We investigate the cosmological dynamics of Parameterized Absolute Parallelism (PAP) geometry within the framework of modified $$f(R,\Sigma ,T)$$ gravity. By generalizing the Gauss–Bonnet invariant $${\mathcal {G}}_b$$ using the PAP curvature tensor $$B^{\alpha }{}_{\mu \nu \sigma },$$ we incorporate both Riemannian curvature and torsion effects into a unified framework. The modified field equations are derived for a spatially flat FLRW background, and exact analytical solutions for the Hubble parameter, scale factor, energy density, and pressure are obtained under a constant equation-of-state parameter $$\omega .$$ Our analysis shows that the PAP deformation parameter $\textit{b}$ and matter–torsion coupling $$\eta $$ significantly modify cosmic expansion, the effective equation of state, and curvature diagnostics. Furthermore, we explore the role of $${\mathcal {G}}_b$$ in torsion-driven Gauss–Bonnet inflation and demonstrate how PAP corrections alter the slow-roll dynamics, enabling sustained inflation even for flat potentials. A detailed stability analysis reveals the critical regions in the $$(b,\eta )$$ parameter space separating stable and unstable cosmological phases. This unified approach recovers General Relativity, teleparallel gravity, and minimally coupled PAP models as limiting cases, offering new insights into early- and late-time acceleration driven by torsion and higher-curvature effects.

Egypt

Tahia Dabash

Saudi Arabia

A. Eid

M. Bakry

Gauss–Bonnet effects in $$f(R,\Sigma ,T)$$ gravity

<p>Light bosonic dark matter fields that can be treated like a classical wave have nonlinear field values close to massive bodies. Here we make the important observation that the quadratic interactions of axion dark matter lead to nonperturbative axion field values for values of the decay constant of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>f</mi><mo>≲</mo><msup><mn>10</mn><mn>13</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and masses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>≲</mo><mn>7</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup><mo>/</mo><mi>f</mi><mtext> </mtext><mtext> </mtext><msup><mrow><mi>eV</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> and generalize this result for axionlike particles. We identify experimental observables impacted by this effect.</p>

United Kingdom

Martin Bauer

Sreemanti Chakraborti

Validity of bounds on light axions for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>f</mi><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>13</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>

Antikaon ( <math altimg='si2.svg'><msup><mi>K</mi><mo>&#8722;</mo></msup></math>) condensation within neutron star matter (NS) depends on the antikaon-nucleon interaction potential ( <italic>U<inf>K</inf></italic>). Its onset softens the equation of state (EOS), and the resulting changes in stellar structure may serve as indicators of the phase transition from nucleonic matter to <math altimg='si2.svg'><msup><mi>K</mi><mo>&#8722;</mo></msup></math> condensed matter. We investigate the impact of <math altimg='si2.svg'><msup><mi>K</mi><mo>&#8722;</mo></msup></math> condensation on NS properties using Bayesian inference with two RMF parameter sets: the stiff DD2 and the softer FSU EOS. Multimessenger observations from NICER and LIGO/Virgo constrain <math altimg='si12.svg'><mrow><msub><mi>U</mi><mi>K</mi></msub><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mn>104</mn><mo>.</mo><msubsup><mn>72</mn><mrow><mo>&#8722;</mo><mn>12.48</mn></mrow><mrow><mo>+</mo><mn>13.82</mn></mrow></msubsup></mrow></math> MeV (DD2) and <math altimg='si13.svg'><mrow><msub><mi>U</mi><mi>K</mi></msub><mo linebreak='goodbreak'>=</mo><mo>&#8722;</mo><mn>66</mn><mo>.</mo><msubsup><mn>46</mn><mrow><mo>&#8722;</mo><mn>3.42</mn></mrow><mrow><mo>+</mo><mn>2.47</mn></mrow></msubsup></mrow></math> MeV (FSU) respectively. Deeper <math altimg='si2.svg'><msup><mi>K</mi><mo>&#8722;</mo></msup></math> potentials trigger condensation at a lower density, softening the EOS and lowering the corresponding maximum masses. While slopes of mass-radius and tidal deformability curves overlap between nucleonic and exotic EOSs, their curvature and <math altimg='si6.svg'><mrow><mi>f</mi><mo linebreak='goodbreak'>&#8722;</mo></mrow></math>mode oscillation properties (frequency and damping time) reveal features attributable to EOS softening. However, distinguishing the specific exotic degrees of freedom responsible for the softening remains an open challenge.

India

Debanjan Guha Roy

Sarmistha Banik

Signatures of <math altimg='si2.svg'><msup><mi>K</mi><mo>&#8722;</mo></msup></math> condensation on neutron star structure and <math altimg='si6.svg'><mrow><mi>f</mi><mo linebreak='goodbreak'>&#8722;</mo></mrow></math>mode frequencies

Motivated by the first observation of $\rm CP $ violation in baryon decays, we study the topological amplitudes of bottom baryon decays in the $ S U(3)_{\rm F} $ limit. The topological diagrams of the charmless two-body decays of bottom baryons are presented in detail. The linear relations between topologies and $ S U(3) $ irreducible amplitudes are derived through tensor contraction and $ S U(3) $ decomposition. Four amplitudes among the 13 independent amplitudes are critical to the $\rm CP$ asymmetries. The small $ \rm CP $ asymmetries might indicate small relative strong phases between amplitudes $ A_2 $ and $ A_{12,14}^\prime $ . To avoid them, we suggest measuring $\rm CP $ asymmetries in the $ \Xi^0_b\to pK^- $ and $ \Xi^-_b\to \Lambda^0 K^- $ decays. Furthermore, the Körner-Pati-Woo theorem can be tested by measuring the branching fractions of the $ \Lambda_b^0\to\Sigma^0K^0_S $ and $ \Lambda_b^0\to\Sigma^-K^+ $ modes.

China

Di Wang

Wei-Chen Fu

Topological amplitudes of bottom baryon decays in the $\textit{SU}$(3)$_{F}$ limit * Supported in part by the National Natural Science Foundation of China (12105099)

We use a modified relativistic quark model to study the properties of excited charmed and charmed strange mesons. We calculate the masses and wave functions of conventional charmed and charmed strange mesons incorporating both spin and $\textit{S}$-$\textit{D}$ mixing effects and fit parameters of the potential model with known experimental states using differential evolution techniques. Using leading Born-Oppenheimer expansion, we compute the spectrum and wave functions of the first gluonic excited state of charmed and charmed strange mesons. We examine the effects of gluonic excitation on the spectrum of the resulting hybrid mesons. Using our calculated spectrum and wave functions, we determine the radiative transitions of the conventional and hybrid open charm mesons. We compare our calculations with experimental data and other works. We expect our results will be beneficial in the detection of charmed and charmed strange conventional and hybrid mesons.

Pakistan

Saba Noor

Faisal Akram

Bilal Masud

Study of excited $\textit{D}$ and D$_{s}$ mesons in a relativized quark model * F. A. acknowledges HEC grant 20-15728/NRPU/R&D/HEC/2021, Pakistan

The classical Isaacson’s procedure for describing back-reaction of the averaged energy–momentum for high frequency gravitational waves is generalized to the $\textit{f}$($\textit{R}$) gravity case. From the beginning it is assumed that an initial background could be arbitrary one. Then, we restrict the background to be de Sitter, which is a novelty regarding the study of a back-reaction in $\textit{f}$($\textit{R}$) gravity. Consideration of the de Sitter space as a background spacetime allows us to provide the averaging procedure completely. Using the results on the de Sitter space and generalizing the Isaacson procedure, we construct the averaged energy–momentum on an additionally curved (averaged) background. Consistency tests for de Sitter spacetime are performed both at the background and perturbative regimes. Our results generalize previous studies in which the authors consider the flat (Minkowski) spacetime as the initial background.

Russia

Petr Tretyakov

Alexander Petrov

On energy–momentum tensor for gravitational waves in $\textit{f}$($\textit{R}$) gravity

<p>This study investigates the mass spectra and decay behaviors of the experimentally unobserved <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1</mn><mi>F</mi></math>-wave singly bottom baryons. Calculating their mass spectra could provide crucial guidance for determining their spectroscopic positions. Additionally, by analyzing their decay properties, we could predict the important decay channels, which are essential for experimental searches and quantum number assignments. Our calculations aim to support ongoing experimental and theoretical efforts in singly bottom baryon spectroscopy.</p>

Zi-Le Zhang

Si-Qiang Luo

Spectroscopic properties of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1</mn><mi>F</mi></math>-wave singly bottom baryons

This study is concern to the homothetic symmetry approach to get exact solutions for locally rotationally symmetric (LRS) Bianchi type-I spacetimes within the framework of <math altimg='si108.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></math> gravity, revealing that such spacetimes posses homothetic symmetry of different dimensions. By employing the Rif tree algorithm implemented in Maple, we systematically transform the symmetry and field equations into a set of constraints on the metric functions, enabling the derivation of exact analytical forms for the homothetic vector fields. Furthermore, we compute the corresponding physical quantities, including the energy density <math altimg='si109.svg'><mi>&#961;</mi></math>, pressure <math altimg='si110.svg'><mi>p</mi></math>, Ricci scalar <math altimg='si111.svg'><mi>R</mi></math>, shear scalar <math altimg='si8.svg'><msup><mi>&#963;</mi><mn>2</mn></msup></math>, equation of state <math altimg='si112.svg'><mi>w</mi></math> and modified gravity function <math altimg='si113.svg'><mrow><mi>F</mi><mo>(</mo><mi>r</mi><mo>)</mo></mrow></math>, for each solution, providing crucial insights into the geometric and physical properties of these spacetimes within the <math altimg='si107.svg'><mrow><mi>F</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></math> gravity.

Jamshed Khan

Sumaira Saleem Akhtar

Ambreen Ayub

Exact LRS Bianchi type I solutions in quadratic <math altimg='si107.svg'><mrow><mi>F</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></math> gravity from homothetic symmetries: A Rif tree approach

We investigate the construction and viability of rotating Casimir wormholes within the framework of $\textit{f}$($\textit{R}$) gravity, focusing on models of the form $$f(R) = R + \alpha R^2$$ . Building upon previous work in general relativity, where the Casimir effect serves as a physically motivated source of exotic matter, we explore how higher-order curvature corrections impact the energy conditions, stability, and traversability of rotating wormhole geometries. Using a perturbative expansion around small curvature deviations, we derive the modified field equations for a stationary, axisymmetric metric and analyze the interplay between the Casimir-induced stress-energy tensor, thermal corrections, and the effective geometric contributions from $\textit{f}$($\textit{R}$) gravity. Our results show that the inclusion of curvature-induced terms can significantly reduce, and in some parameter regimes locally mitigate, the null energy condition (NEC) violation near the throat. We identify angular velocity profiles, particularly those with exponential damping, that are compatible with the modified gravitational dynamics and helping stabilize the wormhole configuration. A detailed linear perturbation analysis reveals that scalar modes associated with $\textit{f}$($\textit{R}$) gravity can enhance the stability of the wormhole under fluctuations. Furthermore, we evaluate the behavior of the weak, strong, and dominant energy conditions and assess tidal forces experienced by travelers, confirming that these wormholes can be traversable under physically reasonable conditions. This study highlights the potential of modified gravity to support stable, traversable wormhole solutions with reduced reliance on exotic matter.

Iran

Behnam Pourhassan

Rotating Casimir wormholes in $\textit{f}$($\textit{R}$) gravity: a modified gravity extension of exotic spacetime models

In this work, we study early-time inflation within a class of <math altimg='si9.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi>&#981;</mi><mo>,</mo><mi>X</mi><mo>)</mo></mrow></math> gravity models under a constant-roll condition. Employing a generalized potential of the form <math altimg='si10.svg'><mrow><mi>V</mi><msup><mrow><mo>(</mo><mi>&#981;</mi><mo>)</mo></mrow><mi>&#963;</mi></msup></mrow></math>, we derive expressions for the spectral index <math altimg='si1.svg'><msub><mi>n</mi><mi>s</mi></msub></math> and tensor-to-scalar ratio <math altimg='si11.svg'><mi>r</mi></math>, demonstrating that the inflationary dynamics are primarily governed by the parameter <math altimg='si6.svg'><mi>&#963;</mi></math> and the shape of the potential. At the upper limit of <math altimg='si1.svg'><msub><mi>n</mi><mi>s</mi></msub></math>, we obtain a de Sitter-like phase, while at the lower limit, the model transitions to a quintessence-like phase through an effective oscillating equation of state parameter (EoS). Therefore, under the tuning parameter <math altimg='si12.svg'><mrow><mi>&#963;</mi><mo linebreak='goodbreak'>&lt;</mo><mn>1</mn></mrow></math>, the model exhibits a smooth transition from a de Sitter-like phase to a quintessence-like phase via the oscillating EoS parameter. The resulting predictions are consistent with recent observations from the Atacama Cosmology Telescope (ACT), combined with CMB lensing and DESI BAO data.

Türkiye

A.I. Keskin

Mehmet Yaşar

K. Kurt

Constant roll inflationary dynamics with generalized potentials in <math altimg='si9.svg'><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><mi>&#981;</mi><mo>,</mo><mi>X</mi><mo>)</mo></mrow></math> gravity