Nora Bretón

BORN–INFELD COSMOLOGIES

We present a model for an inhomogeneous and anisotropic early universe filled with a nonlinear electromagnetic field of Born–Infeld (BI) type. The effects of the BI field are compared with the linear case (Maxwell). Since the curvature invariants are well behaved then we conjecture that our model does not present an initial big bang singularity. The existence of the BI field modifies the curvature invariants at t=0 as well as sets bounds on the amplitude of the conformal metric function.

Smarr's formula for black holes with non-linear electrodynamics

It is known that for nonlinear electrodynamics the First Law of Black Hole Mechanics holds, however the Smarr’s formula for the total mass does not. In this contribution we discuss the point and determine the corresponding expressions for the Bardeen black hole solution that represents a nonlinear magnetic monopole. The same is done for the regular black hole solution derived by Ayón–Beato and García [1], showing that in the case that variations of the electric charge are involved, the Smarr’s formula is no longer valid.

Geodesic structure of the Born-Infeld black hole

In this paper we study the trajectories of test particles in a geometry that is the nonlinear electromagnetic generalization of the Reissner–Nordstrom black hole. The solution was originally derived by Garcia, Salazar and Plebanski (1984 Nuovo Cimento 84 65–90). The studied spacetime is an Einstein–Born–Infeld solution, nonsingular outside a regular event horizon and characterized by three parameters: mass M, charge Q and the Born–Infeld parameter b related to the magnitude of the electric field at the origin. Asymptotically it is a Reissner–Nordstrom solution.

Stability of nonlinear magnetic black holes

We study the stability of static spherically symmetric exact solutions of Einstein equations coupled with nonlinear electrodynamics, in the magnetic sector. These solutions satisfy the heuristic model proposed by Ashtekar, Corichi, and Sudarsky for hairy black holes, meaning that the horizon mass is related to their Arnowitt-Deser-Misner (ADM) mass and to the corresponding particlelike solution. We test the unstability conjecture that emerges for hairy black holes and it turned out that it becomes confirmed except for the Einstein-Born-Infeld solutions.

Singularity-free Bianchi spaces with nonlinear electrodynamics

In this paper we present an analysis to determine the existence of singularities in spatially homogeneous anisotropic universes filled with nonlinear electromagnetic radiation. These spaces are conformal to Bianchi spaces admitting a three parameter group of motions G3. For these models we study geodesic completeness. It is shown that with nonlinear electromagnetic field some of the Bianchi spaces are geodesically complete (G3VIII). The analysis of the Raychaudhuri equation reveals that the BI field is responsible for the absence of singularity. When certain topology is assumed, Bianchi G3IX may present geodesics that are imprisoned. In the linear limit (Maxwell field) the spacetimes are singular and they do not admit a cosmological interpretation in all the range of the time coordinate.

Nonlinear electrodynamics in Bianchi spacetimes

We study the effects produced by nonlinear electrodynamics in spacetimes conformal to Bianchi metrics. In the presence of Born–Infeld-type fields these models accelerate, expand and isotropize. This effect is compared with that corresponding to a linear electromagnetic field; it turns out that for the same geometry, a Maxwell field does not favour inflation as much as a Born–Infeld field. The behaviour of the nonlinear radiation is analysed in terms of the equations of state. The energy conditions are analysed as well, showing that the Born–Infeld field violates the strong energy condition.

Probing bulk viscous matter-dominated models with Gamma-ray bursts

In this paper we extend the range of consistency of a constant bulk viscosity model to redshifts up to

The Early Universe and Observational Cosmology

z\sim 8.1

Observational constraints on electromagnetic Born-Infeld cosmology

. In this model the dark sector of the cosmic substratum is a viscous fluid with pressure

The Bel-Robinson tensor for the collision of gravitational plane waves

p= -\zeta \theta