No Open or Flat Bouncing Cosmologies in Einstein Gravity

TL;DR

This paper demonstrates that within Einstein gravity, bouncing open or flat cosmologies are incompatible with string theory constraints, implying the need for theories beyond Einstein gravity to realize such cosmologies.

Contribution

The work shows that bouncing open or flat FRW cosmologies violate string theory constraints in Einstein gravity, highlighting the necessity for extended theories.

Findings

Bouncing open or flat cosmologies are inconsistent with string theory in Einstein gravity.

The Virasoro constraint equates to the null energy condition at leading order.

Beyond Einstein gravity is required for bounce solutions.

Abstract

We show that bouncing open or flat Friedmann-Robertson-Walker cosmologies are inconsistent with worldsheet string theory to first approximation. Specifically, the Virasoro constraint translates to the null energy condition in spacetime at leading order in the alpha-prime expansion. Thus one must go beyond minimally-coupled Einstein gravity in order to find bounce solutions.