This article explores traversable wormhole geometries obtained in the context of the symmetric teleparallel gravity theory and highlights their distinctive physical characteristics. Our methodology involves determining the tidal force by employing a specified form of the shape function along with an appropriate equation of state for Case I. In order to extract the shape functions associated with the wormhole solution, we apply the null-complexity condition with tidal force in Case II. In Case III, we utilize the balancing Tolman–Oppenheimer–Volkoff equation in conjunction with a tidal force to obtain viable wormhole shape function. The analysis focuses on the dependence of wormhole characteristics on the parameter $$\zeta $$ . The energy conditions are examined within their respective validity domains for various ranges of the model parameters. We also calculate, the volume integral quantifier, the extent of exotic matter needed to uphold the traversable wormhole structure. Through the effective potential for timelike geodesics, the influence of angular momentum on trajectories is clarified, and the corresponding deflection angle evaluation points to significant light bending close to the throat. By introducing small radial perturbations around the equilibrium shell radius, we examine the stability characteristics for all considered shape functions.

India

Sweeti Kiroriwal

Oman

Azerbaijan

S. Maurya

Jitendra Kumar

Wormhole solutions under tidal force constraints in $\textit{f}$($\textit{Q}$) gravity: a unified approach

In the present work, we incorporate redshift space distortion measurement to investigate the growth of large scale structure within the framework of multi-fluid cosmology in the context of $\textit{f}$($\textit{G}$) gravity. Using 3 different $\textit{f}$($\textit{G}$) gravity models, where $\textit{f}$($\textit{G}$) is the function of Gauss–Bonnet invariant, we compare the predictions of $\textit{f}$($\textit{G}$) gravity expansion history—through the Friedmann equation with Hubble data, BAO data sets and constrain models parameters such as $$\Omega _{m}$$ and $$H_{0}$$ . Within the context of multi-fluid cosmology in $\textit{f}$($\textit{G}$) gravity, we obtain the structure growth equation. This equation is then combined with $$\sigma _{8}$$ to get $$f\sigma _{8}$$ predictions—which is compared with redshift space distortion data to constrain models parameters to obtain best-fit values including $$\sigma _{8}$$ . This involves performing a Markov Chain Monte Carlo (MCMC) analysis for these specific forms of $\textit{f}$($\textit{G}$) models. we also perform a statistical analysis incorporating the Akaike Information Criterion (AIC), the Bayesian Information Criterion (BIC), to assess the goodess-of-fit of the considered models.

Praveen Dhankar

Rwanda

Albert Munyeshyaka

Aritra Sanyal

Saudi Arabia

Safiqul Islam

Farook Rahaman

Constraints on multi-fluid cosmology in $\textit{f}$($\textit{G}$) gravity with different observational data sets

We investigate the velocity-dependent one-scale model to the case of one cosmic F-string and two D-strings as color flux tubes in pure Spin(<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4</mn><mi>N</mi></math>) gauge theory. We analytically calculate the scaling string density as a function of the reconnection probabilities, and confirm our results with numerical calculations. We also determine the timescale at which the string density reaches the scaling regime, and find that for certain values of the reconnection probability, the scaling time can become extremely large, by many orders of magnitude. This leads to a characteristic suppression signature of the gravitational-wave signal at high frequencies, which may become observable in the frequency range of future interferometric gravitational-wave observations.

Japan

Kazuto Nakamura

Masaki Yamada

Delayed scaling of multitype cosmic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>F</mi></math>- and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math>-strings in velocity-dependent one-scale models

In this work, we investigate exact black string solutions in the context of $\textit{f}$($\textit{R}$, $\textit{T}$) gravity. Adopting the specific form $$f(R,T) = R + 2\chi T$$ , we consider an anisotropic Kiselev fluid as the matter content and obtain static cylindrical solutions, which are then extended to the rotating case through a suitable coordinate transformation. The influence of the quintessence state parameter $$w_q$$ and the matter–geometry coupling constant $$\chi $$ on the geometry is analyzed. We examine the weak, null, and strong energy conditions, identifying the regions in the parameter space where they are satisfied. Furthermore, we apply the Hamilton–Jacobi method to study the tunneling of scalar particles across the event horizon and derive the corresponding Hawking temperature. The thermodynamic stability of the solutions is investigated by computing the heat capacity, and the conditions for phase transitions are discussed. The results provide a characterization of black strings in $\textit{f}$($\textit{R}$, $\textit{T}$) gravity surrounded by quintessence, highlighting the combined effects of anisotropic matter and modified gravity on their physical properties.

Brazil

L. Santos

L. Barbosa

C. Barros

Kiselev black strings in $\textit{f}$($\textit{R}$, $\textit{T}$) gravity

This research paper explores the structure of hypothetical compact stars, known as strange stars, within the framework of a novel modified theory of gravity called $$f(R,\Sigma ,T)$$ gravity. This theory extends General Relativity by making gravity dependent not only on the Ricci curvature scalar $\textit{R}$ but also on a torsion scalar $$\Sigma $$ and the trace of the matter energy–momentum tensor $\textit{T}$. This introduces a richer coupling between geometry and matter. The study presents a highly exotic, multi-layered stellar model composed of five distinct regions, each with a unique equation of state and geometric properties. The model features a dark-energy-like core with powerful repulsive gravity (anti-gravity), surrounded by successive layers of dust, exotic radiation, and a stiff matter crust, all enveloped by a standard Schwarzschild vacuum exterior. A key finding is the prevalence of negative energy densities and pressures in several layers, a hallmark of exotic matter. These configurations, enabled by the $$f(R,\Sigma ,T)$$ framework, lead to repulsive gravitational effects that radically alter the star’s internal equilibrium. The analysis demonstrates how additional geometry-driven forces within this theory can support such exotic structures, potentially preventing gravitational collapse and resulting in a stable, non-singular object. This work demonstrates that $$f(R,\Sigma ,T)$$ gravity allows for new and complex classes of compact objects with stratified, exotic matter distributions, whose properties and observational signatures would differ significantly from those predicted by standard General Relativity.

Egypt

M. Bakry

A. Eid

Tahia Dabash

The impact of $$f(R,\Sigma ,T)$$ gravity on strange star structure

In this study, we analyze $\textit{f}$($\textit{R}$) gravity employing the $$ f(R) = R+ \alpha _1 R^p - \alpha _2 R^{-q} $$ model within the Friedmann–Lemaître–Robertson–Walker (FLRW) background. We derive the Friedmann equations via modified gravity action and subsequently reexpress them in terms of the standard Friedmann equations. Our investigation explores the behavior of a bouncing cosmological model within this modified gravity context, offering a potential solution to the singularity problem encountered in the standard Big Bang cosmology. We represent cosmological parameters as functions of cosmic time and scrutinize the conditions for a cosmic bounce. Additionally, we reconstruct the $\textit{f}$($\textit{R}$) gravity model using the redshift parameter and graphically present cosmological parameters as functions of redshift. These plots reveal an accelerated nature of Universe expansion. Furthermore, we reconstruct $\textit{f}$($\textit{R}$) gravity models for scale factors, $$a(t) = e^{e^{\lambda t}}$$ which exhibits the bouncing behavior. Finally, we investigated the stability scenario by examining the sound speed. The resulting graph of sound speed plotted against redshift confirms late-time stability.

Pakistan

M. Ilyas

Khalid Masood

South Korea

Nehad Shah

Dynamical analysis of bouncing cosmology in the Capozziello–De Laurentis model of $\textit{f}$($\textit{R}$) gravity

Tensor-polarized twist-3 parton distribution functions (PDFs) <italic>f<inf>LT</inf></italic>( <italic>x</italic>) are calculated for the spin-1 deuteron by using twist-2 relations, which are similar to the Wandzura-Wilczek relation and the Burkhardt-Cottingham sum rule in the spin-1/2 nucleon, together with tensor-polarized twist-2 PDFs <italic>f</italic> <inf>1<italic>LL</italic></inf>( <italic>x</italic>). The PDFs are shown for <italic>f<inf>LT</inf></italic>( <italic>x</italic>) at <math altimg='si1.svg'><mrow><msup><mi>Q</mi><mn>2</mn></msup><mo linebreak='goodbreak'>=</mo><mn>2.5</mn></mrow></math>&#8239;GeV 2, where the tensor-polarized PDFs <italic>f</italic> <inf>1<italic>LL</italic></inf>( <italic>x</italic>) are provided. The <italic>x</italic>-dependence of <italic>f<inf>LT</inf></italic>( <italic>x</italic>) is similar to <italic>f</italic> <inf>1<italic>LL</italic></inf>( <italic>x</italic>), and the magnitude of <italic>f<inf>LT</inf></italic>( <italic>x</italic>) is roughly of the order of <italic>f</italic> <inf>1<italic>LL</italic></inf>( <italic>x</italic>). In experiments at the Thomas Jefferson National Accelerator Facility (JLab), higher-twist effects could be sizable because <italic>Q</italic> 2 values are not very large in comparison with the hadronic scale of 1&#8239;GeV 2. Therefore, the JLab experiments could provide a good opportunity to investigate the twist-3 distributions <italic>f<inf>LT</inf></italic>( <italic>x</italic>) in addition to the twist-2 ones <italic>f</italic> <inf>1<italic>LL</italic></inf>( <italic>x</italic>). Furthermore, these tensor-polarized PDFs could be investigated at future Electron-Ion Colliders (EICs) and hadron accelerator facilities such as the Fermi National Accelerator Laboratory (Fermilab), the Nuclotron-based Ion Collider fAcility (NICA), and the Large Hadron Collider (LHC).

China

S. Kumano

Kenshi Kuroki

Tensor-polarized twist-3 parton distribution functions <italic>f<inf>LT</inf></italic>( <italic>x</italic>) for the spin-1 deuteron by using twist-2 relations

The aim of this paper is to investigate the stability and existence of the closed Einstein Universe (EU) under linear homogeneous perturbations within the framework of $$ f(\mathcal {R}, \phi , \chi ) $$ gravity. For this, we consider a closed Friedmann–Roberson–Walker universe filled with isotropic matter. Perturbations are imposed on the matter parameters and on the scale factor. We systematically derive the static and perturbed field equations for scenarios with and without conservation of the energy–momentum tensor and examine the associated stability regions through selected models in $$f(\mathcal {R},\phi ,\chi )$$ gravity. The graphical analysis shows that for suitable choices of model parameters such as $$ \alpha $$ , $\textit{b}$ and scalar field $$\phi _o$$ , the stable regions of the Einstein universe can be obtained in this theory of gravity. Significant differences in stability regions are observed for scalar fields governed by standard kinetic energy and for those characterized by negative kinetic energy. The scalar field and coupling parameters play a key role in the existence of stable regions of the Einstein universe.

 Muhammad

M. Azam

A perturbative approach on the stability of the Einstein universe in $$f(\mathcal {R},\phi ,\chi )$$ gravity

In this work, we explore the formulation of the Misner-Sharp energy within the framework of <math altimg='si3.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>)</mo></mrow></math> gravity, a modified theory incorporating the Ricci scalar <italic>R</italic> and the Gauss-Bonnet scalar <math altimg='si4.svg'><mi mathvariant='script'>G</mi></math>. By extending the quasilocal energy definition to both static spherically symmetric spacetime and the dynamic Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime, we derive explicit expressions for the generalized Misner-Sharp energy using two complementary approaches: the integration method and the conserved charge method based on the Kodama vector. Our analysis shows that the Misner-Sharp energy expression in <math altimg='si3.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>)</mo></mrow></math> gravity reduces to standard <italic>f</italic>( <italic>R</italic>) gravity results when the Gauss-Bonnet term is absent, revealing how curvature modifications influence the geometric structure and dynamics of cosmic evolution. Furthermore, we investigate the thermodynamic properties at the apparent horizon associated with the FLRW background, and we find a connection to non-equilibrium thermodynamics unique to <math altimg='si3.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>)</mo></mrow></math> gravity. These findings underscore the subtle and fundamental role of curvature corrections in determining the energy distribution and thermodynamic behavior of gravitational systems.

Iran

Türkiye

Amin Rezaei Akbarieh

Navid Safarzadeh Ilkhchi

Yaghoub Heydarzade

Generalized Misner-Sharp energy in <math altimg='si3.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi mathvariant='script'>G</mi><mo>)</mo></mrow></math> gravity

This work investigates a modified theory of gravity where the Einstein-Hilbert action, including a cosmological constant, is non-minimally coupled to a Yang-Mills field via an <math altimg='si1.svg'><mrow><msup><mi>R</mi><mn>3</mn></msup><msubsup><mi>F</mi><mrow><mi>&#956;</mi><mi>&#945;</mi></mrow><mrow><mo>(</mo><mi>a</mi><mo>)</mo></mrow></msubsup><msup><mi>F</mi><mrow><mo>(</mo><mi>a</mi><mo>)</mo><mi>&#956;</mi><mi>&#945;</mi></mrow></msup></mrow></math> interaction term. We treat this coupling as the leading higher-derivative correction in a low-energy effective field theory (EFT) deformation of the standard Einstein-Yang-Mills theory. We derive a black brane solution for this model, accurate to the first order in the EFT coupling parameter <italic>q</italic> <inf>2</inf>, and specify the regime of validity <math altimg='si2.svg'><mrow><mfrac><mrow><mrow><mo>|</mo></mrow><msub><mi>q</mi><mn>2</mn></msub><mrow><mo>|</mo></mrow></mrow><msup><mi>L</mi><mn>6</mn></msup></mfrac><mo>&#8810;</mo><mn>1</mn></mrow></math>. Using gauge/gravity duality techniques, we then compute two key holographic transport coefficients: the color non-abelian direct current (DC) conductivity and the ratio of shear viscosity to entropy density. Our analysis reveals that both transport coefficients are modified by the non-minimal coupling, with the conductivity bound violated for positive <italic>q</italic> <inf>2</inf> and the Kovtun-Son-Starinets (KSS) bound for shear viscosity violated for negative <italic>q</italic> <inf>2</inf>. The results are interpreted within the EFT framework, and possible constraints on the sign of <italic>q</italic> <inf>2</inf> from stability and causality are discussed. In the limit where the non-minimal coupling vanishes, our results consistently reduce to those of the standard Yang-Mills Schwarzschild Anti-de Sitter (AdS) black brane.

Mehdi Sadeghi

Holographic aspects of non-minimal <italic>R</italic> 3 <italic>F</italic> 2 black brane in an EFT framework