Antisymmetric-Tensor and Electromagnetic effects in an alpha'-non-perturbative Four-Dimensional String Cosmology

TL;DR

This paper explores non-perturbative four-dimensional string cosmology solutions involving antisymmetric tensor fields, revealing their impact on universe anisotropies and optical activity, with potential cosmological implications.

Contribution

It introduces an alpha'-non-perturbative approach to string cosmology, analyzing antisymmetric tensor effects beyond perturbation theory in a four-dimensional setting.

Findings

Antisymmetric tensor induces spatial anisotropies in the universe.

Coupling to electromagnetic fields causes optical activity.

Estimates suggest relevance to current cosmological observations.

Abstract

Starting from an exact (in the Regge slope alpha') functional method for a bosonic stringy sigma-model, we investigate four-dimensional cosmological string solutions in graviton, dilaton and antisymmetric tensor backgrounds, compatible with world-sheet conformal invariance, and valid beyond perturbative expansions in powers of alpha'. The antisymmetric tensor field, playing the role of an axion in the four-dimensional target space time, leads to spatial anisotropies of the emergent Robertson-Walker expanding Universe, and, upon coupling the system to the electromagnetic field, it results in non-trivial optical activity. Some estimates of the corresponding effects are made and their relevance to current cosmology is briefly discussed.