Wednesday, 4 November 2026: 8 new papers, 0 cross-lists and 1 replacement in General Physics (physics.gen-ph), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
We study scalar, Dirac, and electromagnetic test fields on a two-parameter family of static spacetimes, labeled by an angular winding number $k$ and an anisotropy parameter $\alpha$ that shortens one direction of the transverse metric relative to the other. Only the members with $k=1$ and $\alpha<1$ are conical, as for an ordinary straight cosmic string. The remaining members are nonconical and, except in the flat cases, curved and nonvacuum. A common spin-weighted connection Laplacian organizes the local equations, while the curvature coupling, global field conditions, and constraints are fixed separately for each physical field. Explicit frame transitions remove spurious winding dependence in the flat limit. For the nonconical members of the family, isothermal coordinates yield an exact factorization of the indicial equation and determine its monodromy: the indicial exponents are independent of the anisotropy parameter, although the finite-domain eigenvalues are not. We derive variational bounds and a weak-anisotropy selection rule for the scalar spectrum. The electromagnetic equations are obtained from the four-potential in Lorenz gauge, with gauge-invariant transverse-electric (TE) and transverse-magnetic (TM) reductions and an annular transverse-electromagnetic (TEM) mode. Finite-element computations on an annulus, validated against benchmarks, are consistent with the bounds, confirm the selection rule, give MIT bag Dirac and conducting-wall Maxwell spectra, and reproduce the invariance of the transverse-electromagnetic capacity under $k\mapsto2-k$, an exact consequence of a radial inversion of the Dirichlet energy.
We investigate the late-time expansion history of the Universe within the framework of $f(Q, C)$ gravity by adopting a linear parametrization of the deceleration parameter $q(z) = \alpha+\beta H$, where $Q$ denotes the non-metricity scalar and $C$ represents the associated boundary term satisfying the geometrical relation $\mathring{R}= Q+C$. The adopted parametrization provides a phenomenological description of the cosmic expansion while retaining analytical tractability, allowing the transition from decelerated to accelerated expansion to be examined directly. An exact integration of the corresponding differential equation yields the closed-form Hubble function, $H(z)=\frac{1}{\beta\left[F_0-\ln(1+z)\right]},$ thereby providing an explicit description of the expansion history in terms of redshift. Here $F=\frac{1}{\beta}\sqrt{2\beta t+b}$ and $F_0$ specifies the value of $F$ at the present epoch. The model parameters are constrained using recent Cosmic Chronometer (CC) measurements, DESI DR2 Baryon Acoustic Oscillation (BAO) observations, Pantheon+SH0ES Type Ia supernovae, and the Union3 observations through Bayesian Markov Chain Monte Carlo (MCMC) analysis. Individual and combined datasets are compared to assess the model's consistency, while its cosmic evolution is examined using the deceleration, the equation-of-state parameter, the state-finder pair ${r,s}$, and the $Om$ diagnostic.
Power density is a central measure underlying a common thread in cosmic evolution. It measures the rate at which free energy transits in a complex system of a given mass. We argue that it can be seen as a universal signature, and thus a strategy of ''following high power density'' can inform both biosignature and technosignature searches. We use known binary star masses and accretion rates to compute power densities of cataclysmic variables, neutron stars and transient black holes, and show that these accreting binaries have high power densities. We compare this result with other accreting systems in astrophysics as controls: young stellar objects (YSOs) and supermassive black holes (SMBHs). We review possible natural explanations, and then explore the possibility that these accreting binary systems might be instances of Type II stellar civilizations on Kardashev's scale, civilizations feeding on stars, or $\textit{stellivores}$. Besides power density, we present additional living clues, such as their variety, their existence far from thermodynamic equilibrium, their apparent homeostasis, the need to fine-tune models to explain them, the apparent existence of energy reserves, accretion control and ejection control, as well as other potential living systems functions. We summarize this case using living systems theory and discuss implications for big history.
The Barrow correction to the horizon entropy changes the total number of microstates associated with the horizon, whereas the Kaniadakis correction provides an alternate statistical description of these microstates different from Boltzmann-Gibbs statistics. In this paper, we consider the Kaniadakis description of the Barrow-corrected horizon entropy analogous to its description of the standard horizon entropy. The modified Friedmann equations were derived for an $(n+1)$-dimensional non-flat universe through two different approaches --- the law of emergence and the first law of thermodynamics. The generalised second law of thermodynamics was investigated, and the density contrast evolution equation was also derived. We take the universe to be composed of only matter and constrain the model parameters through an MCMC analysis using observational Hubble data, Pantheon+ Type Ia supernovae data, baryon acoustic oscillation distances from the DESI DR2 data release, and $f\sigma_{8}$ measurements from redshift-space distortions. The Kaniadakis parameter $K$ was constrained away from zero, showing a preference for the $K$-deformed statistical approach. Motivated by recent studies, we considered a wider parameter space for the Barrow index, $\Delta \in (-1,1]$. In agreement with observational data, we obtained $\Delta = -0.335\pm0.031$, motivating a horizon structure different from Barrow's sphereflake configuration. The present value of the Hubble parameter was constrained as $H_{0}=(66.98 \pm 0.71)$ km/s/Mpc, which leans towards the early-universe Planck estimates; however, late-time data alone are insufficient to study the Hubble tension problem. Analysing the evolution of various cosmological parameters, we conclude that the modified Friedmann dynamics of the model produces a viable expansion history and late-time acceleration without invoking a dark energy component.
In this paper, we investigate the classical properties of a non-linear electrodynamics that emerges from one loop effective action for fermions coupled to an antisymmetric background tensor, that breaks the Lorentz symmetry in the model. The conservation laws are obtained through the Belinfante-Rosenfeld energy-momentum tensor in the non-linear electrodynamics that provides the energy density, the Poynting vector, the linear momentum and the stress tensor. In particular, this Lorentz symmetry violation breaks the symmetric index of the energy-momentum tensor, but it preserves the gauge invariance, as we expect. We introduce the prescription of a magnetic background field, that we consider constant and uniform. For propagation effects, the model is linearized by the magnetic background. This prescription allows us investigations of the plane wave propagation in the presence of an external magnetic field. In this context, we obtain the constitutive relations of the material medium, that behaves like an bi-anisotropic medium. Thereby, we calculate the refractive index whose one of the solutions show the total absorption of the wave in the medium. Using the wave equation for linear polarization, we investigate the birefringence phenomenon when the linear wave polarization changes with the magnetic background direction. The birefringence is so related to one of the spatial component of the LSV tensor in which we estimate through the PVLS experiment. We use one of the dispersion relations to obtain the kinematic of the Compton effect in the presence of the LSV parameter.
We study a cosmological scenario in which the Universe contains standard baryonic matter, radiation, and a single unified dark fluid, the umami Chaplygin gas, which accounts for both dark matter and dark energy with no separate dark-matter component. We first analyse the thermodynamic behaviour of the fluid and show that, unlike earlier Chaplygin-type models, its thermodynamic stability is conditional rather than global: stability holds only above a critical density $\rho_1=\sqrt{|A/w|}$, the fluid reheats once this density is crossed, and a viable low-density regime requires $|w|<2$. Thermodynamic stability at the present epoch requires $|A|<|w|\rho_0^2$, a condition that is more easily met for $|w|>1$. We then constrain both the $|w|<1$ and $|w|>1$ cases with Type Ia supernovae, DESI DR2 baryon acoustic oscillations, cosmic-chronometer Hubble data and Planck 2018 distance priors through a Markov Chain Monte Carlo analysis. The $|w|<1$ case fits all four datasets well, with $w \simeq -0.73$, $\Omega_m^{\rm eff} \simeq 0.32$ and $H_0 \simeq 66.8$ km s$^{-1}$ Mpc$^{-1}$. It is statistically comparable to flat $\Lambda$CDM, with $\Delta{\rm AIC}=-4.8$ and $\Delta{\rm BIC}=+0.6$. Its best-fit parameters violate the stability condition. The $|w|>1$ case with a Gaussian prior satisfies the condition but fits worse, with $\Delta{\rm AIC}\simeq+66$ relative to $\Lambda$CDM. The best fit that obeys the condition exactly still has $\Delta{\rm AIC}\simeq+50$. Finally, a linear perturbation analysis shows that the adiabatic sound speed turns negative at exactly the same critical density, triggering exponential small-scale growth at late times in the observationally preferred case. These results reveal a tension between a good fit to background data and the physical stability of the umami unified dark fluid.
Understanding the physical origin of the Universe's late-time accelerated expansion remains one of the central open problems in modern cosmology. Geometrothermodynamics (GTD) offers a compelling route to this problem, providing a geometric framework that unifies thermodynamics with contact and Riemannian geometry to encode the equilibrium properties of a physical system directly into its underlying geometric structure. In this work, we employ the GTD formalism to investigate cosmological models capable of explaining the observed accelerated expansion of the Universe. As an important outcome, our simple model exhibits dynamical behavior that provides a reasonable description of the late-time evolution of the Universe. We study the Chaplygin-Jacobi and Chaplygin-Abel gas models and their variable forms within geometrothermodynamics by deriving their thermodynamic relations, entropy, and equations of state. The free parameters of the models are constrained through a Markov Chain Monte Carlo (MCMC) analysis using several observational datasets, including cosmic chronometers combined with baryon acoustic oscillations (CC+BAO), DESI DR2 BAO data, DESI DR2 combined with the DES-SN5YR and Union3 Type Ia supernova compilations. The statistical performance of the models is assessed using the Akaike and Bayesian Information Criteria (AIC and BIC). We further examine their cosmological evolution through the deceleration parameter, the dark-energy equation-of-state parameter, and higher-order kinematic diagnostics, including the jerk and snap parameters. The perturbative stability of the models is also investigated through the squared sound speed.
We investigate a semi-empirical flavour framework based on two linked hypotheses: a golden/pentagonal organisation of fermion mixing and the recurrence of its hierarchy maps in the quark-mass spectrum. The two large lepton angles are specified by the fifth-order Chebyshev conditions $T_5(\theta_{12}^{\ell})=0$ and $T_5(\theta_{23}^{\ell})=-1$, with angular arguments in radian measure, while the smaller reactor angle follows the approximate bilinear relation $\theta_{13}^{\ell}\simeq\theta_{12}^{\ell}\theta_{23}^{\ell}/\pi$. An alternative golden-partition construction yields nearly identical large-angle predictions and an exact circular--hyperbolic duality. The golden ratio $\varphi$ also enters two distinct geometrical prescriptions for the Cabibbo angle, while the heptadecagonal seed $\alpha_C=\pi/17$ governs the suppressed mixing hierarchy. The near-equality $\tan\alpha_C\simeq\cos54^\circ/\pi$ further connects the two geometries. The resulting quark hierarchy obeys the quadratic map $\theta_{13}^q=\sqrt{\theta_C^2+(\theta_{23}^q)^2}-\theta_C\simeq(\theta_{23}^q)^2/(2\theta_C)$. Transferring the quadratic and bilinear maps to quark masses yields the crossed relations $m_d\simeq m_c^2/(2m_t)$ and $m_u\simeq m_b m_s/(m_F/\varphi)$, where $m_F=G_F^{-1/2}$. The complementary triples $(t,c,d)$ and $(b,s,u)$ reproduce both mass targets within $1\%$ for the adopted reference values. Gatto--Sartori--Tonin-type correspondences and Froggatt--Nielsen scaling provide compatible phenomenological interpretations. These results suggest a common golden/geometrical organising structure for flavour mixing and mass hierarchies, whose underlying dynamical origin remains to be established.