Gravitational Radii" in Galaxies, 6, no. 1 (2018):22,
https://doi.org/10.3390/galaxies6010022 . .