arXiv subjects

M. Bouhmadi-Lopez

Publications and source records attributed to M. Bouhmadi-Lopez.

5 recordsLinked to original sources

arXiv2002

Topological defect brane-world models

5-dimensional homogeneous and isotropic models with a bulk cosmological constant and a minimally coupled scalar field are considered. We have found that in special cases the scalar field can mimic a frustrated (i.e. disordered) networks of topological defects: cosmic strings, domain walls and hyperdomain walls. This equivalence enabled us to obtain 5-dimensional instantonic solutions which can be used to construct brane-world models. In some cases, their analytic continuation to a Lorentzian metric signature give rise to either 4-dimensional flat or inflating branes. Models with arbitrary dimensions (D $>$ 5) are also briefly discussed.

hep-th↗

arXiv2002

On new gravitational instantons describing creation of brane-worlds

By considering 5--dimensional cosmological models with a bulk filled with a pressureless scalar field; equivalently dust matter, and a negative cosmological constant, we have found a regular instantonic solution which is free from any singularity at the origin of the extra--coordinate. This instanton describes 5--dimensional asymptotically anti de Sitter wormhole, when the bulk has a topology R times S^4. Compactified brane-world instantons which are built up from such instantonic solution describe either a single brane or a string of branes. Their analytical continuation to the pseudo--Riemannian metric can give rise to either 4-dimensional inflating branes or solutions with the same dynamical behaviour for extra--dimension and branes, in addition to multitemporal solutions. Dust brane-world models with arbitrary dimensions (D >= 5) as well as other spatial topologies are also briefly discussed.

hep-th↗

arXiv2002

Quantum behavior of FRW radiation-filled universes

We study the quantum vacuum fluctuations around closed Friedmann-Robertson-Walker (FRW) radiation-filled universes with nonvanishing cosmological constant. These vacuum fluctuations are represented by a conformally coupled massive scalar field and are treated in the lowest order of perturbation theory. In the semiclassical approximation, the perturbations are governed by differential equations which, properly linearized, become generalized Lame equations. The wave function thus obtained must satisfy appropriate regularity conditions which ensure its finiteness for every field configuration. We apply these results to asymptotically anti de-Sitter Euclidean wormhole spacetimes and show that there is no catastrophic particle creation in the Euclidean region, which would lead to divergences of the wave function.

gr-qc↗

arXiv2001

Perfect fluid brane-world model

By considering 5--dimensional cosmological models with a bulk filled with a perfect fluid and a cosmological constant, we have found regular instantonic solution which is free from any singularity at the origin of the extra--coordinate and describe 5--dimensional asymptotically anti de Sitter wormhole, when the bulk has a topology $ R \times S^4 $ and is filled with dust and a negative cosmological constant. Compactified brane-world instantons which are built up from such instantonic solution describe either a single brane or a string of branes. Their analytical continuation to the pseudo--Riemannian metric can give rise to either 4-dimensional inflating branes or solutions with the same dynamical behaviour for extra--dimension and branes, in addition to multitemporal solutions. Dust brane-world models with other spatial topologies are also considered.

hep-th↗

arXiv2001

Comments on conformal stability of brane-world models

The stability of 5-D brane-world models under conformal perturbations is investigated. The analysis is carried out in the general case and then it is applied to particular solutions. It is shown that models with the Poincare and the de Sitter branes are unstable because they have negative mass squared of gravexcitons whereas models with the Anti de Sitter branes have positive gravexciton mass squared and are stable. It is also shown that 4-D effective cosmological and gravitational constants on branes as well as gravexciton masses undergo hierarchy: they have different values on different branes.

hep-th↗