SearcharxivSearch

arXiv subjects

W. Barreto

Publications and source records attributed to W. Barreto.

At least 19 recordsLinked to original sources

Iso-$\mu/T$ holographic entropy and its attractor for a strongly coupled quantum fluid

Numerical evidence has shown that a period of vanishing entropy production during far-from-equilibrium stages induces subsequent violations of the dominant energy condition in strongly coupled plasmas. This behavior also appears to hold for a Bjorken-expanding, hot and dense strongly coupled quantum fluid. In this context, it has been established that the chemical potential-to-temperature ratio ($\mu/T$) in the medium increases with higher initial charge density, $\rho_0$, and/or lower initial energy density, $\varepsilon_0$. Here, we present a numerical method to evolve Bjorken R-charged plasmas by varying $(\varepsilon_0,\rho_0)$ in order to generate a curve that preserves a constant $\mu/T$. This allows us to address the case in which all Bekenstein-Hawking entropy densities evolve towards configurations with the same $\mu/T$. This approach enables a more direct comparison with the $\mathcal{N}=4$ SYM plasma case ($\mu/T=0$) and, consequently, provides clearer evidence of the correlation between entropy production and violations of the dominant energy condition. Moreover, this procedure offers a characterization (albeit numerical and partial) of the iso$-\mu/T$ entropy density hydrodynamic attractor for hot and dense strongly coupled quantum fluids.

hep-th

Extracting more information from entropy

We extract the complex frequency of the lowest quasi-normal mode from the holographically computed entropy density near thermodynamic equilibrium. The system consists of a purely thermal Supersymmetric Yang-Mills N=4 plasma in homogeneous isotropization dynamics. The initial state is far-from-equilibrium, proceeding to thermalization over time. The system evolves to equilibrium entropy forming a stairway pattern. The analysis reveals that the rate of increase of the stairway is twice the decay rate of the lowest quasi-normal mode. This leads us to propose a model explaining how this information is encoded in entropy. The model is extended to consider finite temperature, R-charge density and scalar condensate of the medium, disclosing an additional feature. The system's main dissipation channel may shift to one driven by the scalar condensate, depending on the chemical potential.

hep-th

Configurational entropy of generalized sine-Gordon-type models

A family of deformed models of the sine-Gordon-type can be generated by twisting the sine-Gordon model. As a particular case, the 3-sine-Gordon model is here addressed, whose differential configurational entropy and the differential configurational complexity of three topological sectors are discussed, using two complementary approaches. Stability aspects are also discussed.

hep-th

Configurational entropy of black hole quantum cores

Two types of information entropy are studied for the quantum states of a model for the matter core inside a black hole geometry. A detailed description is first given of the quantum mechanical picture leading to a spectrum of bound states for a collapsing ball of dust in general relativity with a non-trivial ground state. Information entropies are then computed, shedding new light on the stability of the ground state and the spectrum of higher excited states.

gr-qc

Gravitational collapse in AdS: instabilities, turbulence, and information

The gravitational collapse in asymptotically AdS spacetimes is studied, using the differential configurational entropy (DCE). The DCE is shown to comply with the instability of the Einstein-Klein-Gordon system, leading to different stages in the route to turbulence and final black hole formation, including near the critical behavior.

hep-th

Differential configurational entropy and the gravitational collapse of a kink

The gravitational instability of kinks is scrutinized in the context of information entropy, including the black hole formation near the scalar field critical collapse. The differential configurational entropy (DCE) is computed and examined for globally perturbed static kinks and the far-from-equilibrium kink solutions as well. In the case of the first kink, the DCE determines a critical value of the perturbation parameter regulating points of bifurcation that characterize a phase transition, whose supercritical range leads to collapse and subsequent black hole formation. For the far-from-equilibrium kink solutions, the DCE supports black hole formation.

hep-th

Rio: A new computational framework for accurate initial data of binary black holes

We present a computational framework (Rio) in the ADM 3+1 approach for numerical relativity. This work enables us to carry out high resolution calculations for initial data of two arbitrary black holes. We use the transverse conformal treatment, the Bowen-York and the puncture methods. For the numerical solution of the Hamiltonian constraint we use the domain decomposition and the spectral decomposition of Galerkin-Collocation. The nonlinear numerical code solves the set of equations for the spectral modes using the standard Newton-Raphson method, LU decomposition and Gaussian quadratures. We show the convergence of the Rio code. This code allows for easy deployment of large calculations. We show how the spin of one of the black holes is manifest in the conformal factor.

gr-qc

Galerkin-Collocation domain decomposition method for arbitrary binary black holes

We present a new computational framework for the Galerkin-collocation method for double domain in the context of ADM 3+1 approach in numerical relativity. This work enables us to perform high resolution calculations for initial sets of two arbitrary black holes. We use the Bowen-York method for binary systems and the puncture method to solve the Hamiltonian constraint. The nonlinear numerical code solves the set of equations for the spectral modes using the standard Newton-Raphson method, LU decomposition and Gaussian quadratures. We show convergence of our code for the conformal factor and the ADM mass. Thus, we display features of the conformal factor for different masses, spins and linear momenta.

gr-qc

Fixed mesh refinement in the characteristic formulation of General Relativity

We implement a spatially fixed mesh refinement under spherical symmetry for the characteristic formulation of General Relativity. The Courant-Friedrich-Levy (CFL) condition lets us deploy an adaptive resolution in (retarded-like) time, even for the nonlinear regime. As test cases, we replicate the main features of the gravitational critical behavior and the spacetime structure at null infinity using the Bondi mass and the News function. Additionally, we obtain the global energy conservation for an extreme situation, i.e. in the threshold of the black hole formation. In principle, the calibrated code can be used in conjunction with an ADM 3+1 code to confirm the critical behavior recently reported in the gravitational collapse of a massless scalar field in an asymptotic anti-de Sitter spacetime. For the scenarios studied, the fixed mesh refinement offers improved runtime and results comparable to code without mesh refinement.

gr-qc

Nonlinear interaction between electromagnetic and gravitational waves: an appraisal

Wave propagation of field disturbances is ubiquitous. The electromagnetic and gravitational are cousin theories in which the corresponding waves play a relevant role to understand several related physical. It has been established that small electromagnetic waves can generate gravitational waves and vice versa when scattered by a charged black hole. In the realm of cylindrical spacetimes, we present here a simple nonlinear effect of the conversion of electromagnetic to gravitational waves reflected by the amount of mass extracted from them.

gr-qc

A (gravitational) toy story

Frequently in Physics, insights and conclusions can be drawn from simple, idealized models. The discovery of critical behavior in the gravitational collapse of a massless scalar field leads to the simulation of binary black holes, from its coalescence to merging and ringdown. We refined a toy model to explore black hole formation as these events unfold to revisit the instability of a gravitational kink. We confirmed a conjecture related to a mass gap, for critical behavior at the threshold of black hole formation. We find a critical exponent twice the standard value. Surprisingly, this larger critical exponent is also present in the multiple critical behavior for the black hole formation from a massless scalar field in asymptotically anti-de Sitter spacetimes. What is the meaning of this mass gap? Does it have physical relevance?

gr-qc

Mass gap in the critical gravitational collapse of a kink

We study the gravitational collapse of a kink within spherical symmetry and the characteristic formulation of General Relativity. We explore some expected but elusive gravitational collapse issues which have not been studied before in detail, finding new features. The numerical one-parametric solution and the structure of the spacetime are calculated using finite differences, Galerkin collocation techniques, and some scripting for automated grid coverage. We study the threshold of black hole formation and confirm a mass gap in the phase transition. In the supercritical case we find a mass scaling power law $M_{BH}={M^*_{BH}}+K[λ-λ^*]^{2γ}+f(K[λ-λ^*]^{2γ})$, with $γ\approx 0.37$ independent of the initial data for the cases considered, and $M^*_{BH}$, $K$ and $λ^*$ each depending on the initial datum. The spacetime has a self-similar structure with a period of $Δ\approx 3.4$. In the subcritical case the Bondi mass at null infinity decays in cascade with $Δ/2$ interval as expected.

gr-qc

Conformally flat polytropes for anisotropic matter

We analyze in detail conformally flat spherically symmetric fluid distributions, satisfying a polytropic equation of state. Among the two possible families of relativistic polytropes, only one contains models which satisfy all the required physical conditions. The ensuing configurations are necessarily anisotropic and show interesting physical properties. Prospective applications of the presented models to the study of super-Chandrasekhar white dwarfs, are discussed.

gr-qc

Extended two-dimensional characteristic framework to study nonrotating black holes

We develop a numerical solver, that extends the computational framework considered in [Phys. Rev. D 65, 084016 (2002)], to include scalar perturbations of nonrotating black holes. The nonlinear Einstein-Klein-Gordon equations for a massless scalar field minimally coupled to gravity are solved in two spatial dimensions (2D). The numerical procedure is based on the ingoing light cone formulation for an axially and reflection symmetric spacetime. The solver is second order accurate and was validated in different ways. We use for calibration an auxiliary 1D solver with the same initial and boundary conditions and the same evolution algorithm. We reproduce the quasinormal modes for the massless scalar field harmonics $\ell = 0$, $1$ and $2$. For these same harmonics, in the linear approximation, we calculate the balance of energy between the black hole and the world tube. As an example of nonlinear harmonic generation, we show the distortion of a marginally trapped two-surface approximated as a q-boundary and based upon the harmonic $\ell=2$. Additionally, we study the evolution of the $\ell = 8$ harmonic in order to test the solver in a spacetime with a complex angular structure. Further applications and extensions are briefly discussed.

gr-qc

Global energy conservation in nonlinear spherical characteristic evolutions

Associated to the unique 4-parametric subgroup of translations, normal to the Bondi-Metzner-Sachs group, there exists a generator of the temporal translation asymptotic symmetry. Such a descriptor of the motion along the conformal orbit near null infinity is propagated to finite regions. This allows us to observe the global energy conservation even in extreme situations near the critical behavior of the massless scalar field collapse in spherical symmetry.

gr-qc

General relativistic polytropes for anisotropic matter: The general formalism and applications

We set up in detail the general formalism to model polytropic general relativistic stars with anisotropic pressure. We shall consider two different possible polytropic equations, all of which yield the same Lane-Emden equation in the Newtonian limit. A heuristic model based on an ansatz to obtain anisotropic matter solutions from known solutions for isotropic matter is adopted to illustrate the effects of the pressure anisotropy on the structure of the star. In this context, the Tolman mass, which is a measure of the active gravitational mass, is invoked to explain some features of the models. Prospective extensions of the proposed approach are pointed out.

gr-qc

An evolution of adiabatic matter: A case for the quasistatic regime

We establish the connection between the standard ADM 3+1 treatment of matter with its characteristic equivalent, in the context of spherical symmetry. The flux-conservative rendition of the fluid equations are obtained. Considering adiabatic distributions of perfect fluid, we evolve the system using the so-called post-quasi-static approximation in radiation coordinates. We obtain an adiabatic matter evolution in the quasi-static regime or slow motion, which is not shear-free nor geodesic.

gr-qc

Newtonian polytropes for anisotropic matter: General framework and applications

We set up the general formalism to model polytropic Newtonian stars with anisotropic pressure. We obtain the corresponding Lane-Emden equation. A heuristic model based on an ansatz to obtain anisotropic matter solutions from known solutions for isotropic matter is adopted to illustrate the effects of the pressure anisotropy on the structure of the star. In particular, we calculate the Chandrasekhar mass for a white dwarf. It is clearly displayed how the Chandrasekhar mass limit changes depending on the anisotropy. Prospective astrophysical applications of the proposed approach are discussed.

astro-ph.IM