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Special Issue Editors

Prof. Dr. Branko Dragovich

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Guest Editor

1. Institute of Physics, University of Belgrade, Belgrade, Serbia
2. Mathematical Institute, Serbian Academy of Sciences and Arts, Belgrade, Serbia
Interests: modified gravity; cosmology; p-adic analysis; p-adic mathematical physics; p-adic string theory; genetic code and bioinformation
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Prof. Dr. Dejan Stojkovic

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Guest Editor

Department of Physics, SUNY at Buffalo, Buffalo, NY 14260-1500, USA
Interests: cosmology; general relativity; particle physics; field theory; extra dimensions; brane world models; beyond the standard model phenomenology

Special Issue Information

Dear Colleagues,

We are pleased to announce a Special Issue of Symmetry, titled "Modified Gravity and Related Symmetries", and invite you to contribute your research to this exciting collection.

Despite its tremendous success, Einstein's general relativity is not free of shortcomings. The study of modified gravity theories has recently become a cornerstone of modern theoretical physics, offering profound insights into the nature of spacetime, cosmology, and the fundamental symmetries which underpin our understanding of the universe. This Special Issue aims to explore the interplay between modified gravity theories and the symmetries that govern them, including but not limited to Lorentz invariance, diffeomorphism invariance, de Sitter invariance, Anti de Sitter invariance, scale invariance, etc.

We welcome contributions that address both theoretical developments and observational implications of modified gravity, as well as their connections to symmetry principles. We encourage submissions of original research articles, reviews, and perspectives that advance our understanding of these topics.

Topics of Interest:

Modified theories of gravity (e.g., non-local gravity, f(R), f(T), scalar–tensor theories, Horndeski gravity, etc.);
Symmetries in gravitational theories and their breaking;
Noether symmetries and conservation laws in modified gravity;
Cosmological implications of modified gravity and symmetry principles;
Black hole solutions and their symmetries in alternative gravity theories;
Quantum gravity, string theory, and symmetry considerations;
Observational tests of modified gravity and their relation to symmetries;
Mathematical foundations of symmetries in gravitational physics.

Prof. Dr. Branko Dragovich
Prof. Dr. Dejan Stojkovic
Guest Editors

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Published Papers (2 papers)

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Research

12 pages, 299 KB

Open AccessArticle

On the Physical Nature of the Scalar Mode Mass in the Jordan Frame of Metric f(R) Gravity

by Giovanni Montani and Andrea Valletta

Symmetry 2026, 18(5), 714; https://doi.org/10.3390/sym18050714 - 23 Apr 2026

Viewed by 226

Abstract

We analyze the Taylor expansion of the metric

f (R)

gravity in the Jordan frame around the General Relativity limit, expanding in the small deviation

(ϕ - ϕ_{0})

with

ϕ_{0} = 1

. By relating the scalar–tensor [...] Read more.

We analyze the Taylor expansion of the metric

f (R)

gravity in the Jordan frame around the General Relativity limit, expanding in the small deviation

(ϕ - ϕ_{0})

with

ϕ_{0} = 1

. By relating the scalar–tensor representation to the original

f (R)

formulation, we derive constraints on the expansion parameters from the observed value of the present-day

Λ

CDM (

Λ

Cold Dark Matter) deceleration parameter and from cosmological bounds on the variation of Newton’s constant. We show that these requirements imply that the scalar degree of freedom must have a mass exceeding the Hubble scale by several orders of magnitude. This result challenges the common assumption that the scalar mode can drive cosmological dynamics with a mass of order of the Hubble constant

H_{0}

. We provide a dynamical interpretation of this hierarchy by emphasizing that a proper definition of the scalar mass, in a field-theoretical sense, requires an adiabatic separation between background evolution and perturbations, which naturally leads to a super-Hubble mass scale. Full article

(This article belongs to the Special Issue Modified Gravity and Related Symmetries)

19 pages, 1178 KB

Open AccessArticle

Constraints on a Fifth Force from the Stellar Orbits Around the Central Supermassive Black Hole of the Milky Way

by Predrag Jovanović, Duško Borka and Vesna Borka Jovanović

Symmetry 2026, 18(4), 557; https://doi.org/10.3390/sym18040557 - 25 Mar 2026

Viewed by 642

Abstract

Here we investigate a possible presence of a fifth force at the Galactic Center (GC), and its potential influence on the stellar orbits around the central supermassive black hole (SMBH) of our Galaxy. For this purpose we simulated the stellar orbits in a Yukawa gravity model that predicts the emergence of a fifth force, and fitted them into the observed orbit of S2 star around Sgr A* at the GC. The fitting was performed using Markov chain Monte Carlo (MCMC) method which enabled us to constrain the parameters of Yukawa interaction describing the strength

δ

and the range

λ

of a fifth force. We studied the following cases for a fifth force range

λ

: (i) when it is about a few hundred AU (i.e., deep inside the orbit of S2 star), (ii) when it is about a thousand AU (i.e., approximately the size of S2 star orbit), and (iii) when it is several thousand AU (i.e., much larger than the size of S2 star orbit). The obtained results showed that as the range

λ

of a fifth force increases, its strength

δ

also increases and relative error

Δ δ / δ

decreases. The resulting fifth-force strengths in all three cases are respectively:

δ

∼0.005, 0.02 and 0.15. These results are consistent with the corresponding results of both our previous studies and those of other authors, regardless of the different Yukawa-like potentials used to model a fifth force. In addition, assuming that the orbital precession of S2 star is close to the prediction of General Relativity (GR) for its Schwarzschild precession, we studied whether the possible small discrepancies from this prediction could be also caused by a fifth force. For this purpose we used the

f_{SP}

parameter that was recently measured in the case of S2 star by GRAVITY Collaboration in 2020, and that describes the extent to which some gravitational model is relativistic. We found that the obtained estimates in all three cases are compatible, within the error intervals, with the measured value of

f_{SP} = 1.10 \pm 0.19

. Full article

(This article belongs to the Special Issue Modified Gravity and Related Symmetries)

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