Antigravity and the big crunch/big bang transition

TL;DR

This paper introduces a Weyl-invariant extension of scalar-tensor theories coupled to gravity, enabling a well-defined, geodesically complete description of cosmological singularities and a natural big crunch/big bang transition involving an antigravity phase.

Contribution

It presents a novel Weyl-invariant framework that allows classical evolution through cosmological singularities, facilitating the construction of complete bouncing cosmologies.

Findings

Classical evolution through singularities is well-defined in the Weyl-invariant extension.

Generic solutions exhibit a big crunch/big bang transition with an antigravity phase.

The approach may aid in developing cyclic or bouncing cosmological models.

Abstract

We point out a new phenomenon which seems to be generic in 4d effective theories of scalar fields coupled to Einstein gravity, when applied to cosmology. A lift of such theories to a Weyl-invariant extension allows one to define classical evolution through cosmological singularities unambiguously, and hence construct geodesically complete background spacetimes. An attractor mechanism ensures that, at the level of the effective theory, generic solutions undergo a big crunch/big bang transition by contracting to zero size, passing through a brief antigravity phase, shrinking to zero size again, and re-emerging into an expanding normal gravity phase. The result may be useful for the construction of complete bouncing cosmologies like the cyclic model.