# The Case for Low Reheating Temperatures from Gravitational Particle Production and Multi-Stage Reheating

- Institution: CERN
- Speaker: Francesco Costa
- Year: 2026
- Language: English
- Subjects: Physics
- Source: [CERN](https://videos.cern.ch/record/3020981)
- Licence: [CERN](https://copyright.web.cern)
- Who can watch: Tweens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

The early Universe is an efficient source of particle production, particularly for light scalar fields. We study the generation of stable scalars that interact only through gravity, focusing on their production during inflation and throughout single- and multi-stage reheating. Gravitational particle production mechanisms are known to be highly efficient and can easily lead to an overabundant relic density, threatening the viability of non-thermal dark-matter scenarios such as freeze-in. We extend previous studies by deriving the scalar abundance for general reheating histories and demonstrate how additional reheating stages can significantly modify the final relic density. Our results show that avoiding overproduction without fine-tuning the gravitational Wilson coefficients typically requires low reheating temperatures.

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## Lectures

1. [The Case for Low Reheating Temperatures from Gravitational Particle Production and Multi-Stage Reheating](https://invisiblenetwork.ai/learn/cern/3020981/5fefa93f7932), 9 min (CERN's player)