Abstract We investigate the motion of test particles and the properties of accretion disks in rotating, accelerating black hole spacetimes with a non-zero cosmological constant. To do so, we explore the impact of both rotation and acceleration on massive particle dynamics in motion around these configurations. In this respect, we derive the geodesic equations in the Plebański-Demiański spacetime and analyse the characteristics of circular orbits, including the innermost and outermost stable circular orbits. Accordingly, we find that acceleration produces a small correction to the innermost stable circular orbit (ISCO) in the slowly accelerating regime, while its influence becomes more pronounced for the outermost stable circular orbit (OSCO) and hence for the radial extension of the stable-orbit region. Further, we examine the precession of non-circular orbits and find that the precession is in the same direction as the rotation of the test particle regardless of the direction of the black hole spin. We also investigate the thermal spectra of geometrically thin, optically thick accretion disks described by the Novikov-Thorne model. We consider both co-rotating and counter-rotating disks and show that the radiative flux and luminosity are significantly larger for co-rotating disks. We compare the spectral features and luminosity of accretion disks around accelerating black holes with those around non-accelerating Kerr black holes, revealing that acceleration generally reduces the luminosity and flux of emitted light. Our results provide insights into the complex interplay between black hole acceleration, rotation, and the surrounding accretion disk dynamics.
Abstract The origin of the small asymmetry in the abundance of matter and antimatter in the very early universe, described by the Baryon Asymmetry Factor η = 8.65 × 10 -11 , is one of the big unanswered questions of contemporary physics. Gravitational baryogenesis postulates the baryon-antibaryon asymmetry is generated by a coupling between the baryon current and the gradient of the Ricci scalar R . As this coupling is zero in General Relativity for a radiation dominated flat early Universe, more generalized theories of gravity are required. The present study investigates the feasibility of gravitational baryogenesis during the inflationary phase of two f ( R ) modified theories of gravity: the widely used Starobinsky f ( R ) = R + R 2 / M 2 model, and the recently proposed power-law model f ( R ) = c 1 R 2+ k /4 + c 2 R + c 3 of Odintsov and Oikonomou (2025) that is constructed from the slow-roll inflation parameters, and fits the new high-multipole CMB observations reported by the Planck and ACT collaborations for k ∼ -0.03. Rather than use the Jordan frame in which these cosmologies have been formulated, the present investigation is undertaken in the Einstein frame, which is obtained from the Jordan frame by a conformal transformation Ω, which introduces the scalaron field ϕ = κ -1 √(6)lnΩ. The motion of the scalaron is studied for the slow roll inflationary era using analytic approximate solutions, from which expressions are obtained for R and hence η . Some of the expressions for the Starobinsky model were obtained first by Motohashi and Nishizawa (2012) but the expressions for the power-law model of Odintsov and Oikonomou and its generalization are new. Although the values of η calculated for both models are quite close to the observed value, they are based upon several assumptions that qualify these results. The asymmetries are generated during the slow roll inflation era and, for values generated N e-folds before the end of inflation, must be diluted by the factor Δ ≲ 10 e -3 N , making agreement with observation difficult to achieve unless baryogenesis occurs at the end of the inflation era. The calculations also assume rapid thermalization of the plasma of the gravitationally produced particles, and that the interaction rate of the baryon-violating processes is greater than the expansion rate of the Universe until decoupling. The present calculations strongly violate these assumptions and would require significant variation of input parameters, which is excluded by CMB observations, to obtain agreement. A complete treatment of thermalization of the gravitationally produced plasma, baryon-number violating freeze-out, and entropy dilution is required to establish whether or not gravitational baryogenesis during slow-roll inflation is a viable mechanism for producing the observed baryon asymmetry of the Universe for these inflationary f ( R ) cosmologies.
Abstract We investigate the effect of local cosmic voids on low-redshift measurements of the Hubble rate in flat w 0 w a CDM cosmologies. Using a hydrodynamical model for isolated spherical inverse top-hat underdensities, we compute the void-induced Hubble shift as a function of redshift, enclosed density contrast δ E and cosmological parameters. We find that the effect is mainly controlled by the matter sector, through δ E and Ω m,0 , while dynamical dark energy gives only subdominant late-time corrections. For a Planck-calibrated ΛCDM background, matching the SH0ES value requires a present-day void with δ E ( z = 0)≃ -0.44, substantially deeper than the KBC-like local underdensity. A KBC-like void lowers the SH0ES-Planck discrepancy to about 2 σ , but is not deep enough to fully reconcile the two measurements. Allowing for dynamical dark energy, including regions motivated by recent DES and DESI analyses, changes this result only at the percent level. We also show that the reported redshift dependence of locally inferred H 0 values can be represented phenomenologically by an effective enclosed matter profile. This reconstruction should be interpreted as a consistency test of local-structure effects rather than as explanation for an evolving background value of H 0 . Overall, local underdensities can affect low-redshift Hubble-rate inferences, but they do not resolve the Hubble tension within the spherical void setup considered here.
We investigate a radiative seesaw model under a non-holomorphic modular S3 flavor symmetry, addressing neutrino masses, dark matter candidates, and lepton flavor violations. Neutrino masses arise at the one-loop level, and we confront the model with neutrino oscillation data, lepton flavor violation bounds, and relic density requirements through a chi-square analysis. By incorporating the latest JUNO results, we find that the allowed parameter space is strongly constrained: For the normal hierarchy, both fermionic and bosonic dark matter scenarios remain viable but highly localized, whereas for the inverted hierarchy with fermionic dark matter no allowed region survives. These findings demonstrate that JUNO provides decisive constraints and that our framework is highly predictive.
We investigate the impact of accretion onto supermassive black holes on the density profiles of a fuzzy dark matter soliton core at the center of a dark matter halo. Treating the supermassive black hole at the galactic center as a point mass, we numerically solve the Schr & ouml;dinger-Newton equation for the scalar field. We find that the time-dependent perturbation induces a pronounced squeezing of the soliton profile, simultaneously shrinking the core size and increasing the central density. These results clarify how black hole growth can reshape fuzzy-dark-matter structures and may help reconcile tensions in observed galactic core properties.
