A Resolution of the Cosmological Singularity with Orientifolds

TL;DR

This paper presents a novel string theory-based cosmological model that resolves the initial singularity by introducing orientifolds, leading to a universe with contracting and expanding phases separated by horizons.

Contribution

It introduces a new cosmological scenario involving orientifolds to resolve the initial singularity problem within string theory frameworks.

Findings

The geometry near the singularity matches that of orientifolds.

Boundary conditions and transition amplitudes are well-defined.

A thermal spectrum emerges in the future from the initial vacuum.

Abstract

We propose a new cosmological scenario which resolves the conventional initial singularity problem. The space-time geometry has an unconventional time-like singularity on a lower dimensional hypersurface, with localized energy density. The natural interpretation of this singularity in string theory is that of negative tension branes, for example the orientifolds of type II string theory. Space-time ends at the orientifolds, and it is divided in three regions: a contracting region with a future cosmological horizon; an intermediate region which ends at the orientifols; and an expanding region separated from the intermediate region by a past cosmological horizon. We study the geometry near the singularity of the proposed cosmological scenario in a specific string model. Using D-brane probes we confirm the interpretation of the brane singularity as an orientifold. The boundary conditions on the orientifolds and the past/future transition amplitudes are well defined. Assuming the trivial vacuum in the past, we derive a thermal spectrum in the future.