Magneto-dilatonic Bianchi-I cosmology: isotropization and singularity problems

Abstract

We study the evolution of Bianchi-I space-times filled with a global unidirectional electromagnetic field Fµν interacting with a massless scalar dilatonic field according to the law Ψ(φ)F µν Fµν where Ψ(φ) > 0 is an arbitrary function. A qualitative study, among other results, shows that (i) the volume factor always evolves monotonically, (ii) there exist models becoming isotropic at late times and (iii) the expansion generically starts from a singularity but there can be special models starting from a Killing horizon preceded by a static stage. All three features are confirmed for exact solutions found for the usually considered case Ψ = e 2λφ , λ = const . In particular, isotropizing models are found for |λ| > 1/ √ 3 . In the special case |λ| = 1 , which corresponds to models of string origin, the string metric behaviour is studied and shown to be qualitatively similar to that of the Einstein frame metric.

On a Regular Charged black Hole with a Nonlinear Electric Source

“…To avoid the black hole (BH) singularity problem, a lot of regular models have been proposed [1,2,3,4,5,6,7,8,9,10,11]. Bardeen [1] was the first author presenting a regular BH model.…”

Nonlinear electromagnetic quasinormal modes and Hawking radiation of a regular black hole with magnetic charge

“…However, we also notice that there are some deficiencies of this metric. For instance the Lagrangian L(F) is not a monotonic function in the whole range of invariant F, but rather has some junctions where singularities appear [61][62][63]. This can be well shown using the effective metric [64].…”

Bianchi I in scalar and scalar-tensor cosmologies

“…(6 and 12-13) while the conservation equations are given by Eqs. (26)(27). As in the above studied cases the behaviour of the quantities is given by Eq.…”