In this work, we explore a cosmological model within the framework of modified gravity, specifically a logarithmic form of $\textit{f}$($\textit{Q}$) gravity. Using recent observational datasets including RSD and DESI, we constrain the model parameters via Markov Chain Monte Carlo (MCMC) techniques. Our analysis focuses on both background and perturbation-level cosmological diagnostics, evaluating the evolution of cosmographic parameters and the growth rate of structure through $$f\sigma _8$$ . The results demonstrate consistency with observational data, particularly supporting a quintessence-like accelerated expansion. Additionally, the model addresses the $$S_8$$ tension and provides insights into the late-time behavior of dark energy.

India

L. Sudharani

N. Kavya

V. Venkatesha

Cosmic structure growth and perturbation analysis in logarithmic $\textit{f}$($\textit{Q}$) gravity

We construct an analytic $\textit{f}$($\textit{R}$) gravity model that unifies early-time inflation with late-time cosmic acceleration within a single covariant framework. At high curvature, the model reproduces a Starobinsky-like inflationary plateau, while at low curvature it asymptotes to a stable dark energy-dominated phase. In the scalar-tensor representation, this construction yields a hilltop-type potential in the Jordan frame, which maps to an exponential potential in the Einstein frame. To account for radiative effects, we introduce a logarithmic correction to the Einstein-frame potential inspired by one-loop effective field theory, producing a late-time flattening without requiring fine-tuning. The resulting scalaron dynamics reduce the effective mass to $$\mathcal {O}(H_0)$$ , inducing a thawing regime that deviates from a cosmological constant at the sub-percent levels. A joint background likelihood analysis using Pantheon+SH0ES and BAO+CC datasets (within the CPL parametrization) yields $$H_0 = 73.4 \pm 0.6$$ km/s/Mpc and $$\Omega _m = 0.253 \pm 0.007$$ , consistent with local expansion rate measurements. The best-fit scalar field parameters are $$\varphi _0 \approx 0.027\,M_\textrm{Pl}$$ and $$\lambda \approx 0.010\,M_\textrm{Pl}$$ , corresponding to a present-day dark energy equation of state $$w_0 \approx -0.985$$ . While compatible with $$\Lambda $$ CDM within current observational bounds, the model satisfies GR recovery at low curvature and exhibits attractor-like behavior, thereby minimizing sensitivity to initial conditions.

M. Pradosh Keshav

Arun Kenath

Loop-corrected scalar potentials and late-time acceleration in $$f(R)$$ gravity

<p>Motivated by the recent BESIII Collaboration measurements of the decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>η</mi><mi>η</mi></math>, we investigate this process by considering the contribution from the resonance <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo></math>, which is generated by <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-wave pseudoscalar meson-pseudoscalar meson interaction, and the contribution from the intermediate scalar meson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>1370</mn><mo stretchy="false">)</mo></math>. Our results could give a good description of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>+</mo></msup><mi>η</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi><mi>η</mi></math> invariant mass distributions, which implies that the contribution from the intermediate <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>1370</mn><mo stretchy="false">)</mo></math>, neglected in BESIII analysis, could play a role in this process. Furthermore, the predicted Dalitz plots are also consistent with the BESIII measurements. The more precise measurements about this process in the future could shed light on the mechanism of this process and the properties of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>1370</mn><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo></math>.</p>

China

Wen-Tao Lyu

Le-Le Wei

De-Min Li

En Wang

Hadronic decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mo>+</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><mi>η</mi><mi>η</mi></math> and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>1370</mn><mo stretchy="false">)</mo></math> contributions

We examine inflationary models in the <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo>,</mo><mi>T</mi><mo stretchy='false'>)</mo></math> gravity framework where we have a conformal constant and an <italic>RT</italic>-mixing term apart from an R term. The RT-mixing term introduces non-minimal coupling between gravity and matter. We consider the exponential SUSY potential <math altimg='si2.svg'><mi>V</mi><mo stretchy='false'>(</mo><mi>&#981;</mi><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><msup><mrow><mi>M</mi></mrow><mrow><mn>4</mn></mrow></msup><mrow><mo stretchy='true'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><msup><mrow><mi>e</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>&#955;</mi><mi>&#981;</mi><mo stretchy='false'>/</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>p</mi><mi>l</mi></mrow></msub></mrow></msup><mo stretchy='true'>)</mo></mrow></math> and a novel potential <math altimg='si3.svg'><mi>V</mi><mo stretchy='false'>(</mo><mi>&#981;</mi><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>&#955;</mi><msubsup><mrow><mi>M</mi></mrow><mrow><mi>p</mi><mi>l</mi></mrow><mrow><mn>4</mn><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>2</mn><mi>&#945;</mi></mrow></msubsup><msup><mrow><mi>&#981;</mi></mrow><mrow><mn>2</mn><mi>&#945;</mi></mrow></msup><msup><mrow><mi mathvariant='normal'>sin</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>&#8289;</mo><mrow><mo stretchy='true'>(</mo><mfrac><mrow><mi>&#946;</mi><msubsup><mrow><mi>M</mi></mrow><mrow><mi>p</mi><mi>l</mi></mrow><mrow><mi>&#945;</mi></mrow></msubsup></mrow><mrow><msup><mrow><mi>&#981;</mi></mrow><mrow><mi>&#945;</mi></mrow></msup></mrow></mfrac><mo stretchy='true'>)</mo></mrow></math>. With the help of COBE normalization, we constrain values of different parameters and extract the field value at the time of Hubble crossing. The end of inflation is marked by <math altimg='si4.svg'><msub><mrow><mover accent='true'><mrow><mi>&#1013;</mi></mrow><mrow><mo stretchy='false'>&#732;</mo></mrow></mover></mrow><mrow><mi>v</mi></mrow></msub><mo stretchy='false'>(</mo><msub><mrow><mi>&#981;</mi></mrow><mrow><mi>i</mi></mrow></msub><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>1</mn></math> where <math altimg='si5.svg'><msub><mrow><mi>&#981;</mi></mrow><mrow><mi>i</mi></mrow></msub></math> is the field value at the end of inflation. Equipped with these values, we then move on to calculate values of spectral index <math altimg='si6.svg'><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math> and tensor-to-scalar ratio <italic>r</italic>. Our predicted values of <math altimg='si6.svg'><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math> and <italic>r</italic> fall within their observed values from the Planck 2018 survey and BICEP/Keck array measurement for both potential, making them plausible candidates for the inflationary model. We also display the variation of the tensor-to-scalar ratio and spectral index with the coefficient of RT-mixing term for fixed values of e-fold number. There, we find the existence of two local maxima of <math altimg='si6.svg'><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math>, which occur at a negative and a positive value of <italic>&#958;</italic>, the coefficient of <italic>RT</italic>-mixing term. Our analysis finds a significant impact of <italic>&#958;</italic> on values of observables.

Sohan Kumar Jha

Anisur Rahaman

Non-minimal <italic>RT</italic> coupling and its impact on inflationary evolution in <italic>f</italic>( <italic>R</italic>, <italic>T</italic>) gravity

In this work, we construct a novel exact solution in the framework of symmetric teleparallel gravity (STG), specifically in the context of three-dimensional <math altimg='si31.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> gravity, where <math altimg='si32.svg'><mi mathvariant='double-struck'>Q</mi></math> is the non-metricity scalar. Utilizing a spherically symmetric <math altimg='si30.svg'><mrow><mo>(</mo><mn>2</mn><mo linebreak='goodbreak'>+</mo><mn>1</mn><mo>)</mo></mrow></math>-dimensional metric and the coincident gauge condition, we derive a new class of black hole solutions characterized by an analytic form of <math altimg='si31.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> that generalizes the Banados-Teitelboim-Zanelli (BTZ) solution. The resulting solution generalizes the BTZ black hole by incorporating a dimensional deformation parameter <math altimg='si3.svg'><msub><mi>a</mi><mn>1</mn></msub></math>, yielding deviations from general relativity due to non-metricity corrections. This solution reduces to the standard BTZ geometry in the limit of vanishing deformation parameter <math altimg='si3.svg'><msub><mi>a</mi><mn>1</mn></msub></math>, while exhibiting distinctive features when <math altimg='si33.svg'><mrow><msub><mi>a</mi><mn>1</mn></msub><mo>&#8800;</mo><mn>0</mn></mrow></math>, including deviation in curvature and non-metricity scalars. We conduct a thorough analysis of the thermodynamic properties of the resulting black hole, including its Hawking temperature, entropy, and heat capacity, confirming its thermodynamic stability and demonstrating the validity of the first law of thermodynamics. Furthermore, we explore the topological classification of the black hole using the generalized free energy method, demonstrating the existence of nontrivial topological charges associated with its horizon structure.

South Africa

Egypt

G.G.L. Nashed

M. Bedair

Topology and stability of a <math altimg='si30.svg'><mrow><mo>(</mo><mn>2</mn><mo linebreak='goodbreak'>+</mo><mn>1</mn><mo>)</mo></mrow></math>-dimensional black hole in <math altimg='si31.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> gravity

In this paper, we investigate the viability of an exponential <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>T</mi><mo stretchy='false'>)</mo></math> gravity for describing cosmic inflation with a canonical scalar field. In order to obtain concrete results, we use four well-known potentials such as general hilltop inflation potential, valley hybrid inflation potential, shaft potential and minimal inflation potential. For each considered potential, we evaluate the several inflationary parameters at background and perturbative levels. Then, we perform a Markov Chain Monte Carlo (MCMC) analysis to estimate the parameters of each potential model by exploring its parameter space. In addition, we plot the corresponding trajectories in the <math altimg='si2.svg'><mi>r</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math> and <math altimg='si3.svg'><msub><mrow><mi>&#945;</mi></mrow><mrow><mi>s</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><msub><mrow><mi>n</mi></mrow><mrow><mi>s</mi></mrow></msub></math> planes. In this sense, we make the comparison with the two-marginalized joint confidence at 68% and 95% C.L. from the latest BICEP/Keck results. The results mostly show small values for the tensor -to-scalar ratio and acceptable values for the scalar spectral index, which are within the current observational bounds.

Pakistan

Abdul Jawad

Chile

Nelson Videla

Azerbaijan

Abdul Malik Sultan

Kazakhstan

N. Myrzakulov

Ayesha Aslam

Uzbekistan

Sanjar Shaymatov

Observational constraints on inflationary parameters in exponential <italic>f</italic>( <italic>T</italic>) gravity with well-known potentials

The concept of complexity related to the celestial systems is elaborated within the context of distinct revised gravity theories. However, its interpretation in $\textit{f}$($\textit{R}$, $\textit{G}$) gravity is the main idea of our manuscript. We assume that the inner configuration of the system is a cylindrically symmetric geometry comprising the anisotropic configuration of matter. In our case study, we determine the revised equations of motion combined with the orthogonal decomposition of the Riemann tensor. The implications of anisotropic pressure and nonhomogeneous energy density are relevant. Decisive results relating to the Tolman mass, Weyl scalar, and the complexity factor are derived by incorporating dark source terms corresponding to the $\textit{f}$($\textit{R}$, $\textit{G}$) theory. Additionally, the structure scalars calculated in our manuscript are employed to derive the expression for the complexity factor, after considering reducing the complexity constraint to obtain the solutions for the specific models. The compact structures with anisotropic pressure and non-homogeneous energy density claim the maximum complexity. However, these fluids might not demonstrate any complexity if the implications of non-homogeneous energy density and anisotropic pressure are eradicated because of dark source terms corresponding to the $\textit{f}$($\textit{R}$, $\textit{G}$) theory.

A. Rehman

M. Yousaf

Faisal Javed

Thailand

Phongpichit Channuie

Interpretation of complexity associated with cylindrically symmetric configuration in $\textit{f}$($\textit{R}$, $\textit{G}$) theory

This study explores the influence of test particles in the vicinity of a static, spherically symmetric black hole (BH) within the <math altimg='si1.svg'><mi>F</mi><mo stretchy='false'>(</mo><mi>R</mi><mo stretchy='false'>)</mo></math>-corrected model. The BH solution is illustrated by five parameters: mass <italic>M</italic>, three dimensionless coefficients <italic>a</italic>, <italic>b</italic>, and <italic>c</italic>, and the Planck length <math altimg='si2.svg'><msub><mrow><mi>l</mi></mrow><mrow><mi>p</mi></mrow></msub></math>. Using the effective potential, we show the stability of circular orbits and derive an exact result for the energy and angular momentum (AM) of particles in terms of the BH parameters. We define the innermost stable circular orbits (ISCOs) and examine the effective forces that influence particle trajectories. In addition, we analyze epicyclic oscillations (EO) close to the equatorial plane, providing exact formulas for radial, vertical, and orbital frequencies. The frequency of periastron precession is also evaluated. Furthermore, we investigate particle collisions near the BH horizon, computing the resulting center-of-mass energy (CME). Our results show the role of the model parameters in shaping the dynamics of the particles and their motion properties.

Allah Ditta

Algeria

Abdelmalek Bouzenada

Saudi Arabia

Muneerah Alomar

Mona Bin-Asfour

Dynamics of test particles and quasi-periodic oscillations mathematically around F(R)-corrected black holes

We show that gravitational leptogenesis with dynamical <italic>CPT</italic> breaking in an expanding universe can be reconciled with the exponential <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo stretchy='false'>)</mo></math> gravity model, which introduces only one additional parameter <italic>&#946;</italic> compared to the standard &#923;CDM cosmology. This model incorporated axions as cold dark matter. For <italic>L</italic> violating interactions, we consider both a non-supersymmetric model with heavy right-handed neutrino decay and a supersymmetric model with sneutrino decay. For both cases, we have shown that the required baryonic asymmetry could be obtained. We have also shown the variation of decoupling temperature for lepton number violating interactions with the <italic>&#946;</italic> parameter in exponential <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo stretchy='false'>)</mo></math> gravity. Lepton number-violating model parameters are constrained with the <italic>&#946;</italic> through the decoupling temperature. An upper bound on the <italic>&#946;</italic> parameter of the exponential <math altimg='si1.svg'><mi>f</mi><mo stretchy='false'>(</mo><mi>R</mi><mo stretchy='false'>)</mo></math> gravity is also obtained.

Suhail Khan

Ajay Bassi

Rathin Adhikari

Leptogenesis in exponential <italic>f</italic>( <italic>R</italic>) gravity model

<p>The branching fractions of the axial vector meson decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><msub><mi>a</mi><mn>0</mn></msub><mi>π</mi><mo>,</mo><mi>π</mi><mi>π</mi><mi>η</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mi>ρ</mi><mi>π</mi><mo>,</mo><mi>π</mi><mi>π</mi><mi>π</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mi>K</mi><mi>K</mi><mi>π</mi></math> are calculated in the standard <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo><mo>×</mo><mi>U</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo></math> quark Nambu–Jona-Lasinio model. The intermediate channels with the states <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo><mi>π</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>500</mn><mo stretchy="false">)</mo><mi>η</mi></math> are taken into account in the decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mi>π</mi><mi>π</mi><mi>η</mi></math>. In the case of the scalar mesons, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>q</mi><mo stretchy="false">¯</mo></mover><mi>q</mi></math> representation as a chiral symmetric partners of the pseudoscalar mesons is used. It is shown that the decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mi>ρ</mi><mi>π</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mn>3</mn><mi>π</mi></math> occur due to the mass difference of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>u</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math> quarks. All the results are obtained without using any additional arbitrary parameters and are in satisfactory agreement with the known experimental data.</p>

JINR

M.K. Volkov

A.A. Pivovarov

K. Nurlan

Decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><msub><mrow><mi>f</mi></mrow><mrow><mn>1</mn></mrow></msub><mo stretchy="false">→</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>0</mn></mrow></msub><mi>π</mi><mo>,</mo><mi>π</mi><mi>π</mi><mi>π</mi></mrow><mo stretchy="false">(</mo><mi>η</mi><mo stretchy="false">)</mo></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>f</mi></mrow><mn>1</mn></msub><mo stretchy="false">→</mo><mi>K</mi><mi>K</mi><mi>π</mi></mrow></math> in the chiral <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>U</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo><mo>×</mo><mi>U</mi><mo stretchy="false">(</mo><mn>3</mn><mo stretchy="false">)</mo></mrow></math> quark NJL model