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 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  - 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  - 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 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Capozziello, Salvatore
PY  - 2018
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/7781
AB  - The role of f(R) gravity, as well as the other modifications of standard Einstein’s gravity, is to explain the accelerated expansion, structure formation of the Universe, and some other phenomena at extragalactic scales (such as e.g. flat rotation curves of spiral galaxies) without adding unknown forms of dark energy or dark matter. In f(R) model, the Ricci scalar in the Einstein–Hilbert action is replaced by a general function of it. Its power-law form Rn is analyzed here using observed orbits of S-stars around the Galactic Center and also their computer simulations. We review the various consequences of the Rn gravity parameters (rc, the characteristic radius, i.e. the scalelength depending on the gravitating system properties; and β, the universal constant) on stellar dynamics and investigate their constraints from the observed S-star orbits. The presented results show that these observations could put reliable constraints on the parameters of Rn gravity.
T2  - Astronomical and Astrophysical Transactions
T1  - Rn gravity as a viable alternative to dark matter: Application to stellar dynamics
VL  - 30
IS  - 3
SP  - 351
EP  - 358
UR  - https://hdl.handle.net/21.15107/rcub_vinar_7781
ER  - 

@article{
author = "Borka Jovanović, Vesna and Jovanović, Predrag and Borka, Duško and Capozziello, Salvatore",
year = "2018",
abstract = "The role of f(R) gravity, as well as the other modifications of standard Einstein’s gravity, is to explain the accelerated expansion, structure formation of the Universe, and some other phenomena at extragalactic scales (such as e.g. flat rotation curves of spiral galaxies) without adding unknown forms of dark energy or dark matter. In f(R) model, the Ricci scalar in the Einstein–Hilbert action is replaced by a general function of it. Its power-law form Rn is analyzed here using observed orbits of S-stars around the Galactic Center and also their computer simulations. We review the various consequences of the Rn gravity parameters (rc, the characteristic radius, i.e. the scalelength depending on the gravitating system properties; and β, the universal constant) on stellar dynamics and investigate their constraints from the observed S-star orbits. The presented results show that these observations could put reliable constraints on the parameters of Rn gravity.",
journal = "Astronomical and Astrophysical Transactions",
title = "Rn gravity as a viable alternative to dark matter: Application to stellar dynamics",
volume = "30",
number = "3",
pages = "351-358",
url = "https://hdl.handle.net/21.15107/rcub_vinar_7781"
}

Borka Jovanović, V., Jovanović, P., Borka, D.,& Capozziello, S.. (2018). Rn gravity as a viable alternative to dark matter: Application to stellar dynamics. in Astronomical and Astrophysical Transactions, 30(3), 351-358.
https://hdl.handle.net/21.15107/rcub_vinar_7781

Borka Jovanović V, Jovanović P, Borka D, Capozziello S. Rn gravity as a viable alternative to dark matter: Application to stellar dynamics. in Astronomical and Astrophysical Transactions. 2018;30(3):351-358.
https://hdl.handle.net/21.15107/rcub_vinar_7781 .

Borka Jovanović, Vesna, Jovanović, Predrag, Borka, Duško, Capozziello, Salvatore, "Rn gravity as a viable alternative to dark matter: Application to stellar dynamics" in Astronomical and Astrophysical Transactions, 30, no. 3 (2018):351-358,
https://hdl.handle.net/21.15107/rcub_vinar_7781 .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Jovanović, Predrag
AU  - Borka, Duško
AU  - Capozziello, Salvatore
PY  - 2018
UR  - http://www.mdpi.com/2218-2004/7/1/4
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/8218
AB  - The global properties of elliptical galaxies are connected through the so-called fundamental plane of ellipticals, which is an empirical relation between their parameters: effective radius, central velocity dispersion and mean surface brightness within the effective radius. We investigated the relation between the parameters of the fundamental plane equation and the parameters of modified gravity potential f ( R ) . With that aim, we compared theoretical predictions for circular velocity in f ( R ) gravity with the corresponding values from a large sample of observed elliptical galaxies. Besides, we consistently reproduced the values of coefficients of the fundamental plane equation as deduced from observations, showing that the photometric quantities like mean surface brightness are related to gravitational parameters. We show that this type of modified gravity, especially its power-law version— R n , is able to reproduce the stellar dynamics in elliptical galaxies. In addition, it is shown that R n gravity fits the observations very well, without the need for a dark matter.
T2  - Atoms
T1  - Fundamental Plane of Elliptical Galaxies in f(R) Gravity: The Role of Luminosity
VL  - 7
IS  - 1
SP  - 4
DO  - 10.3390/atoms7010004
ER  - 

@article{
author = "Borka Jovanović, Vesna and Jovanović, Predrag and Borka, Duško and Capozziello, Salvatore",
year = "2018",
abstract = "The global properties of elliptical galaxies are connected through the so-called fundamental plane of ellipticals, which is an empirical relation between their parameters: effective radius, central velocity dispersion and mean surface brightness within the effective radius. We investigated the relation between the parameters of the fundamental plane equation and the parameters of modified gravity potential f ( R ) . With that aim, we compared theoretical predictions for circular velocity in f ( R ) gravity with the corresponding values from a large sample of observed elliptical galaxies. Besides, we consistently reproduced the values of coefficients of the fundamental plane equation as deduced from observations, showing that the photometric quantities like mean surface brightness are related to gravitational parameters. We show that this type of modified gravity, especially its power-law version— R n , is able to reproduce the stellar dynamics in elliptical galaxies. In addition, it is shown that R n gravity fits the observations very well, without the need for a dark matter.",
journal = "Atoms",
title = "Fundamental Plane of Elliptical Galaxies in f(R) Gravity: The Role of Luminosity",
volume = "7",
number = "1",
pages = "4",
doi = "10.3390/atoms7010004"
}

Borka Jovanović, V., Jovanović, P., Borka, D.,& Capozziello, S.. (2018). Fundamental Plane of Elliptical Galaxies in f(R) Gravity: The Role of Luminosity. in Atoms, 7(1), 4.
https://doi.org/10.3390/atoms7010004

Borka Jovanović V, Jovanović P, Borka D, Capozziello S. Fundamental Plane of Elliptical Galaxies in f(R) Gravity: The Role of Luminosity. in Atoms. 2018;7(1):4.
doi:10.3390/atoms7010004 .

Borka Jovanović, Vesna, Jovanović, Predrag, Borka, Duško, Capozziello, Salvatore, "Fundamental Plane of Elliptical Galaxies in f(R) Gravity: The Role of Luminosity" in Atoms, 7, no. 1 (2018):4,
https://doi.org/10.3390/atoms7010004 . .

TY  - JOUR
AU  - Capozziello, Salvatore
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
AU  - Borka, Duško
PY  - 2017
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/1696
AB  - We demonstrate that the existence of a Noether symmetry in f theories of gravity gives rise to a further gravitational radius, besides tile standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Fully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis.
T2  - Journal of Cosmology and Astroparticle Physics
T1  - Addressing the missing matter problem in galaxies through a new fundamental gravitational radius
IS  - 6
DO  - 10.1088/1475-7516/2017/06/044
ER  - 

@article{
author = "Capozziello, Salvatore and Jovanović, Predrag and Borka Jovanović, Vesna and Borka, Duško",
year = "2017",
abstract = "We demonstrate that the existence of a Noether symmetry in f theories of gravity gives rise to a further gravitational radius, besides tile standard Schwarzschild one, determining the dynamics at galactic scales. By this feature, it is possible to explain the baryonic Fully-Fisher relation and the rotation curve of gas-rich galaxies without the dark matter hypothesis.",
journal = "Journal of Cosmology and Astroparticle Physics",
title = "Addressing the missing matter problem in galaxies through a new fundamental gravitational radius",
number = "6",
doi = "10.1088/1475-7516/2017/06/044"
}

Capozziello, S., Jovanović, P., Borka Jovanović, V.,& Borka, D.. (2017). Addressing the missing matter problem in galaxies through a new fundamental gravitational radius. in Journal of Cosmology and Astroparticle Physics(6).
https://doi.org/10.1088/1475-7516/2017/06/044

Capozziello S, Jovanović P, Borka Jovanović V, Borka D. Addressing the missing matter problem in galaxies through a new fundamental gravitational radius. in Journal of Cosmology and Astroparticle Physics. 2017;(6).
doi:10.1088/1475-7516/2017/06/044 .

Capozziello, Salvatore, Jovanović, Predrag, Borka Jovanović, Vesna, Borka, Duško, "Addressing the missing matter problem in galaxies through a new fundamental gravitational radius" in Journal of Cosmology and Astroparticle Physics, no. 6 (2017),
https://doi.org/10.1088/1475-7516/2017/06/044 . .

TY  - JOUR
AU  - Borka Jovanović, Vesna
AU  - Capozziello, Salvatore
AU  - Jovanović, Predrag
AU  - Borka, Duško
PY  - 2016
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/1408
AB  - The fundamental plane (FP) of galaxies can be recovered in the framework of f (R) gravity avoiding the issues related to dark matter to fit the observations. In particular, the power-law version f (R) proportional to R-n, resulting from the existence of Noether symmetries for f (R), is sufficient to implement the approach. In fact, relations between the FP parameters and the corrected Newtonian potential, coming from Rn, can be found and justified from a physical point of view. Specifically, we analyze the velocity distribution of elliptical galaxies and obtain that r(c), the scale-length depending on the gravitational system properties, is proportional to re, the galaxy effective radius. This fact points out that the gravitational corrections induced by f (R) can lead photometry and dynamics of the system. Furthermore, the main byproduct of such an approach is that gravity could work in different ways depending on the scales of self-gravitating systems. (C) 2016 Elsevier B.V. All rights reserved.
T2  - Physics of the Dark Universe
T1  - Recovering the fundamental plane of galaxies by f (R) gravity
VL  - 14
SP  - 73
EP  - 83
DO  - 10.1016/j.dark.2016.10.003
ER  - 

@article{
author = "Borka Jovanović, Vesna and Capozziello, Salvatore and Jovanović, Predrag and Borka, Duško",
year = "2016",
abstract = "The fundamental plane (FP) of galaxies can be recovered in the framework of f (R) gravity avoiding the issues related to dark matter to fit the observations. In particular, the power-law version f (R) proportional to R-n, resulting from the existence of Noether symmetries for f (R), is sufficient to implement the approach. In fact, relations between the FP parameters and the corrected Newtonian potential, coming from Rn, can be found and justified from a physical point of view. Specifically, we analyze the velocity distribution of elliptical galaxies and obtain that r(c), the scale-length depending on the gravitational system properties, is proportional to re, the galaxy effective radius. This fact points out that the gravitational corrections induced by f (R) can lead photometry and dynamics of the system. Furthermore, the main byproduct of such an approach is that gravity could work in different ways depending on the scales of self-gravitating systems. (C) 2016 Elsevier B.V. All rights reserved.",
journal = "Physics of the Dark Universe",
title = "Recovering the fundamental plane of galaxies by f (R) gravity",
volume = "14",
pages = "73-83",
doi = "10.1016/j.dark.2016.10.003"
}

Borka Jovanović, V., Capozziello, S., Jovanović, P.,& Borka, D.. (2016). Recovering the fundamental plane of galaxies by f (R) gravity. in Physics of the Dark Universe, 14, 73-83.
https://doi.org/10.1016/j.dark.2016.10.003

Borka Jovanović V, Capozziello S, Jovanović P, Borka D. Recovering the fundamental plane of galaxies by f (R) gravity. in Physics of the Dark Universe. 2016;14:73-83.
doi:10.1016/j.dark.2016.10.003 .

Borka Jovanović, Vesna, Capozziello, Salvatore, Jovanović, Predrag, Borka, Duško, "Recovering the fundamental plane of galaxies by f (R) gravity" in Physics of the Dark Universe, 14 (2016):73-83,
https://doi.org/10.1016/j.dark.2016.10.003 . .

TY  - JOUR
AU  - Borka, Duško
AU  - Capozziello, Salvatore
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
PY  - 2016
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/1070
AB  - We consider possible signatures for the so called hybrid gravity within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed a la Palatini and can be easily reduced to an equivalent scalar-tensor theory. Such an approach is introduced in order to cure the shortcomings related to f(R) gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Center where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter phi(0), showing that in the case of S2 star it is between -0.0009 and -0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter m(phi), and found that it is between -0.0034 and -0.0025 AU(-1) for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law f(R)proportional to R-n gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales. (C) 2016 Elsevier B.V. All rights reserved.
PB  - Elsevier
T2  - Astroparticle Physics
T1  - Probing hybrid modified gravity by stellar motion around Galactic Center
VL  - 79
SP  - 41
EP  - 48
DO  - 10.1016/j.astropartphys.2016.03.002
ER  - 

@article{
author = "Borka, Duško and Capozziello, Salvatore and Jovanović, Predrag and Borka Jovanović, Vesna",
year = "2016",
abstract = "We consider possible signatures for the so called hybrid gravity within the Galactic Central Parsec. This modified theory of gravity consists of a superposition of the metric Einstein-Hilbert Lagrangian with an f(R) term constructed a la Palatini and can be easily reduced to an equivalent scalar-tensor theory. Such an approach is introduced in order to cure the shortcomings related to f(R) gravity, in general formulated either in metric or in metric-affine frameworks. Hybrid gravity allows to disentangle the further gravitational degrees of freedom with respect to those of standard General Relativity. The present analysis is based on the S2 star orbital precession around the massive compact dark object at the Galactic Center where the simulated orbits in hybrid modified gravity are compared with astronomical observations. These simulations result with constraints on the range of hybrid gravity interaction parameter phi(0), showing that in the case of S2 star it is between -0.0009 and -0.0002. At the same time, we are also able to obtain the constraints on the effective mass parameter m(phi), and found that it is between -0.0034 and -0.0025 AU(-1) for S2 star. Furthermore, the hybrid gravity potential induces precession of S2 star orbit in the same direction as General Relativity. In previous papers, we considered other types of extended gravities, like metric power law f(R)proportional to R-n gravity, inducing Yukawa and Sanders-like gravitational potentials, but it seems that hybrid gravity is the best among these models to explain different gravitational phenomena at different astronomical scales. (C) 2016 Elsevier B.V. All rights reserved.",
publisher = "Elsevier",
journal = "Astroparticle Physics",
title = "Probing hybrid modified gravity by stellar motion around Galactic Center",
volume = "79",
pages = "41-48",
doi = "10.1016/j.astropartphys.2016.03.002"
}

Borka, D., Capozziello, S., Jovanović, P.,& Borka Jovanović, V.. (2016). Probing hybrid modified gravity by stellar motion around Galactic Center. in Astroparticle Physics
Elsevier., 79, 41-48.
https://doi.org/10.1016/j.astropartphys.2016.03.002

Borka D, Capozziello S, Jovanović P, Borka Jovanović V. Probing hybrid modified gravity by stellar motion around Galactic Center. in Astroparticle Physics. 2016;79:41-48.
doi:10.1016/j.astropartphys.2016.03.002 .

Borka, Duško, Capozziello, Salvatore, Jovanović, Predrag, Borka Jovanović, Vesna, "Probing hybrid modified gravity by stellar motion around Galactic Center" in Astroparticle Physics, 79 (2016):41-48,
https://doi.org/10.1016/j.astropartphys.2016.03.002 . .

TY  - JOUR
AU  - Capozziello, Salvatore
AU  - Borka, Duško
AU  - Jovanović, Predrag
AU  - Borka Jovanović, Vesna
PY  - 2014
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/55
AB  - We investigate the possibility of explaining theoretically the observed deviations of S2 star orbit around the Galactic Centre using gravitational potentials derived from modified gravity models in the absence of dark matter. To this aim, an analytic fourth-order theory of gravity, nonminimally coupled with a massive scalar field, is considered. Specifically, the interaction term is given by the analytic functions f(R) and f(R, phi) where R is the Ricci scalar and phi is a scalar field whose meaning can be related to further gravitational degrees of freedom. We simulate the orbit of the S2 star around the Galactic Centre in f(R) (Yukawa-like) and f(R, phi) (Sanders-like) gravity potentials and compare it with New Technology Telescope/Very Large Telescope observations. Our simulations result in strong constraints on the range of gravity interaction. In the case of analytic functions f(R), we are not able to obtain reliable constraints on the derivative constants f(1) and f(2), because the current observations of the S2 star indicated that they may be highly mutually correlated. In the case of analytic functions f(R, phi), we are able to obtain reliable constraints on the derivative constants f(0), f(R), f(RR), f(phi), f(phi phi), and f(phi R). The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around the Galactic Centre.
T2  - Physical Review D
T1  - Constraining extended gravity models by S2 star orbits around the Galactic Centre
VL  - 90
IS  - 4
DO  - 10.1103/PhysRevD.90.044052
ER  - 

@article{
author = "Capozziello, Salvatore and Borka, Duško and Jovanović, Predrag and Borka Jovanović, Vesna",
year = "2014",
abstract = "We investigate the possibility of explaining theoretically the observed deviations of S2 star orbit around the Galactic Centre using gravitational potentials derived from modified gravity models in the absence of dark matter. To this aim, an analytic fourth-order theory of gravity, nonminimally coupled with a massive scalar field, is considered. Specifically, the interaction term is given by the analytic functions f(R) and f(R, phi) where R is the Ricci scalar and phi is a scalar field whose meaning can be related to further gravitational degrees of freedom. We simulate the orbit of the S2 star around the Galactic Centre in f(R) (Yukawa-like) and f(R, phi) (Sanders-like) gravity potentials and compare it with New Technology Telescope/Very Large Telescope observations. Our simulations result in strong constraints on the range of gravity interaction. In the case of analytic functions f(R), we are not able to obtain reliable constraints on the derivative constants f(1) and f(2), because the current observations of the S2 star indicated that they may be highly mutually correlated. In the case of analytic functions f(R, phi), we are able to obtain reliable constraints on the derivative constants f(0), f(R), f(RR), f(phi), f(phi phi), and f(phi R). The approach we are proposing seems to be sufficiently reliable to constrain the modified gravity models from stellar orbits around the Galactic Centre.",
journal = "Physical Review D",
title = "Constraining extended gravity models by S2 star orbits around the Galactic Centre",
volume = "90",
number = "4",
doi = "10.1103/PhysRevD.90.044052"
}

Capozziello, S., Borka, D., Jovanović, P.,& Borka Jovanović, V.. (2014). Constraining extended gravity models by S2 star orbits around the Galactic Centre. in Physical Review D, 90(4).
https://doi.org/10.1103/PhysRevD.90.044052

Capozziello S, Borka D, Jovanović P, Borka Jovanović V. Constraining extended gravity models by S2 star orbits around the Galactic Centre. in Physical Review D. 2014;90(4).
doi:10.1103/PhysRevD.90.044052 .

Capozziello, Salvatore, Borka, Duško, Jovanović, Predrag, Borka Jovanović, Vesna, "Constraining extended gravity models by S2 star orbits around the Galactic Centre" in Physical Review D, 90, no. 4 (2014),
https://doi.org/10.1103/PhysRevD.90.044052 . .