# Bounce in GR and higher-order derivative operators

## TL;DR

This paper demonstrates that stable, nonsingular cosmologies can be achieved within General Relativity by incorporating higher-order derivative operators of scalar fields, challenging the notion that modifications to GR are necessary for such solutions.

## Contribution

It shows that higher-order derivative operators in scalar-tensor theories enable stable nonsingular cosmologies within GR without requiring modifications.

## Key findings

- Stable nonsingular cosmologies are possible within GR using higher-order derivatives.
- Higher-order operators do not introduce instabilities at energies below the Planck scale.
- This approach challenges the need for modifying GR to violate the null energy condition.

## Abstract

Recent progress seems to suggest that one must modify General Relativity (GR) to stably violate the null energy condition and avoid the cosmological singularity. However, with the higher-order derivative operators of scalar field (a subclass of the degenerate higher-order scalar-tensor theory), we show that at energies well below the Planck scale, fully stable nonsingular cosmologies can actually be implemented within GR.