arXiv subjects

Darío Núñez

Publications and source records attributed to Darío Núñez.

42 records · Page 3Linked to original sources

arXiv2005

Constraint and gauge shocks in one-dimensional numerical relativity

We study how different types of blow-ups can occur in systems of hyperbolic evolution equations of the type found in general relativity. In particular, we discuss two independent criteria that can be used to determine when such blow-ups can be expected. One criteria is related with the so-called geometric blow-up leading to gradient catastrophes, while the other is based upon the ODE-mechanism leading to blow-ups within finite time. We show how both mechanisms work in the case of a simple one-dimensional wave equation with a dynamic wave speed and sources, and later explore how those blow-ups can appear in one-dimensional numerical relativity. In the latter case we recover the well known ``gauge shocks'' associated with Bona-Masso type slicing conditions. However, a crucial result of this study has been the identification of a second family of blow-ups associated with the way in which the constraints have been used to construct a hyperbolic formulation. We call these blow-ups ``constraint shocks'' and show that they are formulation specific, and that choices can be made to eliminate them or at least make them less severe.

gr-qc↗

arXiv2004

A natural mechanism to induce an electric charge into a black hole

We present a natural mechanism which may induce an electric charge into an accretting black hole in the presence of a strong, high energy radiation field. We study this mechanism using Newtonian physics, and we also discuss the process within the context of a Kerr Newman black hole. Finally, we consider possible astrophysical applications in X-ray variability and jet formation in the Active Galactic Nuclei (AGN).

astro-ph↗

arXiv1996

Black holes have no short hair

We show that in all theories in which black hole hair has been discovered, the region with non-trivial structure of the non-linear matter fields must extend beyond 3/2 the horizon radius, independently of all other parameters present in the theory. We argue that this is a universal lower bound that applies in every theory where hair is present. This {\it no short hair conjecture} is then put forward as a more modest alternative to the original {\it no hair conjecture}, the validity of which now seems doubtful.

gr-qc↗

arXiv1995

Class of Einstein--Maxwell Dilatons

Three different classes of static solutions of the Einstein--Maxwell equations non--minimally coupled to a dilaton field are presented. The solutions are given in general in terms of two arbitrary harmonic functions and involve among others an arbitrary parameter which determines their applicability as charged black holes, dilaton black holes or strings. Most of the known solutions are contained as special cases and can be non--trivially generalized in different ways.

gr-qc↗

arXiv1995

How short can the hair of a black hole be?

We show that in all theories in which black hole hair has been discovered, the region with non-trivial structure of the non-linear matter fields must extend beyond $3/ 2$ the horizon radius, independently of all other parameters present in the theory. We argue that this is a universal lower bound that applies in every theory where hair is present. This {\it no short hair conjecture} is then put forward as a more modest alternative to the now debunked {\it no hair conjecture}.

gr-qc↗

arXiv1995

Comment on "Quantum bound states with zero binding energy"

The purpose of this Comment is to show that the solutions to the zero energy Schrödinger equations for monomial central potentials discussed in a recently published Letter, may also be obtained from the corresponding free particle solutions in a straight forwardly way, using an algorithm previously devised by us. New solutions to the zero energy Schrödinger equation are also exhibited.

gr-qc↗