Non-perturbative time-dependent String Backgrounds and Axion-induced Optical Activity

TL;DR

This paper develops a non-perturbative approach to time-dependent string backgrounds, demonstrating how axion-induced optical activity could serve as an observable signature of string-inspired effects in a four-dimensional universe.

Contribution

It introduces a method to achieve conformal invariance in time-dependent string backgrounds to all orders in alpha prime, and explores electromagnetic effects of the antisymmetric tensor field in a cosmological setting.

Findings

Non-trivial optical activity due to axion/dilaton effects

Conformal invariance achieved in any target space dimension

Potential observational signatures in a Minkowski universe

Abstract

Conformal invariance for bosonic strings in time-dependent backgrounds of graviton, dilaton and Kalb-Ramond field is obtained by imposing Weyl-beta functions to be homogeneous in time, to all orders in $\alpha^{'}$. This construction is possible in any target space dimension, as a result of the non-trivial background configurations. The electromagnetic effects of the antisymmetric tensor field, when coupled to an Abelian (electromagnetic) gauge field, are discussed in the framework of a four-dimensional Minkowski Universe, for concreteness. Non-trivial optical activity is demonstrated, which constitutes a way of detecting string-inspired axion/dilaton effects in such models.