A de-Sitter weak gravity conjecture

The study of de-Sitter Reissner–Nordstrøm black holes allows us to uncover a Weak Gravity Conjecture in de-Sitter space. It states that for a given mass [Formula: see text] there should be a state with a charge [Formula: see text] bigger than a minimal value [Formula: see text], depending on the mass and the de-Sitter radius [Formula: see text], in Planck units. This reproduces the well-known flat space–time result [Formula: see text] in the large radius limit (large [Formula: see text]). In the highly curved de-Sitter space, ([Formula: see text]) [Formula: see text] behaves as [Formula: see text]. Finally, we discuss the case of backgrounds from gauged R-symmetry in [Formula: see text] supergravity. This paper is based on [I. Antoniadis and K. Benakli, Fortsch. Phys. 68, 2000054 (2020), arXiv:2006.12512 [hep-th]].

Ultra-spinning Chow’s black holes in six-dimensional gauged supergravity and their properties

By taking the ultra-spinning limit as a simple solution-generating trick, a novel class of ultra-spinning charged black hole solutions has been constructed from Chow’s rotating charged black hole with two equal-charge parameters in six-dimensional $$ \mathcal{N} $$ N = 4 gauged supergravity theory. We investigate their thermodynamical properties and then demonstrate that all thermodynamical quantities completely obey both the differential first law and the Bekenstein-Smarr mass formula. For the six-dimensional ultra-spinning Chow’s black hole with only one rotation parameter, we show that it does not always obey the reverse isoperimetric inequality, thus it can be either sub-entropic or super-entropic, depending upon the ranges of the mass parameter and especially the charge parameter. This property is obviously different from that of the six-dimensional singly-rotating Kerr-AdS super-entropic black hole, which always strictly violates the RII. For the six-dimensional doubly-rotating Chow’s black hole but ultra-spinning only along one spatial axis, we point out that it may also obey or violate the RII, and can be either super-entropic or sub-entropic in general.

A comparative analysis of self-consistent charged anisotropic spheres

This study is devoted to exploring the charged stellar structures under embedded space–time using the Karmarkar condition. For this, spherically symmetric space–time with the anisotropic source of fluid possessing an electric charge has been incorporated. Further, the Bardeen and Reissner–Nordstrom geometries have been employed as exterior space–time to calculate the values of the involved constants. The interior solutions of a stellar object have been worked out with the observational mass [Formula: see text], and [Formula: see text] km. It is argued that the acquired solutions accomplish all the necessary conditions for self-consistent charged stars. It has been noted through the detailed graphical analysis that our obtained solutions are physically stable and self-consistent with the best degree of accuracy for [Formula: see text], where parameter [Formula: see text] is involved in the model under discussion. Beyond this bound [Formula: see text], the realistic solutions of stellar models under discussion could not be found. After perceiving the marginal dissimilarities between our proposed models in both cases, Andreasson’s limit [Formula: see text], critically important for the stellar structures, has been achieved in both the models under investigation. Lastly, it is established that the parameter [Formula: see text] has a substantial effect on worked-out solutions under the employment of Bardeen and Reissner–Nordstrom’s stellar structures.

Nonlinear Stability of Equilibrium Points in the Planar Equilateral Restricted Mass-Unequal Four-Body Problem

In this paper, we investigate the stability of equilibrium points for the planar restricted equilateral four-body problem in the case that one particle of negligible mass is moving under the Newtonian gravitational attraction of three positive masses [Formula: see text], [Formula: see text] and [Formula: see text] (called primaries). These always lie at the vertices of an equilateral triangle (Lagrangian configuration) and move with constant angular velocity in circular orbits around their center of masses. We consider the case where all the primaries have unequal masses, and investigate the nonlinear stability (in the sense of Lyapunov) of the elliptic equilibrium for the specific values of the mass [Formula: see text] and [Formula: see text] of the primary, fixed on the horizontal axis. Moreover, the [Formula: see text][Formula: see text]:[Formula: see text][Formula: see text] four-order resonant cases are determined and the stability is investigated. In this study, Markeev’s theorem and Arnold’s theorem become key ingredients.

The Hawking black-hole radiation spectrum has a short tail

It is proved that the Hawking emission spectrum of a semiclassical Schwarzschild black hole of mass [Formula: see text] has a sharp cut at the frequency scale [Formula: see text]. In particular, taking into account the nonlinear gravitational coupling between the tunneled Hawking quanta and the emitting black hole, it is explicitly shown that the upper bound [Formula: see text] on the energies of the emitted Hawking quanta is a direct consequence of the famous Thorne hoop relation.

On gapped continuum resonance spectra

In this work, we study a warped five-dimensional (5D) model with ultraviolet (UV) and infrared (IR) branes, that solves the hierarchy problem with a fundamental 5D Planck scale [Formula: see text], and curvature parameter [Formula: see text], of the order of the 4D Planck mass [Formula: see text] TeV. The model exhibits a continuum of Kaluza–Klein (KK) modes with different mass gaps, at the TeV scale, for all fields. We have computed Green’s functions and spectral densities, and shown how the presence of a continuum KK spectrum can produce an enhancement in the cross-section of some Standard Model processes. The metric is linear near the IR, in conformal coordinates, as in the linear dilaton (LD) and 5D clockwork models, for which [Formula: see text] TeV. We also analyze a pure (continuum) LD scenario, solving the hierarchy problem with more conventional fundamental [Formula: see text] and [Formula: see text] scales of the order of [Formula: see text], and a continuum spectrum.