Cosmological Perturbations in Antigravity

TL;DR

This paper analyzes how cosmological perturbations evolve in a Weyl-symmetric two-scalar-field theory that features cyclic solutions with brief antigravity phases, revealing stability despite unconventional kinetic terms.

Contribution

It introduces a novel Weyl-symmetric model with cyclic cosmology and demonstrates perturbative stability despite the presence of a wrong-signed kinetic term.

Findings

Cyclic solutions include brief antigravity phases.

Perturbations remain stable despite wrong-signed kinetic term.

Model connects to conformal Standard Model extensions.

Abstract

We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely-signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the Standard Model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically-complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity", during each successive transition from a Big Crunch to a Big Bang. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, its cosmological solutions are stable at the perturbative level.