Classically and Quantum stable Emergent Universe from Conservation Laws

TL;DR

This paper introduces a class of emergent universe models from scale invariant two measures theories that are both classically stable and resistant to semiclassical collapse, due to a symmetry preventing the scale factor from shrinking below a minimum value.

Contribution

It demonstrates that certain emergent universes derived from scale invariant two measures theories can achieve classical stability and avoid semiclassical collapse, unlike previous models.

Findings

Emergent universes from two measures theories can be classically stable.

A symmetry in the emergent phase prevents collapse.

The scale factor cannot be smaller than a minimum value.

Abstract

It has been recently pointed out by Mithani-Vilenkin that certain emergent universe scenarios which are classically stable are nevertheless unstable semiclassically to collapse. Here, we show that there is a class of emergent universes derived from scale invariant two measures theories with spontaneous symmetry breaking (s.s.b) of the scale invariance, which can have both classical stability and do not suffer the instability pointed out by Mithani-Vilenkin towards collapse. We find that this stability is due to the presence of a symmetry in the "emergent phase", which together with the non linearities of the theory, does not allow that the FLRW scale factor to be smaller that a certain minimum value $a_0$ in a certain protected region.