# Ricci Reheating

## TL;DR

This paper proposes a gravitational reheating model where a scalar field coupled to Ricci curvature undergoes tachyonic growth during a kination phase, producing high reheating temperatures and a detectable blue-tilted gravitational wave spectrum.

## Contribution

It introduces a novel reheating mechanism involving Ricci scalar coupling and tachyonic growth during kination, linking reheating, leptogenesis, and gravitational wave signatures.

## Key findings

- Reheating temperatures can reach up to 1 GeV.
- The model predicts a blue-tilted gravitational wave spectrum.
- Higgs field could serve as the scalar in low-temperature scenarios.

## Abstract

We present a model for viable gravitational reheating involving a scalar field directly coupled to the Ricci curvature scalar. Crucial to the model is a period of kination after inflation, which causes the Ricci scalar to change sign thus inducing a tachyonic effective mass $m^{2} \propto -H^2$ for the scalar field. The resulting tachyonic growth of the scalar field provides the energy for reheating, allowing for temperatures high enough for thermal leptogenesis. Additionally, the required period of kination necessarily leads to a blue-tilted primordial gravitational wave spectrum with the potential to be detected by future experiments. We find that for reheating temperatures $T_{\rm RH} \lesssim 1$ GeV, the possibility exists for the Higgs field to play the role of the scalar field.