Found 1821 results, showing the newest relevant preprints. Sort by relevancy only.Update me on new preprints

No nonminimally coupled massless scalar hair for spherically symmetric
neutral **black** **holes**

We provide a remarkably compact proof that spherically symmetric neutral

**black****holes**cannot support static nonminimally coupled massless scalar fields. Expand abstract. We provide a remarkably compact proof that spherically symmetric neutral

**black****holes**cannot support static nonminimally coupled massless scalar fields. The theorem is based on causality restrictions imposed on the energy-momentum tensor of the fields near the regular**black**-**hole**horizon.23 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Silhouettes of invisible **black** **holes**

The isolated

**black****holes**are the invisible objects in general relativity due to their physical properties. Expand abstract. Review of the genuine

**black****holes**silhouettes. The isolated**black****holes**are the invisible objects in general relativity due to their physical properties. Nevertheless, the dark silhouette of the astrophysical**black****hole**may be visible by a distant observer in the result of luminous matter lensing in the gravitational field of the**black****hole**. Depending on astrophysical conditions, it is possible to see either the**black****hole**shadow or the event horizon silhouette itself. In the case of a stationary luminous background (placed beyond the photon sphere), it is seen the**black****hole**shadow, which is a projection on the celestial sphere of the photon capture cross-section in the**black****hole**gravitational field. Meanwhile, in the case of nonstationary emitting matter in the inner part of the thin accretion disk, adjoining the event horizon, it would be seen the dark silhouette of the event horizon. Just the dark silhouette of the event horizon is seen on the first image of the supermassive**black****hole**M87* obtained by Event Horizon Telescope. The brightness of accretion matter near the**black****hole**highly exceeds the corresponding one of the usual astrophysical stationary background in the form of stars or gas clouds. For this reason, it is improbable to observe the**black****hole**shadow in the presence of a very luminous accretion matter.24 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Testing Horndeski Theory Using Light Deflection by Asymptotically Flat **Black** **Holes**

We also examine the graphical impact of deflection angle on asymptotically flat

**black****holes**in the background of Horndeski theory in plasma as well as non-plasma medium. Expand abstract.The principal objective of this project is to investigate the gravitational lensing by asymptotically flat

**black****holes**in the framework of Horndeski theory in weak field limits. To achieve this objective, we utilize the Gauss-Bonnet theorem to the optical geometry of asymptotically flat**black****holes**and applying the Gibbons-Werner technique to achieve the deflection angle of photons in weak field limits. Subsequently, we manifest the influence of plasma medium on deflection of photons by asymptotically flat**black****holes**in the context of Horndeski theory. We also examine the graphical impact of deflection angle on asymptotically flat**black****holes**in the background of Horndeski theory in plasma as well as non-plasma medium.25 days ago

10/10 relevant

Preprints.org

10/10 relevant

Preprints.org

Finite-Distance Gravitational Deflection of Massive Particles by the Kerr-like **Black** **Hole** in the Bumblebee Gravity Model

In this paper, we study the weak gravitational deflection angle of relativistic massive particles by the Kerr-like

**black****hole**in the bumblebee gravity model. Expand abstract.In this paper, we study the weak gravitational deflection angle of relativistic massive particles by the Kerr-like

**black****hole**in the bumblebee gravity model. In particular, we focus on weak field limits and calculate the deflection angle for a receiver and source at a finite distance from the lens. To this end, we use the Gauss-Bonnet theorem of a two-dimensional surface defined by a generalized Jacobi metric. The spacetime is asymptotically non-flat due to the existence of a bumblebee vector field. Thus the deflection angle is modified and can be divided into three parts: the surface integral of the Gaussian curvature, the path integral of a geodesic curvature of the particle ray and the change in the coordinate angle. In addition, we also obtain the same results by defining the deflection angle. The effects of the Lorentz breaking constant on the gravitational lensing are analyzed. We then consider the finite-distance correction for the deflection angle of massive particles.26 days ago

7/10 relevant

Preprints.org

7/10 relevant

Preprints.org

Modeling bias in supermassive **black** **hole** spin measurements

X-ray reflection spectroscopy (or iron line method) is a powerful tool to probe the strong gravity region of

**black****holes**, and currently is the only technique for measuring the spin of supermassive black**hole**s. Expand abstract. X-ray reflection spectroscopy (or iron line method) is a powerful tool to probe the strong gravity region of

**black**holes, and currently is the only technique for measuring the spin of supermassive**black****holes**. While all the available relativistic reflection models assume thin accretion disks, we know that several sources accrete near or above the Eddington limit and therefore must have thick accretion disks. In this Letter, we estimate the systematic error on the spin measurement when a source with a thick accretion disk is fitted with a thin disk model. Our results clearly show that the spin can be significantly overestimated. Current spin measurements of sources with high mass accretion rate are therefore not reliable.27 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Strong Cosmic Censorship for a Scalar Field in a Logarithmic-de Sitter
**Black** **Hole**

Relevant issues for Reissner-Nordstrom-de Sitter (RNdS)

**black****holes**and Born-Infeld-de Sitter (BI-dS) black**hole**s have been discussed. Expand abstract. It has been shown that the quasinormal modes of perturebated fields can be used to investigate the validity of strong cosmic censorship (SCC). Relevant issues for Reissner-Nordstrom-de Sitter (RNdS)

**black****holes**and Born-Infeld-de Sitter (BI-dS)**black****holes**have been discussed. In this paper, we investigate SCC in an asymptotic RN-dS**black****hole**with logarithmic nonlinear electromagnetic field perturbed by massless scalar fields. It has been argued that SCC can be violated in a near-extremal RN-dS**black****hole**. However, we find that the NLED effect can rescue SCC for a near-extremal logarithmic-de Sitter**black****hole**. Compared with Born-Infeld model, we find that the NLED effect have similar behavior.27 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Probing holography in $p$-adic CFT

We holographically calculate the partition functions of CFTs dual to Bruhat-Tits trees and $p$-adic BTZ black holes. Expand abstract.

We holographically calculate the partition functions of CFTs dual to Bruhat-Tits trees and $p$-adic BTZ

**black****holes**. Along the way, we propose new spectral decompositions of the Laplacian operator other than the plane-wave basis on these two types of backgrounds, with both analytical and numerical evidence. We extract the density of states and hence entropy from BTZ partition function via inverse Laplace transform. Then the one-loop Witten diagram is computed in the $p$-adic BTZ**black****hole**background, yielding constraints on the heavy-heavy-light averaged three-point coefficient of its boundary $p$-adic CFT. Finally, for general $p$-adic CFTs (not necessarily holographic), we analyze the representation theory of their global conformal group $PGL\left(2,\mathbb{Q}_p\right)$, and discuss the suitability of different representations as Hilbert spaces of $p$-adic CFT.28 days ago

6/10 relevant

arXiv

6/10 relevant

arXiv

Non-thermal aspects of Unruh effect

Although

**black****holes**are the best arena to explore this interplay, evidences for their existence are lacking, suggesting to address less exotic contexts. Expand abstract. The search for a relation among GR, QFT and TFT is the toughest challenge of theoretical physics since Hawking's discovery. The emergence of a temperature in spacetimes with an event horizon has unveiled the existence of a fertile territory, where gravity, thermal and quantum effects are non-trivially connected. Although

**black****holes**are the best arena to explore this interplay, evidences for their existence are lacking, suggesting to address less exotic contexts. In this sense, a promising stage is the QFT in curved space: specifically, the Unruh effect (UE) provides the first step toward unifying the quantum and gravity worlds via the EP. Waiting for a successful theory of quantum gravity, a careful investigation of UE, and, in particular, of any deviations of Unruh spectrum from its thermal behavior, may thus offer a window to new physics in the limbo between GR and QFT. Here we study the connection between geometric features of spacetime and ensuing thermal quantum phenomena from a non-traditional perspective, based on the analysis of perturbative effects that affect the standard scenarios. As a test bench, we consider the UE. After a discussion on the origin of UE, we examine to what extent its distinctive profile is spoilt i) for mixed neutrinos; ii) in presence of a minimal length arising from gravity at Planck scale. On one side, we show that the UE loses its thermality. Implications of this are analyzed in the context of the inverse beta-decay, also in view of the debate on a possible violation of the General Covariance of QFT. On the other, we focus on the effects induced by deformations of HUP, exploring the possibility to constrain the GUP-parameter via UE. The question is addressed of whether these unrelated frameworks have common roots. Along this line, we provide a unifying perspective of these effects, which still relies on a geometric interpretation of their origin.28 days ago

4/10 relevant

arXiv

4/10 relevant

arXiv

**Black** **holes**, Planckian granularity, and the changing cosmological
`constant'

In a recent work we have argued that nosy energy momentum diffusion due to space-time discreteness at the Planck scale (naturally expected to arise from quantum gravity) can be responsible for the generation of a cosmological constant during the electro-weak phase transition era of the cosmic evolution. Expand abstract.

In a recent work we have argued that nosy energy momentum diffusion due to space-time discreteness at the Planck scale (naturally expected to arise from quantum gravity) can be responsible for the generation of a cosmological constant during the electro-weak phase transition era of the cosmic evolution. Simple dimensional analysis and an effectively Brownian description of the propagation of fundamental particles on a granular background yields a cosmological constant of the order of magnitude of the observed value, without fine tuning. While the energy diffusion is negligible for matter in standard astrophysical configurations (from ordinary stars to neutron stars) here we argue that a similar diffusion mechanism could, nonetheless be important for

**black****holes**. If such effects are taken into account two observational puzzles might be solved by a single mechanism: the `$H_0$ tension' and the relatively low rotational spin of the**black****holes**detected via gravitational wave astronomy.28 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Unitarity from a smooth horizon?

Under semiclassical evolution,

**black****holes**retain a smooth horizon but fail to return information. Expand abstract. Under semiclassical evolution,

**black****holes**retain a smooth horizon but fail to return information. Yet, the Ryu-Takayanagi prescription computes the boundary entropy expected from unitary CFT evolution. We demonstrate this in a novel setting with an asymptotic bulk detector, eliminating an assumption about the entanglement wedge of auxiliary systems. We consider three interpretations of this result. (i) At face value, information is lost in the bulk but not in the CFT. This conflicts with the AdS/CFT dictionary. (ii) No unique QFT state (pure or mixed) governs all detector responses to the bulk Hawking radiation. This conflicts with the existence of an S-matrix. (iii) Nonlocal couplings to the**black****hole**interior cause asymptotic detectors to respond as though the radiation was pure, even though it is naively thermal. This invalidates the standard interpretation of the semiclassical state, including its smoothness at the horizon. We conclude that unitary boundary evolution requires asymptotic bulk detectors to become unambiguously pure at late times. We ask whether the RT prescription can still reproduce the boundary entropy in this bulk scenario. We find that this requires a substantial failure of semiclassical gravity in a low-curvature region, such as a firewall that purifies the Hawking radiation. Finally, we allow that the dual to semiclassical gravity may be an ensemble of unitary theories. This appears to relax the tensions we found: the ensemble average of out-states would be mixed, but the ensemble average of final entropies would vanish.28 days ago

7/10 relevant

arXiv

7/10 relevant

arXiv