Tilt of COBE can constrain aspects of superstring geometry

Abstract

Superstring theories for which experimental evidence is meagre are considered a most promising approach to understand the quantum nature of gravity and its unification with other fundamental interactions. The geometric structure of these theories goes beyond the usual Riemannian one of general relativity. In the low energy limit they are well known not to simply reduce Einstein’s theory, but inevitably contain an antisymmetric field associated with space time torsion and a dilation scalar field. Although equivalence principle tests and evidence from the binary pulsar would make their effects very small these fields could have dominated in the inflationary epoch and left their imprints in the COBE spectrum. This approach enables us to quantify quite precisely the relative strength of the antisymmetric field and consequent deviation from general relativity at that epoch.