Anisotropic `hairs' in string cosmology

Anisotropic ’hairs’ in string cosmology

In most models, inflation is driven by the potential energy of a scalar field. This has similar effects as adding vacuum energy or, equivalently, a positive cosmological constant. For these models Wald [1] proved a cosmic no hair theorem, which implies that an initial shear is inflated away [2]. A couple of years ago, a new mechanism of inflation has been proposed, where inflation is due to the...

Low - energy graceful exit in anisotropic string cosmology backgrounds

We discuss the possibility of a smooth transition from the preto the post-big bang regime, in the context of the lowest-order string effective action (without higher-derivative corrections), taking into account with a phenomenological model of source the repulsive gravitational effects due to the back-reaction of the quantum fluctuations outside the horizon. We determine a set of necessary cond...

Low-energy Graceful Exit in Anisotropic String Cosmology Backgrounds

We discuss the possibility of a smooth transition from the pre-to the post-big bang regime, in the context of the lowest-order string eeective action (without higher-derivative corrections), taking into account with a phenomenological model of source the repulsive gravitational eeects due to the back-reaction of the quantum uctuations outside the horizon. We determine a set of necessary conditi...

Anisotropic four-dimensional Neveu-Schwarz–Neveu-Schwarz string cosmology

An anisotropic ~Bianchi type I! cosmology is considered in the four-dimensional Neveu-Schwarz–NeveuSchwarz ~NS–NS! sector of low-energy effective string theory coupled to a dilaton and an axionlike H field within a de Sitter–Einstein frame background. The general solution of the gravitational field equations can be expressed in an exact parametric form in both Einstein and string frames. The st...

String Cosmology