Horizon acoustics of the GHS black hole and the spectrum of AdS2

We uncover a novel structure in Einstein-Maxwell-dilaton gravity: an AdS2 × S2 solution in string frame, which can be obtained by a near-horizon limit of the extreme GHS black hole with dilaton coupling λ ≠ 1. Unlike the Bertotti-Robinson spacetime, our solution has independent length scales for the AdS2 and S2, with ratio controlled by λ. We solve the perturbation problem for this solution, finding the independently propagating towers of states in terms of superpositions of gravitons, photons, and dilatons and their associated effective potentials. These potentials describe modes obeying conformal quantum mechanics, with couplings that we compute, and can be recast as giving the spectrum of the effective masses of the modes. By dictating the conformal weights of boundary operators, this spectrum provides crucial data for any future construction of a holographic dual to these AdS2 × S2 configurations.

New $$ \mathcal{N} $$ = (0, 4) AdS3 near-horizons in Type IIB

We construct new families of $$ \mathcal{N} $$ N = (0, 4) AdS3 × S2 × $$ {\tilde{S}}^2 $$ S ˜ 2 × S1 backgrounds fibred over a 2d Riemann surface in Type IIB string theory. These solutions are obtained by extracting the near-horizon limit of D3-brane box configurations, consisting of D3-D5-NS5 branes ending on D5′-NS5′ background branes. We relate our families of solutions to previous AdS3 × S2 × CY2 and AdS3 × S3 × S2 solutions to Type IIA recently constructed in the literature. We construct explicit 2d quiver CFTs associated to the D3-brane box configurations, and check that the central charges match the holographic result. We extend our solutions to include D7-branes, and show that a subclass of these solutions can be interpreted in terms of D3-D5-NS5 defect branes embedded in a 5d fixed point theory. This is explicitly realised by linking our solutions to a 6d domain wall that asymptotes locally the AdS6 × S2 × Σ2 solution T-dual to the Brandhuber-Oz vacuum.

Warped AdS2 and SU(1, 1|4) symmetry in Type IIB

We investigate the existence of solutions with 16 supersymmetries to Type IIB supergravity on a spacetime of the form AdS2× S5× S1 warped over a two-dimensional Riemann surface Σ. The existence of the Lie superalgebra SU(1, 1|4) ⊂ PSU(2, 2|4), whose maximal bosonic subalgebra is SO(1, 2)⊕SO(6)⊕SO(2), motivates the search for half-BPS solutions with this isometry that are asymptotic to AdS5×S5. We reduce the BPS equations to the Ansatz for the bosonic fields and supersymmetry generators compatible with these symmetries, then show that the only non-trivial solution is the maximally supersymmetric solution AdS5× S5. We argue that this implies that no solutions exist for fully back-reacted D7 probe or D7/D3 intersecting branes whose near-horizon limit is of the form AdS2× S5× S1× Σ.

From microscopic black hole entropy toward Hawking radiationc

The AdS/CFT correspondence has recently provided a novel approach for counting the microstates of black holes impressively matching the macroscopic Bekenstein–Hawking entropy formula of rotating electrically charged asymptotically AdS black holes in four to seven dimensions. This approach is designed for supersymmetric extremal black holes, but can also be extended to nonsupersymmetric, near-extremal black holes. Besides the dual higher-dimensional boundary CFT, an effective 2D CFT emerges in a certain near-horizon limit accounting for both the extremal and the near-extremal black hole entropies. This effective 2D description is universal across dimensions and comes naturally equipped with an approach to quantitatively tackle aspects of Hawking radiation.

Quantum Gravity Strategy for the Production of Dark Matter Using Cavitation by Minimum Entropy

The minimum entropy is responsible for the formation of dark matter bubbles in a black hole, while the variation in the density of dark matter allows these bubbles to leave the event horizon. Some experimental evidence supports the dark matter production model in the inner vicinity of the border of a black hole. The principle of minima entropy explains how cavitation occurs on the event horizon, which in turn complies with the Navier–Stokes 3D equations. Moreover, current works in an axiomatic way show that in the event horizon Einstein’s equations are equivalent to Navier–Stokes’ equations. Thus, The solutions of Einstein combined with the boundary conditions establish a one-to-one correspondence with solutions of incompressible Navier–Stokes and in the near-horizon limit it provides a precise mathematical sense in which horizons are always incompressible fluids. It is also essential to understand that Cavitation by minimum entropy is the production of dark matter bubbles, by variation of the pressure inside or on the horizon of a black hole, in general Δ p = p n + 1 − p n = σ n σ n + 1 − 1 p n or in particular Δ p = − ( 1 − P ) p 0 , where ∂ P ∂ t = Δ p ρ 0 P . Finally, fluctuations in the density of dark matter can facilitate its escape from a black hole, if and only if there is previously dark matter produced by cavitation inside or on the horizon of a black hole and also ρ D M < ρ B .

Implications of the search for optical counterparts during the first six months of the Advanced LIGO’s and Advanced Virgo’s third observing run: possible limits on the ejecta mass and binary properties

ABSTRACT GW170817 showed that neutron star mergers not only emit gravitational waves but also can release electromagnetic signatures in multiple wavelengths. Within the first half of the third observing run of the Advanced LIGO and Virgo detectors, there have been a number of gravitational wave candidates of compact binary systems for which at least one component is potentially a neutron star. In this article, we look at the candidates S190425z, S190426c, S190510g, S190901ap, and S190910h, predicted to have potentially a non-zero remnant mass, in more detail. All these triggers have been followed up with extensive campaigns by the astronomical community doing electromagnetic searches for their optical counterparts; however, according to the released classification, there is a high probability that some of these events might not be of extraterrestrial origin. Assuming that the triggers are caused by a compact binary coalescence and that the individual source locations have been covered during the EM follow-up campaigns, we employ three different kilonova models and apply them to derive possible constraints on the matter ejection consistent with the publicly available gravitational-wave trigger information and the lack of a kilonova detection. These upper bounds on the ejecta mass can be related to limits on the maximum mass of the binary neutron star candidate S190425z and to constraints on the mass-ratio, spin, and NS compactness for the potential black hole–neutron star candidate S190426c. Our results show that deeper electromagnetic observations for future gravitational wave events near the horizon limit of the advanced detectors are essential.

The primordial black hole formation criterion re-examined: Parametrisation, timing and the choice of window function

In this paper, the criterion used to determine whether a density perturbation will collapse to form a primordial black hole (PBH) is re-examined in respect of its use to determine the abundance of PBHs. There is particular focus on which parameter to use, the time at which the abundance should be calculated, and the use of different smoothing functions. It is concluded that, with the tools currently available, the smoothed density contrast should be used rather than the peak value, and should be calculated from the time-independent component of the density contrast in the super-horizon limit (long before perturbations enter the horizon) rather than at horizon crossing. For the first time, the effect of the choice of smoothing function upon the formation criterion is calculated, and, for a given abundance of PBHs, it is found that the uncertainty in the amplitude of the power spectrum due to this is [Formula: see text], an order of magnitude smaller than that suggested by previous calculations. The relation between the formation criterion stated in terms of the density contrast and the curvature perturbation [Formula: see text] is also discussed.

Holographic Aspects of Chaos and Integrability in String- and M-Theory

In this thesis we investigate classical integrability of the string worldsheet on different super-gravity backgrounds. We focus in particular on the class of half-supersymmetric AdS7 solutions of Massive Type IIA supergravity, that are thought to be the near-horizon limit of a D6-D8-NS5 Hanany-Witten brane set-up, and are dual to six-dimensional conformal field theories with N = (1, 0) supersymmetry. We use both analytical and numerical methods to show the (bosonic sector of the) string worldsheet is non-integrable on most of these backgrounds. The backgrounds on which the string is integrable are an infinite massless solution (corresponding to an infinite constant quiver), and a background corresponding to an infinite linear quiver theory.In addition we find that the (bosonic sector of the) string is integrable on a background that we call AdS7 × (S3)λ. For this background we show that it corresponds to a 6d SCFT with an infinitely long quiver with an infinite number of flavour groups, all proportional to the colour groups. We study this particular supergravity background in detail, and suggest it corresponds to the large-N limit of the dual SCFT in the limit where the Chern-Simons level k goes to infinity.This integrable AdS7 × (S3)λ background can be obtained as the λ-deformation of AdS7×S3. In this context we study integrable deformations of supergravity backgrounds in the last part of this thesis, in particular non-Abelian T-duality. We present another back-ground on which the string is integrable by performing two non-Abelian T-dualities on two three-spheres inside the AdS5×S5 solution and study the resulting background.

Schwinger effect in an instanton background with electric and magnetic fields via holography

The Schwinger effect in the presence of instantons and background magnetic field was considered to study the dependence of critical electric field on instanton density and magnetic field using AdS/CFT conjecture. The gravity side is the near horizon limit of D3[Formula: see text]D(−[Formula: see text]1) background with electric and magnetic fields on the brane. Our approach is based on the potential analysis for particle–antiparticle pair at zero and finite temperatures, where the zero temperature case is a semi-confining theory. We find that presence of instantons suppresses the pair creation effect, similar to a background magnetic field. Then, the production rate will be obtained numerically using the expectation value of circular Wilson loop. The obtained production rate in a magnetic field is in agreement with previous results.