The European Physical Journal C最新文献

In this work, we study the restricted phase space thermodynamics (RPST) of charged static and rotating black holes in f(R) gravity. By keeping the cosmological constant fixed and introducing the central charge C with its conjugate chemical potential (mu ), RPST allows the black-hole mass to be interpreted as internal energy. We compute the corresponding thermodynamic quantities and analyse the T–S and F–T behaviours, which show the characteristic non-monotonicity and swallow-tail structures associated with first-order phase transitions, along with a second-order critical point. To confirm these results, we use the Legendre-invariant framework of geometrothermodynamics (GTD) and show that divergences of the GTD scalar curvature coincide with those of the specific heat, providing geometric confirmation of the phase structure in f(R) gravity.

We propose the experimental simulation of cosmological perturbations governed by a Planck-scale induced Lorentz violating dispersion, aimed at distinguishing between early-universe models with similar power spectra. Employing a novel variant of the scaling approach for the evolution of a Bose–Einstein condensate with both contact and dipolar interactions, we capture the hitherto unobserved phenomenon of trans-Planckian damping. We show that scale invariance, and in turn, the duality of the power spectrum is subsequently broken at large momenta for an inflating gas, and at small momenta for a contracting gas. We thereby furnish a Planck-scale sensitive approach to analogue quantum cosmology that can readily be implemented in the quantum gas laboratory.

We analyze quasi-periodic oscillation data from selected X-ray binary systems hosting black holes. To model the spacetime geometry, we resort to the static Sen solution—originally derived in the framework of heterotic string theory—which reduces to the Schwarzschild spacetime for vanishing electric charge. By fitting the observed frequencies within the relativistic precession model, we constrain the mass and charge parameters of the Sen black hole and discuss their astrophysical implications, particularly in distinguishing classical black holes from their string-inspired counterparts.

In this paper, we perform a Bayesian statistical fit to estimate the free parameters of a nonsingular black hole in conformal gravity by employing megamaser astrophysical data of the supermassive black hole hosted at the center of the active galactic nucleus of NGC 4258. This estimation has been carried out by taking into account a general relativistic approach, which makes use of the positions on the sky of the photon sources and the frequency shift observations from the water megamaser system in circular motion around the black hole. Within the framework of conformal gravity, a way to eliminate the singularity at (r=0) from the Schwarzschild spacetime is by introducing a conformal factor characterized by a length scale parameter l and an integer parameter N. Therefore, the spacetime geometry depends on the mass of the black hole, and the conformal gravity parameters l and N. In this work, we estimate the mass-to-distance ratio M/D and the length scale ratio l/D with fixed values of the integer parameter (N=1,2), considering the geodesics of conformally/non-conformally coupled massive particles. This method leads to posterior Gaussian distributions for all parameters, thus yielding a most probable value for the parameter l for both conformally/non-conformally coupled particles, in contrast to previous constraints based on X-ray astrophysical data, where an upper bound for the parameter l has been established. Furthermore, we obtain new physical properties regarding the existence of the ISCO radius for this nonsingular spacetime in the case of non-conformally coupled particles.

In this work, we discuss both relativistic and perturbative QCD corrections to the transition form-factor (mathcal{F}_{eta _Q}{(t_1,t_2)}) for the process (gamma ^*(q_1) gamma ^*(q_2) leftrightarrow eta _Q(P)) with dependencies on the normalised photon virtualities (t_1=q_1^2/m_Q^2) and (t_2=q_2^2/m_Q^2), where (m_Q) is the heavy quark mass. We resum a class of relativistic corrections to all orders in the relativistic parameter (langle v^2 rangle _{eta _Q}). In addition, we include perturbative QCD corrections up to next-to-next-to-leading order (NNLO) in the strong coupling constant (alpha _s). This involves the computation of two-loop amplitudes with two off-shell photons. We explore three different phenomenological applications of our transition form-factors for the charmonium case. We first study the ratio (vert mathcal{F}_{eta _c}{(t_1,0)} vert / vert mathcal{F}_{eta _c}{(0,0)} vert ) for the single space-like photon case and compare our results with the existing (eta _c) measurements from the Ba Bar collaboration. Secondly, we consider observables for the case of double space-like photons and discuss the impact of the different corrections. The NNLO corrections for this case are presented here for the first time in the literature. Finally, we revisit the decay width (Gamma [eta _c rightarrow gamma gamma ]) and compare it with the existing PDG value.

Accretion processes around black holes play a central role in high-energy astrophysics by governing compact object growth and driving luminous emissions across the electromagnetic spectrum. In this work, we propose a theoretical framework in which the local flow of time near the event horizon acquires a fractal structure, potentially arising from quantum gravitational fluctuations at Planckian length scales. This fractal temporal behavior, characterized by a scaling relation (t_f = t^{alpha }) with (0 < alpha le 1), modifies the time evolution of surface density in viscous accretion disks. We derive a generalized diffusion equation incorporating the fractal-time exponent (alpha ) and perform numerical simulations across a wide range of black-hole masses ((5,M_odot ) to (10^9,M_odot )) and accretion rates (0.01–(1.0,dot{M}_textrm{Edd})). Our results reveal enhanced modulation in the accretion luminosity and the emergence of quasi-periodic oscillations (QPOs) in the X-ray light curves. The predicted QPO frequencies, which range from 4–(8,textrm{Hz}) for stellar-mass black holes, scale with the fractal exponent and follow (nu _textrm{QPO}propto M_textrm{BH}^{-alpha }) (classical limit (alpha =1)), remaining within the detection capabilities of current instruments such as NICER, XMM-Newton, and NuSTAR. These findings indicate that microscopic spacetime fluctuations may leave macroscopic imprints on accretion dynamics, thereby providing an observational probe of fractal-time behavior near black holes. This work offers a testable connection between quantum gravitational microphysics and observable X-ray variability.

We calculate the one-loop electroweak corrections to the gravitational form factors of the Higgs boson and discuss the interpretation of the obtained results.

Recent discovery of a compact binary coalescence through GW230529 by LIGO has indicated the merger event of a compact object of mass between (2.5{-}4.5~M_{odot }) with a neutron star of mass between (1.2{-}2.0~M_{odot }). The mass of the unknown compact object makes it within the heaviest neutron star never tracked out or the lightest black hole ever detected. Here, we have shown that such a mass gap neutron star with this observed mass ((2.5{-}4.5~M_{odot })) can be explained consistently by f(R) gravity. We have also adopted the presence of pressure anisotropy inside the neutron star which supports a massive neutron star with mass more than (2.6~M_{odot }), compatible with LIGO data (GW190814). Further, the modified Tollman–Oppenheimer–Volkoff equations have acknowledged such a compact stellar structure that can produce gravitational wave echoes (frequencies remain in the range of (3{-}6) kHz).

In this paper, we explore quasibound states (QBS), scalar clouds, Hawking radiation, superradiance, and greybody factors of relativistic massive phonon modes in a photon-fluid rotation black hole. We investigate quasibound states and scalar clouds using exact eigensolutions to the analog Klein–Gordon equation in an analog black hole background and revisit the Wentzel–Kramers–Brillouin (WKB) upper bound on the scalar clouds’ energy ratio. Using the obtained exact radial solution, we use the Damour–Ruffini method to calculate the power spectrum of the analog black hole’s Hawking radiation. We then use the analytical asymptotic matching technique (AAM) to investigate the analog black hole’s superradiance for low-energy massive photon scattering, resulting in the analytical amplification factor and the greybody factor formulas of the analog black hole. We discover that the analog black hole in the photon-fluid model is superradiant, with an energy range of (varpi< omega <m_ell Omega _H). As a result, the greybody factors are negative for co-rotating modes in the superradiant regime.

This work presents a comprehensive investigation of a novel cosmological model that includes the Modified Chaplygin Gas (MCG) equation of state with gravitationally induced matter creation and bulk viscous dissipation in a spatially flat Friedmann–Lemaître–Robertson–Walker spacetime. The MCG fluid is characterized by an exotic equation of state (p = Arho - C/rho ^alpha ). The matter creation rate is taken as (varGamma = 3beta H) and the bulk viscous pressure as (pi = -3Hxi _0 rho _m^{1/2}). We derive the modified Friedmann equations and obtain an analytical expression for the Hubble parameter H(z), which is then used to reconstruct the evolutionary trajectories of key cosmological parameters. The model parameters are constrained using two observational datasets: DS1 (Pantheon+ + Cosmic Chronometers + DESI BAO + (sigma _8)) and DS2 (DS1 + R22). Our results indicate that the proposed hybrid model successfully generates a transition from decelerated to accelerated expansion, consistent with current observations. Notably, when the R22 prior is included the best-fit value of (H_0) shifts towards the local SH0ES determination; the hybrid model is flexible enough to accommodate this higher (H_0) while preserving a good fit to the geometric datasets, thereby reducing the level of tension in joint analyses between local and background probes, although it does not dynamically resolve the (H_0) discrepancy by itself. Furthermore, we perform a rigorous thermodynamic analysis of the model by testing the Generalized Second Law (GSL) of thermodynamics. We use the information cretria, like Akaike and Bayesian to check the model stability. This work establishes a physically motivated, observationally viable, and thermodynamically consistent alternative to the standard (varLambda )CDM paradigm.