# Repulsive gravity induced by a conformally coupled scalar field implies a bouncing radiation-dominated universe

## TL;DR

This paper explores how a conformally coupled scalar field can induce repulsive gravity effects, leading to a bouncing radiation-dominated universe, which challenges traditional cosmological models.

## Contribution

It demonstrates that a scalar field with broken symmetry can produce gravitational repulsion and a bounce in a radiation-dominated universe, a novel insight into early universe dynamics.

## Key findings

- Repulsive gravity arises from a conformally coupled scalar field in broken symmetry state.
- A bouncing universe is the unique solution under these conditions.
- The model suggests alternative early universe scenarios with gravitational repulsion.

## Abstract

In the present work we revisit a model consisting of a scalar field with a quartic self-interaction potential non-minimally (conformally) coupled to gravity [1]. When the scalar field vacuum is in a broken symmetry state, an effective gravitational constant emerges which, in certain regimes, can lead to gravitational repulsive effects when only ordinary radiation is coupled to gravity. In this case, a bouncing universe is shown to be the only cosmological solution admissible by the field equations when the scalar field is in such a broken symmetry state.