Modern Physics Letters A

We discuss equilibration process in expanding Universes as compared to the thermalization process in Minkowski spacetime. The final goal is to answer the following question: Is the equilibrium reached before the rapid expansion stops and quantum effects have a negligible effect on the background geometry or stress–energy fluxes in a highly curved early Universe have strong effects on the expansion rate and the equilibrium is reached only after the drastic decrease of the spacetime curvature? We argue that consideration of more generic non-invariant states in theories with invariant actions is a necessary ingredient to understand quantum field dynamics in strongly curved backgrounds. We are talking about such states in which correlation functions are not functions of such isometry invariants as geodesic distances, while having correct UV behavior. The reason to consider such states is the presence of IR secular memory effects for generic time-dependent backgrounds, which are totally absent in equilibrium. These effects strongly affect the destiny of observables in highly curved spacetimes.

The Fradkin–Schwinger functional methods to represent a Green function in an external gravitational field are used to study the eikonal and the next-to-eikonal limit, including the nonlinear gravitational interactions, of the scattering amplitudes of an ultra-relativistic scalar particle on a static super-massive scalar target in the nearly forward limit. The functional approach confirms the exponentiation of the leading eikonal which also applies to the first non-leading power in the energy of the light particle, moreover includes the interaction at impact parameter much larger than the Schwarzschild radius associated with the center of mass energy in the ultra-relativistic limit.

Magnetars are comparatively young neutron stars with ultra-strong surface magnetic field in the range $10^{14}\text{–}10^{16}\mathrm{\text{G}}$. The old neutron stars have surface magnetic field somewhat less $\sim$$10^8\mathrm{\text{G}}$ which clearly indicates the decay of field with time. One possible way of magnetic field decay is by ambipolar diffusion. We describe the general procedure to solve for the ambipolar velocity inside the star core without any approximation. With a realistic model of neutron star, we determine the ambipolar velocity configuration inside the neutron star core and hence find the ambipolar decay rate, associated timescales and the magnetic energy dissipated which is consistent with the magnetar observations.

This paper is devoted for the formulation of new anisotropic solutions for non-static spherically symmetric self-gravitating systems through gravitational decoupling technique. Initially, we add a gravitational source in the perfect matter distribution for inducing the effects of anisotropy in the considered model. We then decouple the field equations through minimal geometric deformation approach and derive three new anisotropic solutions. Among these, two anisotropic solutions are evaluated by applying specific constraints on anisotropic source and the third solution is obtained by employing the barotropic equation of state. The physical acceptability and stability of the anisotropic models are investigated through energy conditions and causality condition, respectively. We conclude that all the derived anisotropic solutions are physically viable as well as stable.

This paper explores the influence of special type of higher order generalized uncertainty principle on the thermodynamics of five-dimensional black hole in Einstein–Gauss–Bonnet gravity coupled to nonlinear electrodynamics. We examine the corrected thermodynamical properties of the black hole with some interesting limiting cases $k\to 0$ and $\alpha \to 0$ and compared our results with usual thermodynamical relations. We observe that the influence of GUP correction stabilizes the BH and BH solution remains physical throughout the region of horizon radius. In this framework, we also uncover the relationship of shadow radius and quasinormal modes of the mentioned black hole. We conclude that shadow radius of our considered black hole is a perfect circle and it decreases with increasing values of charge and Gauss–Bonnet parameter. We also verify the inverse relation between the quasinormal modes frequencies and shadow radius, i.e. quasinormal modes should increase with increasing values of Gauss–Bonnet parameter and electric charge.

The proton radius puzzle has motivated several new experiments that aim to extract the proton charge radius and resolve the puzzle. Recently, PRad, a new electron–proton scattering experiment at Jefferson Lab, reported a proton charge radius of $0.831\pm 0.007_{\mathrm{\text{statistical}}}\pm 0.012_{\mathrm{\text{systematic}}}$. The value was obtained by using a rational function model for the proton electric form factor. We perform a model-independent extraction using $z$-expansion of the proton charge radius from PRad data. We find that the model-independent statistical error is more than 50% larger compared to the statistical error reported by PRad.

In this work, we would like to apply the asymptotic iteration method (AIM) to a newly proposed Morse-like deformed potential introduced recently by Assi, Alhaidari and Bahlouli.${}^{23}$ This interesting potential can support bound states and/or resonances. However, in this work, we are only interested in bound states. We considered several choices of the potential parameters and obtained the associated spectrum. Finally, we study the small deformation limit at which this finite spectrum system will transition to infinite spectrum size.

The discrete phase space continuous time representation of relativistic quantum mechanics involving a characteristic length $l$ is investigated. Fundamental physical constants such as $\hslash$, $c$, and $l$ are retained for most sections of the paper. The energy eigenvalue problem for the Planck oscillator is solved exactly in this framework. Discrete concircular orbits of constant energy are shown to be circles $S_n^1$ of radii $2E_n=\sqrt{2n+1}$ within the discrete $(1+1)$-dimensional phase plane. Moreover, the time evolution of these orbits sweep out world-sheet like geometrical entities $S_n^1\times ℝ\subset {ℝ}^2$ and therefore appear as closed string-like geometrical configurations. The physical interpretation for these discrete orbits in phase space as degenerate, string-like phase cells is shown in a mathematically rigorous way. The existence of these closed concircular orbits in the arena of discrete phase space quantum mechanics, known for the non-singular nature of lower order expansion $S^{\#}$ matrix terms, was known to exist but has not been fully explored until now. Finally, the discrete partial difference-differential Klein–Gordon equation is shown to be invariant under the continuous inhomogeneous orthogonal group ${ℐ}[O(3,1)]$.

In this work, we explore a generalization of the Dirac and Klein–Gordon (KG) oscillators, provided with a deformed linear momentum inspired in nonextensive statistics, that gives place to the Morse potential in relativistic contexts by first principles. In the (1 + 1)-dimensional case, the relativistic oscillators are mapped into the quantum Morse potential. Using the Pekeris approximation, in the (3 + 1)-dimensional case, we study the thermodynamics of the S-waves states (l = 0) of the H₂, LiH, HCl and CO molecules (in the non-relativistic limit) and of a relativistic electron, where Schottky anomalies (due to the finiteness of the Morse spectrum) and spin contributions to the heat capacity are reported. By revisiting a generalized Pekeris approximation, we provide a mapping from (3 + 1)-dimensional Dirac and KG equations with a spherical potential to an associated one-dimensional Schrödinger-like equation, and we obtain the family of potentials for which this mapping corresponds to a Schrödinger equation with non-minimal coupling.