arXiv subjects

Prieslei Goulart

Publications and source records attributed to Prieslei Goulart.

8 recordsLinked to original sources

arXiv2019

S-duality, entropy function and transport in $AdS_4/CMT_3$

In this paper we consider Abelian vector plus scalar holographic gravity models for 2+1 dimensional condensed matter transport, and the effect of S-duality on them. We find the transport coefficients from the electric and heat currents via usual membrane paradigm-type calculations, and the effect of S-duality on them. We study the same system also by using the entropy function formalism in the extremal case, and the formalism of holographic Stokes equations, in the case of one-dimensional lattices. We study a few generalizations that appear when considering a supergravity-inspired model, and apply the entropy function method for them.

hep-th↗

arXiv2018

Violation of Weak Cosmic Censorship in Einstein-Maxwell-dilaton theory: singularities connected by traversable wormholes

We give two new analytical solutions to the low-energy string theory action that violate the weak cosmic censorship conjecture. They are classical charged solutions to the Einstein-Maxwell-dilaton theory in four dimensions that come in two types. The first represents one single naked singularity whose asymptotic region is flat. Its mass respects the positive mass theorem. The absence of horizons allows us to probe quantum aspects of gravity by direct observation of these singularities. The second represents singularities that come in pairs that "seem to create their own spacetime", and the region connecting them has the geometry of a traversable wormhole. In other words, they represent a pair of singularities connected by a traversable wormhole. The dyonic solution has a limit free of singularities, which we call "extremal limit" in analogy with black holes. This has a geometry given by the AdS$_{2}\times$S$^{2}$ spacetime in global coordinates. We compute the physical charges for the naked singularities and show that the weak gravity conjecture can be respected or violated, depending on the parameters of the solutions. We also compute the light deflection angle.

gr-qc↗

arXiv2017

Phantom wormholes in Einstein-Maxwell-dilaton theory

In this paper we give an electrically charged traversable wormhole solution for the Einstein-Maxwell-dilaton theory when the dilaton is a phantom field, i.e. it has flipped sign kinetic term appearing in the action. In the limit when the charge is zero, we recover the anti-Fisher solution, which can be reduced to the Bronnikov-Ellis solution under certain choices of integration constants. The equations of motion of this theory share the same S-duality invariance of string theory, so the electrically charged solution is rotated into the magnetically charged one by applying such transformations. The scalar field is topological, so we compute its topological charge, and discuss that under appropriate boundary conditions we can have a lump, a kink, or an anti-kink profile. We determine the position of the throat, and show the embedding diagram of the wormhole. As a physical application, we apply the Gauss-Bonnet theorem to compute the deflection angle of a light-ray that passes close to the wormhole.

gr-qc↗

arXiv2017

Dyonic black holes and dilaton charge in string theory

We present the four-dimensional non-extremal dyonic black hole solution for Einstein-Maxwell-dilaton theory in absence of a scalar potential written in terms of integration constants only. These integration constants must satisfy a set of conditions imposed by the equations of motion. By defining a posteriori the mass $M$ of the black hole and the dilaton charge $Σ$, we show how to recover the dyonic black hole solution found by Kallosh et.al. In particular, our analysis show that there is a possibility in defining whether the dilaton charge or the mass of the black hole is an independent parameter. When the mass of the black hole is the independent parameter, then there is a well-defined limit in which the dilaton charge is zero. For this case, it is straightforward to provide an answer to why is $ϕ_{H, \text{extreme}}$ independent of $ϕ_{0}$ and to why $ϕ_{H, \text{extreme}}=ϕ_{0}$ when the dilaton charge is zero.

hep-th↗

arXiv2017

Massless black holes and charged wormholes in string theory

We discuss the zero mass pointlike solutions and charged Einstein-Rosen bridges (wormholes) that arise from the dyonic black hole solution of the Einstein-Maxwell-dilaton theory. These massless black holes exist individually in spacetime, different from the known massless solutions, which come in pairs with opposite signs for their masses. In order to construct a massless object, we choose the integration constants of the solution to have specific values. The massless solutions present some problems: in one case the dilaton field is complex (or the gauge field has negative kinetic energy), and in the other case the solution has negative entropy and temperature or it is naked singularity in the extremal limit. For the first case, the observables computed are real quantities. This massless solution also allow the bridge construction, and we obtain an analytical and static charged wormhole solution, which satisfies the null energy condition.

hep-th↗

arXiv2017

Conductivities from attractors

In the context of applications of the AdS/CFT correspondence to condensed matter physics, we compute conductivities for field theory duals of dyonic planar black holes in 3+1-dimensional Einstein-Maxwell-dilaton theories at zero temperature. We combine the near-horizon data obtained via Sen's entropy function formalism with known expressions for conductivities. In this way we express the conductivities in terms of the extremal black hole charges. We apply our approach to three different examples for dilaton theories for which the background geometry is not known explicitly. For a constant scalar potential, the thermoelectric conductivity explicitly scales as $α_{xy}\sim N^{3/2}$, as expected. For the same model, our approach yields a finite result for the heat conductivity $κ/T \propto N^{3/2}$ even for $T \rightarrow 0$.

hep-th↗

arXiv2016

Dyonic AdS_4 black hole entropy and attractors via entropy function

Using the Sen's entropy function formalism, we compute the entropy for the extremal dyonic black hole solutions of theories in the presence of dilaton field coupled to the field strength and a dilaton potential. We solve the attractor equations analytically and determine the near horizon metric, the value of the scalar fields and the electric field on the horizon, and consequently the entropy of these black holes. The attractor mechanism plays a very important role for these systems, and after studying the simplest systems involving dilaton fields, we propose a general ansatz for the value of the scalar field on the horizon, which allows us to solve the attractor equations for gauged supergravity theories in $AdS_4$ spaces. In particular, we derive an expression for the dyonic black hole entropy for the $\mathcal{N}=8$ gauged supergravity in 4 dimensions which does not contain explicitly the gauge parameter of the potential.

hep-th↗

arXiv2015

Massive ABJM and black hole entropy in the presence of field strength coupling to curvature

Assuming that the near horizon geometry of the black hole solution of the gravity dual to the ABJM model, in the presence of a coupling between the Weyl tensor and the field strength, is $AdS_{2}\times S^{2}$, we compute Sen's entropy function for this theory. By extremizing the entropy function we write a formula for the entropy of the black hole, and then we compute the same entropy using Wald's formula and show that the results are the same. In this way we generalize the calculation of black hole entropy to cases of curvature coupling to the field strength, including at first order, and we also show how to calculate the black hole entropy when the black hole solution is unknown, from just a few simple assumptions about the horizon.

hep-th↗