Asymptotic quasinormal frequencies of different spin fields in d-dimensional spherically-symmetric black holes

While Hod's conjecture is demonstrably restrictive, the link he observed between black hole (BH) area quantisation and the large overtone ($n$) limit of quasinormal frequencies (QNFs) motivated intense scrutiny of the regime, from which an improved understanding of asymptotic quasinormal frequencies (aQNFs) emerged. A further outcome was the development of the ``monodromy technique", which exploits an anti-Stokes line analysis to extract physical solutions from the complex plane. Here, we use the monodromy technique to validate extant aQNF expressions for perturbations of integer spin, and provide new results for the aQNFs of half-integer spins within higher-dimensional Schwarzschild, Reissner-Nordstr{\"o}m, and Schwarzschild (anti-)de Sitter BH spacetimes. Bar the Schwarzschild anti-de Sitter case, the spin-1/2 aQNFs are purely imaginary; the spin-3/2 aQNFs resemble spin-1/2 aQNFs in Schwarzschild and Schwarzschild de Sitter BHs, but match the gravitational perturbations for most others. Particularly for Schwarzschild, extremal Reissner-Nordstr{\"o}m, and several Schwarzschild de Sitter cases, the application of $n \rightarrow \infty$ generally fixes $\mathbb{R}e \{ \omega \}$ and allows for the unbounded growth of $\mathbb{I}m \{ \omega \}$ in fixed quantities.

Spin of primordial black holes in the model with collapsing domain walls

The angular momentum (spin) acquisition by a collapsing domain wall at the cosmological radiation-dominated stage is investigated. During the collapses, primordial black holes and their clusters can be born in various mass ranges. Spin accumulation occurs under the influence of tidal gravitational perturbations from the surrounding density inhomogeneities at the epoch when the domain wall crosses the cosmological horizon. It is shown that the dimensionless spin parameter can have the small values aS < 1 only for primordial black holes with masses M > 10-3M☉, whereas less massive black holes receive extreme spins aS ≃ 1. It is possible that primordial black holes obtain an additional spin due to the vector mode of perturbations.

First-order formalism for thick branes in $$f(T,{\mathscr {T}})$$ gravity

In this paper we study the thick brane scenario constructed in the recently proposed $$f(T,{\mathscr {T}})$$ f ( T , T ) theories of gravity, where T is called the torsion scalar and $${\mathscr {T}}$$ T is the trace of the energy–momentum tensor. We use the first-order formalism to find analytical solutions for models that include a scalar field as a source. In particular, we describe two interesting case in which in the first we obtain a double-kink solution, which generates a splitting in the brane. In the second case, proper management of a kink solution obtained generates a splitting in the brane intensified by the torsion parameter, evinced by the energy density components satisfying the weak and strong energy conditions. In addition, we investigate the behavior of the gravitational perturbations in this scenario. The parameters that control the torsion and the trace of the energy–momentum tensor tend to shift the massive modes to the core of the brane, keeping a gapless non-localizable and stable tower of massive modes and producing more localized massless modes.

Teleparallel gravity: Effects of torsion in 6D braneworlds

Braneworld models are interesting theoretical and phenomenological frameworks to search for new physics beyond the standard model of particles and cosmology. In this work, we discuss braneworld models whose gravitational dynamics is governed by teleparallel [Formula: see text] gravities. Here, we emphasize a codimension two-axisymmetric model, also known as a string-like brane. Likewise, in the 5D domain-wall models, the [Formula: see text] gravitational modification leads to a phase transition on the perfect fluid source providing a brane-splitting mechanism. Furthermore, the torsion changes the gravitational perturbations. The torsion produces new potential wells inside the brane core leading to a massless mode more localized around the ring structures. In addition, the torsion keeps a gapless nonlocalizable and a stable tower of massive modes in the bulk.

Probing the parameters of a Schwarzschild black hole surrounded by quintessence and cloud of strings through four standard astrophysical tests

In this paper, we concern about applying general relativistic tests on the spacetime produced by a static black hole associated with cloud of strings, in a universe filled with quintessence. The four tests we apply are precession of the perihelion in the planetary orbits, gravitational redshift, deflection of light, and the Shapiro time delay. Through this process, we constrain the spacetime’s parameters in the context of the observational data, which results in about $$\sim 10^{-9}$$ ∼ 10 - 9 for the cloud of strings parameter, and $$\sim 10^{-20}$$ ∼ 10 - 20 m$$^{-1}$$ - 1 for that of quintessence. The response of the black hole to the gravitational perturbations is also discussed.

Asymptotic quasinormal modes of string-theoretical d-dimensional black holes

We compute the quasinormal frequencies of d-dimensional spherically symmetric black holes with leading string α′ corrections for tensorial gravitational perturbations in the highly damped regime. We solve perturbatively the master differential equation and we compute the monodromies of the master perturbation variable (analytically continued to the complex plane) in different contours, in order to obtain the quasinormal mode spectra. We proceed analogously for the quasinormal modes of test scalar fields. Differently than in Einstein gravity, we obtain distinct results for the two cases.

The high sensitivity accelerometer ISA during the BepiColombo spacecraft Earth flyby: data analysis, lessons learned, and expected signals for the next

&lt;p&gt;ISA (Italian Spring Accelerometer) is a high sensitivity, relative, mass-spring accelerometer. It flies as scientific payload on-board&amp;#160; the Mercury Planetary Orbiter (MPO), module of BepiColombo ESA mission to Mercury. The accelerometer is sensitive to any acceleration, greater than 2*10&lt;sup&gt;-8&lt;/sup&gt; ms&lt;sup&gt;-2&lt;/sup&gt;Hz&lt;sup&gt;-1/2&lt;/sup&gt;, that changes&amp;#160; the spacecraft motion from a pure free fall: the, so called, Non Gravitational Perturbations (NGP). ISA data will be added, at Mercury, to the orbit determination estimation in order to help reconstructing the orbit and to make the MPO an a-posteriori free-fall satellite.&lt;/p&gt; &lt;p&gt;After the first commissioning phase, performed in between November 2018 - August 2019, and that allowed to verify the functionality of the instrument itself, the first direct verification of the correct behaviour of the system was carried out during the BepiColombo Earth Flyby. Indeed,&amp;#160; the spacecraft crossed the planet Earth shadow during the flyby and the direct Solar Radiation Pressure (SRP), the main contribution of NGP accelerations, dropped suddenly, marking a clear leap (gap)&amp;#160; in the gathered data. The scientific team compared, on the base of the satellite surface exposition and radiative characteristics, the observed &amp;#8220;drop&amp;#8221; in the acceleration, once removed&amp;#160; the on-board disturbances and inertial accelerations due to spacecraft rotations. In the talk, other ISA data recorded during the Earth Flyby are reported and expected signals for the upcoming Venus#2 Flyby and Mercury #1 Flyby are presented. &amp;#160;&lt;/p&gt;

Gravitational perturbations from NHEK to Kerr

We revisit the spectrum of linear axisymmetric gravitational perturbations of the (near-)extreme Kerr black hole. Our aim is to characterise those perturbations that are responsible for the deviations away from extremality, and to contrast them with the linearized perturbations treated in the Newman-Penrose formalism. For the near horizon region of the (near-)extreme Kerr solution, i.e. the (near-)NHEK background, we provide a complete characterisation of axisymmetric modes. This involves an infinite tower of propagating modes together with the much subtler low-lying mode sectors that contain the deformations driving the black hole away from extremality. Our analysis includes their effects on the line element, their contributions to Iyer-Wald charges around the NHEK geometry, and how to reconstitute them as gravitational perturbations on Kerr. We present in detail how regularity conditions along the angular variables modify the dynamical properties of the low-lying sector, and in particular their role in the new developments of nearly-AdS2 holography.

The theory of kinks — I. A semi-analytic model of velocity perturbations due to planet-disc interaction

A new technique to detect protoplanets is by observing the kinematics of the surrounding gas. Gravitational perturbations from a planet produce peculiar ‘kinks’ in channel maps of different gas species. In this paper, we show that such kinks can be reproduced using semi-analytic models for the velocity perturbation induced by a planet. In doing so we i) confirm that the observed kinks are consistent with the planet-induced wake; ii) show how to quantify the planet mass from the kink amplitude; in particular, we show that the kink amplitude scales with the square root of the planet mass for channels far from the planet velocity, steepening to linear as the channels approach the planet; iii) show how to extend the theory to include the effect of damping, which may be needed in order to have localized kinks.