Non-Singular String-Cosmologies From Exact Conformal Field Theories

TL;DR

This paper constructs non-singular string cosmologies in two and three dimensions using exact conformal field theories, revealing quantum effects that can avoid classical singularities and produce diverse cosmological behaviors.

Contribution

It introduces new non-singular cosmological models from exact CFTs, demonstrating quantum corrections can eliminate singularities and enable complex cosmological evolutions.

Findings

All classical singularities are canceled in the exact theories.

Quantum effects can change the sign of scalar curvature over time.

Non-singular cosmologies include oscillating, inflationary, and deflationary models.

Abstract

Non-singular two and three dimensional string cosmologies are constructed using the exact conformal field theories corresponding to SO(2,1)/SO(1,1) and SO(2,2)/SO(2,1). All semi-classical curvature singularities are canceled in the exact theories for both of these cosets, but some new quantum curvature singularities emerge. However, considering different patches of the global manifolds, allows the construction of non-singular spacetimes with cosmological interpretation. In both two and three dimensions, we construct non-singular oscillating cosmologies, non-singular expanding and inflationary cosmologies including a de Sitter (exponential) stage with positive scalar curvature as well as non-singular contracting and deflationary cosmologies. We analyse these cosmologies in detail with respect to the behaviour of the scale factors, the scalar curvature and the string-coupling. The sign of the scalar curvature is changed by the quantum corrections in oscillating cosmologies and evolves with time in the non-oscillating cases. Similarities between the two and three dimensional cases suggest a general picture for higher dimensional coset cosmologies: Anisotropy seems to be a generic unavoidable feature, cosmological singularities are generically avoided and it is possible to construct non-singular cosmologies where some spatial dimensions are experiencing inflation while the others experience deflation.