Papers

We study nonrotating neutron stars in energy–momentum squared gravity (EMSG). The stellar models are obtained from the modified Tolman–Oppenheimer–Volkoff equations and four original tabulated hadronic equations of state: WFF1, SLy4, APR4, and MPA1. We use the common coupling set $\alpha\in\{-20,-10,0,+5,+7.5\}\,\mathrm{km}^{2}$ and construct mass–radius and mass–central-density sequences. We compare these sequences with the $2\,M_\odot$ mass requirement, the NICER measurements of PSR J0030+0451 and PSR J0740+6620, and the region inferred from GW170817. Within the sampled coupling range, the computed pre-turning-point branches remain compatible with these four benchmarks. Negative values of $\alpha$ generally shift the high-density branches toward larger masses. Positive values produce smaller shifts in the opposite direction. The microscopic sound speed becomes superluminal at high density in the WFF1 and SLy4 tables, whereas APR4 and MPA1 remain causal over their tabulated ranges. For WFF1, the causal boundary falls within a coarse table segment. Its compatibility with the $2\,M_\odot$ requirement therefore cannot be decided at the available density resolution. At $\alpha=-20\,\mathrm{km}^{2}$, the effective-fluid sound-speed diagnostic becomes singular for WFF1, SLy4, and APR4. This singularity is absent from the explicit modified TOV system. All computed sequences remain below the standard Buchdahl reference values for compactness and surface redshift.

We systematically investigate four cosmological models within a parameterized framework that allows for a redshift dependence of \(H_0\): three phenomenological models (\(\alpha\Lambda\)CDM, \(\alpha w\)CDM, and \(\alpha w_0w_a\)CDM), and the $J$CDM model motivated by big bang quantum cosmology. Using cosmic microwave background (CMB) data, baryon acoustic oscillations (BAO), cosmic chronometer (CC) measurements of the Hubble parameter, and three Type Ia supernova samples (PantheonPlus, DESY5, and Union3), we perform Markov chain Monte Carlo (MCMC) analyses to obtain posterior distributions of the model parameters. We also perform separate analyses using early-time and late-time data to assess how each observational epoch affects the model constraints. For the three phenomenological models, the parameter \(\alpha\) describing the redshift evolution of \(H_0\) is consistent with zero within \(2\sigma\). The Hubble constant inferred from the \(\alpha\Lambda\)CDM model is consistent with CMB results, while the $J$CDM model yields a larger Hubble constant but is strongly disfavored by model comparison criteria. Using the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC) for model comparison, we find that the standard \(\Lambda\)CDM model remains the most favored by the data. Among the four models, the \(\alpha w_0w_a\)CDM model shows a marginal AIC advantage ($\rm \Delta AIC \sim$ -2 to -13). However, this preference does not translate into a reduction of the Hubble tension, which is consistent with existing studies supporting dynamical dark energy. Moreover, none of the models can simultaneously satisfy both the early- and late-time constraints, and the combined datasets alone are insufficient to conclusively determine whether these parametrizations can resolve the tension.

Despite the remarkable observational success of the $\Lambda$CDM model, the physical origin of dark energy and the cosmological constant remain unresolved, motivating the exploration of dynamical vacuum scenarios within modified theories of gravity. Inspired by the quantum field theoretical description of running vacuum energy, we investigate a running vacuum cosmology in the framework of linear $f(R,T)=R+\lambda T$ gravity. Unlike recent studies that establish an effective correspondence between running vacuum energy and modified gravity, our approach directly incorporates a quantum field theory motivated running vacuum scenario into the $f(R,T)$ framework and examines its cosmological implications. Exact analytical solutions of the modified field equations are obtained in a spatially flat Friedmann–Lemaître–Robertson–Walker spacetime, yielding an analytical expression for the Hubble parameter. The free model parameters are constrained using the latest Pantheon+SH0ES compilation, DESI baryon acoustic oscillation measurements, and their joint dataset through Markov Chain Monte Carlo analysis. The observationally constrained model successfully reproduces the observed expansion history, remains consistent with independent Cosmic Chronometer measurements, predicts an age of the universe within current observational bounds, and yields an effective equation of state compatible with current observations. Furthermore, the statefinder and $Om$ diagnostics indicate close agreement with the $\Lambda$CDM scenario at late times, while the generalized second law of thermodynamics remains valid throughout cosmic evolution. These results demonstrate that the proposed framework provides an observationally viable and thermodynamically consistent realization of running vacuum cosmology in $f(R,T)$ gravity, offering a theoretically motivated alternative for describing the present accelerated universe.

In this work, we investigate the modified emergent dark energy (MEDE) model using baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), together with CMB information from the LoLLiPoP (low-$\ell$) and HiLLiPoP (high-$\ell$) likelihoods based on the latest Planck NPIPE PR4 release, Planck PR4 lensing, ACT DR6 lensing, and three Type Ia supernova samples (Pantheon$+$, DES-Dovekie, and Union3). We find that the MEDE model remains largely consistent with the standard $\Lambda$CDM cosmology. Although small departures from $\Lambda$CDM are allowed, the inclusion of SNe~Ia data drives the model parameters toward the standard cosmological scenario, with the parameter $\alpha$ remaining consistent with $\alpha=0$ at the $1\sigma$ level. The model does not significantly alleviate the $H_0$ or $S_8$ tensions: the inferred $H_0$ values remain below the SH0ES measurement, the sound horizon $r_d$ is nearly unchanged, and the predicted $S_8$ values remain close to those of $\Lambda$CDM. The reconstructed cosmological evolution closely follows the $\Lambda$CDM prediction, with deviations generally below the $0.5\sigma$ level. While the CMB + DESI DR2 dataset favors a full phantom regime, the inclusion of SNe~Ia shifts the evolution toward a full quintessence regime. Finally, although the $\Delta\chi^2_{\rm MAP}$ and $\Delta{\rm AIC}$ criteria indicate a marginally better fit than $\Lambda$CDM, the logarithmic Bayes factor provides only inconclusive evidence in favor of the MEDE model. Overall, the MEDE model remains compatible with current observations but does not exhibit the phantom-crossing behavior suggested by recent DESI DR2 analyses.

We construct an information theory framework in which the fundamental objects are binary sequences of length $n$, equipped with the bitwise XOR operation. The only physical observables are counts of XOR-generated symbol classes, while the exact locations of symbols are inaccessible. Averaging over those locations ultimately yields the Minkowski interval as an invariant object that maximizes (information) entropy. Correlations between two binary sequences are base-4 sequences that we label as “events”, and events are connected with maps. The entire kinematic structure of Special Relativity is recovered under minimal assumptions, i.e. counts that represent space and time increments carry equal informational weight. The central claim is that Lorentz symmetry is the typical large-n behaviour of XOR counting. At finite $n$ the framework yields a discrete rapidity spectrum, a bound $\gamma_{\max} = O(\sqrt{n})$, and interval fluctuations of relative size $O(n^{-1/2})$, with standard special relativity recovered as $n \to \infty$. However, the light cone and one null coordinate are exact for every microscopic configuration, so the symmetry group is undeformed and dispersion relations are unmodified. Thus, the theory, though discrete, implies no Lorentz violation of the standard phenomenological kind. Ultra-high-energy cosmic rays already require $n \gtrsim 10^{23}$; interferometry excludes the variant in which $n$ scales linearly with system size, leaving a holographic area law. The most striking prediction of the framework concerns systems at the maximum of their information capacity, where $n$ is necessarily finite: black holes and de Sitter space. There the corrections are of order one within a Planck proper length of the horizon, regardless of the horizon's size, and the spacetime description fails altogether at the endpoint of black-hole evaporation, where $n$ itself is of order unity.

We investigate the cosmological viability of Barrow holographic dark energy in a spatially flat Friedmann–Lemaître–Robertson–Walker universe in which the dark matter component is allowed to have a non-zero pressure, characterized by a constant equation-of-state parameter $w_{m}$. By considering the future event horizon as the infrared cutoff, we derive the master equation, which describes the cosmological dynamics for the background space. We constrain the model against late-time data, combining the baryon acoustic oscillation from DESI DR2 with three different catalogues for the Type Ia Supernova measurements and the Cosmic Chronometers. The dark matter equation of state is constrained to $w_{m}=0.033_{-0.030}^{+0.045}$, $0.009_{-0.041}^{+0.047}$, and $0.033_{-0.029}^{+0.042}$, for the PantheonPlus, the Union3.0 and the DES-Dovekie supernova datasets respectively. Therefore, the pressureless limit is recovered within the $2\sigma$ regime. On the other hand, the Barrow exponent is weakly constrained, due to the $\Delta-w_{m}$ degeneracy. The dark energy equation of state remains above the phantom divide throughout the redshift range probed. Finally, in the comparison of the statistical parameters with that of $\Lambda$CDM, it follows $\Delta\mathrm{AIC}=+2.23$, $+0.75$, and $+1.38$, $\ $while for the Bayesian evidence we find $\Delta\ln Z=-0.63$, $+0.47$, and $-0.13$, which suggest that the datasets considered in this analysis do not have a preferred model. Finally the relation with the corresponding Tsalis holographic dark energy model is discussed.

This work examines the physical characteristics of charged, anisotropic compact spheres within the framework of $f(R,\phi,X)$ modified gravity. Starting from a static, spherically symmetric spacetime, we employ an Adler-type ansatz for the temporal metric component $g_{tt}$. The corresponding radial metric component $g_{rr}$ is then systematically derived through application of the Karmarkar condition, which ensures a class-one embedding for the interior geometry. A crucial aspect of our approach involves matching the interior solution at the stellar boundary to the exterior Reissner–Nordstr$\ddot{0}$m spacetime—the established vacuum solution for charged, non-rotating masses. This matching procedure is essential for determining integration constants and verifying global physical consistency. Our comprehensive analysis of the resulting stellar model investigates multiple physical aspects, including energy density, radial and tangential pressures, anisotropy, equation-of-state parameters, energy conditions, mass function, compactness, and surface redshift. Stability assessment further incorporates examination of the adiabatic index and the Tolman–Oppenheimer–Volkoff equation. Collectively, our findings demonstrate that the charged compact star model presented here constitutes a physically viable configuration—free of singularities and maintaining stable equilibrium across the considered parameter space.

We investigate late-time Barrow holographic dark energy (BHDE) with Ricci cutoff in $f(Q,L_m)=Q+\alpha Q^n-2L_m$ gravity. The $Q^n$ term modifies the symmetric-teleparallel geometry, while $\Delta$ deforms holographic energy via entropy-area relation. Linear matter Lagrangian allows separate identification of geometric and holographic effects. Modified Friedmann equations with Ricci-cutoff BHDE yield a closed first-order equation for $E(z)=H(z)/H_0$, solved numerically. The model evolves from matter domination to late-time acceleration. Increasing $n$ makes $w_{\mathrm{DE},0}$ less negative, raises $z_t$, lowers $j_0$; increasing $\Delta$ makes $w_{\mathrm{DE},0}$ and $q_0$ more negative, raises $z_t$ and $j_0$. Calibrating $\mathcal{C}_{B,\mathrm{ref}}$ with $q_{0,\mathrm{ref}}\simeq -0.527$ gives $w_{\mathrm{DE},0}\simeq -1.003$, $z_t\simeq0.442$, $j_0\simeq1.486$. Two-dimensional $(n,\Delta)$ maps show opposite effects on $w_{\mathrm{DE},0}$ but same direction on acceleration onset. We compare expansion histories with 36 cosmic-chronometer measurements ($0.07\leq z\leq1.965$), using DESI covariance and asymmetric error at $z=0.8$. Comparison is conditional for fixed trajectories, without fitting; Hubble statistic varies modestly. Results provide a consistent background realization of Ricci-cutoff BHDE in $f(Q,L_m)$ gravity and motivate future perturbation and multi-probe studies.

Within the framework of gravitational thermodynamicization, we investigate the propagation of charged scalar fields in static two-dimensional black-hole spacetimes. Starting from the scalar-field action, we derive the exact radial wave equation and show that a neutral, massless, minimally coupled scalar field in a genuinely two-dimensional geometry exhibits neither an angular-momentum barrier nor superradiant amplification. For a charged scalar field, the condition for amplification is governed by the electrostatic potential evaluated at the event horizon. In the case of the charged two-dimensional string black hole, the horizon electrostatic potential is directly related to the Hawking temperature, implying that the superradiant frequency window is determined by the thermodynamic state of the black hole. We further formulate a near-horizon residue criterion that provides a coordinate-independent characterization of the superradiant threshold. When a reflecting outer boundary is imposed, necessary frequency conditions for unstable modes are derived, together with an upper bound on their growth rates. Numerical calculations verify the corresponding flux relation and clearly distinguish superradiant scattering from genuine superradiant instability.

We propose an optical-fiber implementation of the Observer-Split source framework for finite rotating systems in extended Aharonov-Bohm electrodynamics. A covariantly conserved current, rewritten in a rotating 3+1 split, produces the observer-adapted source term $I_{\rm split}=N^{-1}D_i(\rho\beta^i)$, which in the weak-field rigid-rotation limit becomes $I_G=\Omega\partial_\phi\rho$. We use an optically gated rotating aluminum disc to create a localized, calibratable induced density, with the optical evanescent/tunneling coefficient acting only as a control gate rather than as a charge density. The resulting source scales as $I_{\rm opt}\simeq\Omega\partial_\phi\rho_{\rm ind,Al}$ and reverses sign under CW/CCW reversal. The proposed demonstrator combines ON/OFF gating, a localized 10–20 degree active sector, uniform-source suppression, material and dummy controls, quantitative null bounds, and independent density calibration. The residual response is parameterized by the experimentally identifiable product $\Lambda_{\rm opt}=\kappa_{\rm opt}\chi_{\rm Al}$, so both positive and null measurements constrain the phenomenology without assuming an uncalibrated force amplitude. Historical rotating magnetic systems, including the Roshchin-Godin report, are used only as benchmarks and not as evidence. The work is a falsifiable protocol for testing anomalous gravitational-response signatures; it reports no anomalous-weight measurement and makes no claim of evidence for a gravitational anomaly or for extended Aharonov-Bohm electrodynamics.

The black hole information paradox exposes a fundamental contradiction between quantum unitarity and semiclassical gravity. Although the entanglement island paradigm is capable of reproducing the Page curve, the physical essence of quantum extremal surfaces and the microscopic mechanism of information transfer have yet to be clarified. Taking quantum information as a fundamental conserved quantity and adopting the principle of information curvature scaling, this paper argues that no singularity exists inside a black hole. Instead, there exist information surfaces encoding quantum information and attached overflow field structures. The model divides black hole evaporation into two stages: the unsaturated stage and the saturated stage. During the unsaturated stage, Hawking radiation dissipates the overflow field, resulting in a steady increase of entanglement entropy. In the saturated stage, the overflow field is completely exhausted. The information surface then undergoes fragmentation and reconstruction, emitting high-energy particles carrying quantum information and driving a gradual decline in entanglement entropy. At the very final stage of black hole evaporation, all residual quantum information and mass are released entirely through a quantum outburst. This model establishes the physical correspondences between the event horizon and the quantum extremal surface, as well as between the information surface and the entanglement island, which can provide some phenomenological constraints for quantum gravity theories.

The law of conservation of energy can be stated: Energy can neither be created or destroyed but only converted to from one form to another. Laboratory experiments demonstrating that no energy is lost or gained during a conversion have been rare. Interestingly, there is a close connection between energy conservation, Lorentz violation and the possibility of a second dimension of time. We explore this connection within a model of Lorentz invariance that incorporates a second dimension of time. The model's Lorentz transformation matrix reduces to the well-known one-dimension of time version in the limit of a parameter that defines the relative size of the extra dimension. If the parameter is finite, one might misinterpret the energy equivalence of mass or observe a deviation from the accepted time dilation formalism. We explore different experimental limits on this new parameter including Lorentz violating parameters from the Standard-Model Extension.

This study applies Duan's topological current $\phi$-mapping theory to investigate a newly proposed charged modified AdS black hole using the Rényi entropy formalism, examining its thermodynamic properties across the canonical, mixed, and grand canonical ensembles.} Electric and magnetic charges are fixed in the canonical ensemble, whereas the mixed ensemble incorporates electric and magnetic potentials. The grand canonical ensemble, meanwhile, ensures consistency by employing these potentials exclusively. Initially, we compute topological charges by identifying critical points in each ensemble. In both the canonical and mixed ensembles, we identify a conventional critical point with a topological charge of $-1$. We then model the black hole's domain in the AdS regime as a topological defect in thermodynamic space and analyze its local and global topology by calculating the winding numbers at these defect locations. {Interestingly, the canonical and mixed ensembles exhibit identical black hole topologies, each possessing a total topological charge of $1$ within the framework of the Rényi entropy.} Finally, we characterize the canonical, mixed, and grand canonical ensembles based on the presence of generation/annihilation points: the canonical ensemble has one such point, the mixed ensemble has a negative one, and the grand canonical ensemble has none.

Magnetic flux can move, and moving magnetic flux is associated with induced electric fields. Where there are multiple sources of flux, the induced electric field is the vector resultant of the induced fields attributable to the fluxes acting individually; it is not necessarily associated with the resultant magnetic field. The key insight is that flux can move through regions in which the magnetic field itself vanishes, much as electric charge can move (as electric current) through a region in which the net charge density is zero. For this reason, moving flux can account for the induced emf around a long solenoid in which the current is changing. It also accounts for unipolar induction, and this account is testable.

Modified Newtonian Dynamics (MOND) generally resolves the need for dark matter in galaxy rotation curves introducing a single new constant of acceleration $a_0$. It is well known that increasing $a_0$ by a factor of a few can alleviate the residual mass discrepancies that MOND leaves in galaxy clusters. Within a parameter-free Machian interpretation of MOND, in which $a_0\sim GM_u/R_u^2$ arises from the scalar sum of inverse-square distance gravitational mass contributions in the universe, we promote $a_0$ to a variable influenced by mass external to a locally enclosed region in the spherically symmetric case. Instead of a boost of $a_0$ in terms of gravitational potentials as in EMOND, we show that a boost in terms of this directionless inverse-square field roughly amounts to the boost needed to accommodate the mass discrepancies of MOND in galaxy clusters. We conclude by beginning to generalize the proposed formulation beyond spherical symmetry.

We investigate a particular case of the extended exponential infrared f(T) teleparallel gravity, in which the geometric sector naturally produces an effective dark-energy density that evolves from negative values in the past to positive values at late times. This behaviour could be motivated by observational results providing a compelling motivation for a geometric, sign-changing dark-energy scenario within modified gravity. We demonstrate that the parameter space of the present model contains only six parameters similar to $\Lambda$CDM. A Markov Chain Monte Carlo (MCMC) analysis using Planck, DESI, and Type Ia supernova data yields a well-constrained transition redshift of $z_{\rm tr} \gtrsim 1.62$, accompanied by a transition in the effective equation of state to the phantom regime ($w < -1$) for $z < z_{\rm tr}$. Since the effective dark energy originates from modified geometric degrees of freedom, no instabilities or violations of energy conditions arise. The model naturally accounts for the $H_0$ tension, where Planck+DESI data combination gives $H_0 = 72.13 \pm 0.28 \text{ km s}^{-1} \text{ Mpc}^{-1}$ in a better agreement with local measurements than $\Lambda$CDM which gives $H_0 = 68.46 \pm 0.30 \text{ km s}^{-1} \text{ Mpc}^{-1}$. However, the model is disfavored in comparison to $\Lambda$CDM in terms of the values of $\chi^2$ of the bestfit parameters. We discuss the result among other issues related to CMB-BAO tension.

General Relativity (GR) can be effectively examined in the low-velocity, weak-field limit, where its inherently tensorial structure simplifies to a vector-based formulation closely analogous to classical electrodynamics. This correspondence becomes particularly clear when both theories are expressed within a field-free, interaction-based framework, in which the leading relativistic corrections emerge naturally as velocity- and acceleration-dependent modifications to the static interaction. As a result, several predictions of GR can be derived using familiar techniques from electrodynamics, provided the relevant phenomena remain within the regime of validity of the approximation. This structural analogy facilitates a conceptual understanding of GR enabling the introduction of its core ideas even in an introductory level course, the single exception being the treatment of radiation, which requires tools at more advanced level. Building on this pedagogical framework, the incorporation of special relativity (SR) and the equivalence principle enables concise and transparent derivations of gravitational time dilation, as well as its immediate consequences, including light deflection and gravitational frequency shifts. A detailed exposition of this material is provided in the supplementary material.

Protons and neutrons are the smallest forms of measurable matter, and each nucleon has 3 up (+2/3) and down (-1/3) quarks. Quarks treated as point-like particles within polygonal geometries model the structures of stable nuclides through $^{36}$Ar. The model derives from the proton's radius (r=0.8414 fm), the hadron's prolate spheroid shape (from the $\Delta(1232)$ resonance), and the separation distance between bound nucleons ($\approx$0.8 fm, from the Argonne $v_{18}$ $NN$ potential). The prolate nucleon's spatial extent arises from its 3 quarks, which implies a qualitatively linear quark sequence. Spin-spin forces repel the like-flavored quarks to opposite ends of the nucleon, leaving the unlike quark in the middle. Quark-to-quark distance within the nucleon corresponds to the nucleon's radius. Nucleons link by quark-to-quark interactions to form proton-neutron short-range correlated pairs (pn SRC pairs), separated by a distance equal to the proton's radius. Alternating nucleons produce regularly alternating up/down quark sequences. We contemplate structures for each stable nuclide through $^{36}$Ar and include the one whose rotational radius (from the regular polygon radius formula) best correlates with its accepted charge radius (r(31)=0.98, p<0.001). Nucleon alternation makes pn SRC pairs and produces the equal numbers of protons and neutrons (Z=N) in the isotopes $^{4}_{2}$He, $^{12}_{6}$C, $^{14}_{7}$N, $^{16}_{8}$O, $^{20}_{10}$Ne, $^{24}_{12}$Mg, $^{28}_{14}$Si, and $^{32}_{16}$S, comprising 99.5% of stable baryonic matter. Bilateral structural symmetry emerges as a sensitive and specific predictor of cosmic abundance. Opposing deuteron-deuteron alternating quark charge sequences produce alternating and unequal electromagnetic fields capable of modelling the close-range attraction and far-range repulsion of the fusion potential curve and Coulomb potential energy barrier.