In this work, we investigate the equilibrium structure of white dwarfs within the covariant formulation of symmetric teleparallel <italic>f</italic>( <italic>Q</italic>) gravity, in which gravity is described by the nonmetricity scalar <italic>Q</italic> instead of spacetime curvature. We consider static and spherically symmetric stellar configurations composed of cold, fully degenerate electron matter and adopt a quadratic form of the gravitational Lagrangian, <math altimg='si7.svg'><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>Q</mi><mo linebreak='goodbreak'>+</mo><mi>&#945;</mi><msup><mi>Q</mi><mn>2</mn></msup></mrow></math>, where <italic>&#945;</italic> quantifies deviations from general relativity. The corresponding modified stellar structure equations are solved numerically in conjunction with the Chandrasekhar equation of state. We examine the impact of the parameter <italic>&#945;</italic> on the internal structure and global properties of white dwarfs, including the radial profiles of the metric potentials, pressure, density, nonmetricity scalar, and enclosed mass, as well as the mass&#8211;radius relation. While negative values of <italic>&#945;</italic> were explored, they lead to unstable or nonphysical configurations at high densities; therefore, the analysis is restricted to non-negative values of <italic>&#945;</italic>. Our results show that nonmetricity corrections produce significant deviations from the general relativistic predictions in the high-density regime. In particular, increasing <italic>&#945;</italic> modifies the equilibrium configurations and leads to a reduction in the maximum mass relative to the Chandrasekhar limit, accompanied by corresponding changes in the stellar radius and interior profiles. For <math altimg='si12.svg'><mrow><mi>&#945;</mi><mo linebreak='goodbreak'>=</mo><mn>5</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mn>18</mn></msup><mspace width='0.16em' /><mrow><msup><mtext>cm</mtext><mn>2</mn></msup></mrow></mrow></math>, we obtain a maximum mass <math altimg='si13.svg'><mrow><msub><mi>M</mi><mi>max</mi></msub><mo linebreak='goodbreak'>=</mo><mn>1.3519</mn><mspace width='0.16em' /><msub><mi>M</mi><mo>&#8857;</mo></msub></mrow></math> and radius <math altimg='si14.svg'><mrow><mi>R</mi><mo linebreak='goodbreak'>=</mo><mn>2228.85</mn><mspace width='0.16em' /><mtext>km</mtext></mrow></math>, which are consistent with the observational constraints of the ultra-massive white dwarf ZTF J1901+1458. These findings suggest that white dwarfs may serve as complementary astrophysical probes for testing the viability of <italic>f</italic>( <italic>Q</italic>) gravity in the strong-field regime.

India

Rajasmita Sahoo

White dwarf structure in <italic>f</italic>( <italic>Q</italic>) gravity

<p>Scalars carrying a conserved global charge <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Q</mi></math> can form stable localized field configurations composed of a large number of particles. These nontopological solitons are spherically symmetric and are called Q-balls. While usually analyzed in three spatial dimensions, these solitons can be straightforwardly generalized to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math> spatial dimensions. For <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>=</mo><mn>1</mn></math>, we can analytically solve the nonlinear differential equation for an important class of single-field potentials; for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>&gt;</mo><mn>1</mn></math>, we can analytically approximate the solutions in the thin-wall or large Q-ball regime, including the first subleading correction consistently. Since the underlying differential equations have the same form as vacuum-decay bounce solutions, our results find applications there, too.</p>

United States

Dusty Aiello

Julian Heeck

Q-balls across dimensions

We present a rigorous theoretical and observational analysis of the Hybrid <italic>f</italic>( <italic>Q</italic>) class of models by including the late-time modifying 1/ <italic>Q</italic> term. After deriving strict viability conditions from the analytical expansion history, we show that preserving early-universe structure formation dictates that the linear coupling be exactly unity. This fixes the background of the Hybrid model into a geometric degeneracy with &#923;CDM which is confirmed explicitly through MCMC analysis with the latest background-only probes. The physical novelty of this model is manifest in the perturbation sector, where the geometric coupling breaks the background degeneracy and induces a late-time suppression of the effective gravitational constant <italic>G<inf>eff</inf></italic>&#8239;&lt;&#8239; <italic>G<inf>N</inf></italic>. Consequently, the inclusion of RSD data reveals an amplitude compensation mechanism, by which the matching of the signature <italic>f&#963;</italic> <inf>8</inf> of the data causes the clustering amplitude <italic>&#963;</italic> <inf>8</inf> to inflate under weaker gravity. Statistical model comparison through AIC/DIC demonstrates that incorporating growth data yields a moderate to weak preference for the Hybrid model keeping the background cosmology intact. This provides a physically bounded alternative to &#923;CDM with a falsifiable signature in the large scale structure, directly testable by the next generation of galaxy surveys.

Ameya Kolhatkar

P.K. Sahoo

Beyond the cosmological constant: Breaking the geometric degeneracy of <italic>f</italic>( <italic>Q</italic>) cosmology via redshift-space distortions

We establish a new PBW basis for <math altimg='si1.svg'><msub><mi mathvariant='script'>A</mi><mi>q</mi></msub></math>, the alternating central extension of the <italic>q</italic>-Onsager algebra. Terwilliger showed that the alternating generators form a PBW basis in the block order <math altimg='si2.svg'><mrow><mi mathvariant='script'>G</mi><mo linebreak='goodbreak'>&lt;</mo><msup><mi mathvariant='script'>W</mi><mo>&#8722;</mo></msup><mo linebreak='goodbreak'>&lt;</mo><msup><mi mathvariant='script'>W</mi><mo>+</mo></msup><mo linebreak='goodbreak'>&lt;</mo><mover accent='true'><mrow><mi mathvariant='script'>G</mi></mrow><mo stretchy='true'>&#732;</mo></mover></mrow></math>. We prove that they also form a PBW basis in the different block order <math altimg='si3.svg'><mrow><msup><mi mathvariant='script'>W</mi><mo>&#8722;</mo></msup><mo linebreak='goodbreak'>&lt;</mo><mi mathvariant='script'>G</mi><mo linebreak='goodbreak'>&lt;</mo><mover accent='true'><mrow><mi mathvariant='script'>G</mi></mrow><mo stretchy='true'>&#732;</mo></mover><mo linebreak='goodbreak'>&lt;</mo><msup><mi mathvariant='script'>W</mi><mo>+</mo></msup></mrow></math>. Consequently, multiplication induces a vector-space isomorphism <display><formula id='ueq0001'><math altimg='si4.svg'><mrow><msup><mi mathvariant='script'>W</mi><mo>&#8722;</mo></msup><mi>&#8855;</mi><mi mathvariant='script'>G</mi><mi>&#8855;</mi><mover accent='true'><mrow><mi mathvariant='script'>G</mi></mrow><mo stretchy='true'>&#732;</mo></mover><mi>&#8855;</mi><msup><mi mathvariant='script'>W</mi><mo>+</mo></msup><mo>&#10230;</mo><msub><mi mathvariant='script'>A</mi><mi>q</mi></msub><mo>,</mo></mrow></math></formula></display>thereby confirming a conjecture of Terwilliger.

Singapore

Haoran Zhu

A new PBW basis for the alternating central extension of the <italic>q</italic>-Onsager algebra

The internal structure of the light scalar state $ a_0(1450) $ has not been definitively determined; it may comprise multiple possible configurations. Among these, it may be regarded as a $ q\bar{q} $ state. Based on this possibility, we use QCD light-cone sum rules to study the semileptonic decay process $ D \to a_0(1450)\ell \nu_\ell $ with $ \ell=(e, \mu) $ and to test this hypothesis. First, we construct two twist-2 light-cone distribution-amplitude schemes based on the light-cone harmonic-oscillator model, and present their moments $ \langle\xi^{n}\rangle |_{\mu} $ and Gegenbauer moments $ a_{n}(\mu) $ at $ \mu_0=1\; {\rm{GeV}} $ and $ \mu_k= 1.4\; {\rm{GeV}} $ for $ n=(1,3,5) $ . In the large-recoil region, we obtain the transition form factors (TFFs): $ f_+^{({\rm{S}}1)}(0) = $ $ 0.836_{-0.119}^{+0.116} $ , $ f_+^{({\rm{S}}2)}(0)=0.767_{-0.105}^{+0.106} $ , and $ f_-(0)=0.630_{-0.077}^{+0.078} $ . A simplified series expansion $ z(q^2, t) $ is used to extrapolate the TFFs to the entire physical $ q^2 $ region. For $ q^2=10^{-5} \; {\rm{GeV}}^2 $ , we compute the angular distribution of the differential decay width ${{\rm d}\Gamma}/{{\rm d}\cos\theta_\ell }$ over the range $ \cos\theta_\ell \in [-1,1] $ . Subsequently, we obtain the differential decay widths and branching fractions for $ D^0 \to a_0(1450)^- \ell^+ \nu_\ell $ and $ D^- \to a_0(1450)^0 \ell^- \bar{\nu}_\ell $ , with branching fractions of order $ 10^{-6} $ . Finally, we analyze three angular observables for the semileptonic decay process $ D^- \to a_0(1450)^0 \ell^- \bar{\nu}_\ell $ : the forward–backward asymmetry $ {\cal{A}}_{\rm{FB}} $ , the lepton polarization asymmetry $ {\cal{A}}_{\lambda_\ell} $ , and the $ q^2 $ -differential flat term $ {\cal{F}}_{\rm{H}} $ .

China

Ya-Lin Song

Yin-Long Yang

Ye Cao

Xue Zheng

Hai-Bing Fu

Searching the possibility of $\textit{a}$ $_{0}$(1450) scalar state being a q q state structure via charmed meson semileptonic decays * Supported in part by the National Natural Science Foundation of China (12265010), and the Guizhou Provincial Department of Science and Technology (MS[2025]219, CXTD[2025]030)

In this work, we investigate neutron stars (NSs) in the strong field regime within the framework of symmetric teleparallel $\textit{f}$($\textit{Q}$) gravity, considering three representative models: linear, logarithmic, and exponential. While Bayesian studies of NS observations are well established in general relativity and curvature based modified gravity theories, such analyses in $\textit{f}$($\textit{Q}$) gravity remain largely unexplored. For the first time we perform a Bayesian inference analysis by confronting theoretical NS mass-radius predictions with NICER observations of PSR J0030+0451, PSR J0740+6620, PSR J0437+4715, and PSR J0614+3329 in the background of nonmetricity based gravity. The dense matter equation of state is fixed to DDME2 in order to isolate the effects of modified gravity on NS structure. Our results indicate a statistical preference for the exponential $\textit{f}$($\textit{Q}$) model over the linear and logarithmic cases, as supported by the Bayes-factor analysis, and show that its parameters are comparatively well constrained. For this model, we obtain a radius and tidal deformability at $$1.4\,M_\odot $$ of $$R_{1.4} = 11.27^{+0.53}_{-0.36}\,\textrm{km}$$ and $$\varLambda _{1.4} = 156.95^{+84.02}_{-41.73}$$ , respectively, consistent with current observational constraints. The median values of the maximum mass are found to be around $$M_{\max }\approx 2.3M_\odot $$ for all three constrained models. However, the upper parts of the 95% credible regions of the mass-radius relations extend beyond $$2.5M_\odot $$ and approach $$\sim 3M_\odot $$ within the adopted framework. This indicates the possibility of comparatively massive stable compact configurations in the Bayesian constrained parameter space. These results highlight the potential of NSs as powerful probes of symmetric teleparallel gravity in the strong field regime. We note that these results are conditional on the use of a fixed DDME2 equation of state and the coincident-gauge formulation adopted in this work.

Sneha Pradhan

N. Patra

Kai Zhou

P. Sahoo

Bayesian inference of neutron star properties in $\textit{f}$($\textit{Q}$) gravity using NICER observations

While $\textit{CP}$ models with analytic potentials are known to support finite-energy compact Q-ball and Q-shell solutions, their behavior in more complex Lagrangian frameworks remains a subject of active research. This work explores these non-topological structures within an extended Skyrme-Faddeev-type model that incorporates quartic derivative terms. In this context, harmonic time dependence and the presence of quartic terms constitute two independent stabilization mechanisms that allow the configurations to circumvent Derrick’s scaling argument. We investigate the necessary conditions for the existence of these solutions and analyze the influence of quartic terms on the resulting compactons. Specifically, we examine the scaling relationship between energy and Noether charge, expressed as $\textit{E}$($\textit{Q}$) ~ |$\textit{Q}$| . Our numerical analysis demonstrates that $\textit{n}$ < 1, which supports the stability of these solutions against spontaneous fission.

Brazil

E. Colaço

P. Klimas

Poland

L. Livramento

Japan

N. Sawado

S. Yanai

Compact Q-balls and Q-shells within a $\textit{CP}$ $\textit{N}$ Skyrme-Faddeev type model

We employ the island formula to investigate the entanglement entropy of the Hawking radiation in an asymptotically AdS black hole background within the framework of <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> gravity. Through an analysis based on the Euclidean action, we find that the area term of the generalized entropy must be modified, which in turn leads to a modification of the island formula. Using the modified formula to compute the radiation entropy for an eternal asymptotically AdS black hole reveals that, the result diverges as the cutoff surface is moved outward, indicating the breakdown of the <italic>s</italic>-wave approximation. A possible reason is that we have neglected the gravitational back-reaction. For a collapsing asymptotically AdS black hole, the radiation entropy is dominated by the area term, with a correction proportional to the logarithm of the event horizon area, which is consistent with the predictions of quantum gravity. Both the radiation entropy and the Page time are ultimately influenced by the choice of the <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> model, implying that the information regarding the underlying gravitational model is encoded in the final radiation.

Yipeng Liu

Wei Xu

Baocheng Zhang

Radiation entropy in asymptotically AdS black holes within <math altimg='si1.svg'><mrow><mi>f</mi><mo>(</mo><mi mathvariant='double-struck'>Q</mi><mo>)</mo></mrow></math> gravity

We develop a unified framework for studying superposed coherent states in coupled nonlinear bosonic systems using a <italic>q</italic>-deformed Kerr oscillator model. A quantitative measure, termed catability, is introduced to quantify robustness and structural coherence of Schr&#246;dinger-cat-like states under nonlinear and deformation effects within the framework. Within the <italic>q</italic>-deformed bosonic algebra, we analyze the dynamics of two coupled Kerr oscillators to demonstrate that the deformation parameter governs coherence redistribution and nonlinear coupling-induced state transformation. Establish local cat states emerge from the relation between Kerr nonlinearity and <italic>q</italic>-deformed interactions, coherence transfer between subsystems becomes sensitive to the deformation strength. In this case, construct a phase diagram of catability, revealing distinct regimes of quantum behavior, identifying coupling-driven quantum phase transitions in a deformed algebraic structure system. The generalized analysis extended the covariant formulation and graphene-inspired catability operators generalized curved space-time backgrounds, establishing a connection between nonlinear quantum optics, condensed matter analog systems, relativistic quantum structures framework. In this context, results explain complete description deformation-controlled quantum coherence and establish new directions for engineered nonclassical states in complex quantum systems.

Algeria

Azerbaijan

Abdelmalek Bouzenada

q-deformed catability in coupled Kerr, graphene, and quantum phase transitions

We investigate the late-time dynamics of cosmic expansion within a torsion-free formulation of <italic>f</italic>( <italic>Q</italic>) gravity in a spatially flat Friedmann-Robertson-Walker universe. Adopting a specific non-metricity model that reduces to standard cosmology at early times, we explore whether accelerated expansion can emerge purely from geometric effects without introducing a cosmological constant. To probe the dynamical behavior of dark energy, three redshift-dependent parameterizations of the equation of state are considered. The resulting cosmological evolution is analyzed through a comprehensive set of diagnostics, including the effective equation of state, deceleration parameter, <italic>O</italic>m diagnostic and higher-order cosmographic quantities such as the jerk, lerk, and time parameter. These indicators consistently reveal a transition from decelerated to accelerated expansion and demonstrate clear deviations from the standard &#923;CDM scenario, highlighting the dynamical nature of the underlying models. Furthermore, the thermodynamical viability of the framework is examined by testing the generalized second law of thermodynamics, Gibbs free energy ( <italic>G</italic>) and heat capacity <italic>C</italic>. The positivity of the total entropy variation throughout the relevant redshift range confirms the thermodynamic consistency of the models. Moreover, the thermodynamical stability of the system is also confirmed by obtaining <italic>C</italic>&#8239;&gt;&#8239;0 and <italic>G</italic>&#8239;&lt;&#8239;0.

Nageen Pervaiz

Pakistan

Nadeem Azhar

Jin-Zeng Li

Kazakhstan

Abdul Jawad

Nurgissa Myrzakulov

Saken Toktarbay

Uzbekistan

Sanjar Shaymatov

Aray Muratkhan

Late-time cosmic acceleration in torsion-free <italic>f</italic>( <italic>Q</italic>) gravity: Dynamical and thermodynamical analysis