# A new bound on the low reheating temperature with dark matter

## TL;DR

This paper establishes a lower bound on the reheating temperature of the universe, constrained by dark matter models and ultracompact minihalos observations, impacting early universe cosmology.

## Contribution

It introduces a new lower bound on the reheating temperature based on UCMH constraints, applicable to various dark matter scenarios.

## Key findings

- Reheating temperature lower bound is between 10-100 MeV.
- Constraints derived from gamma-ray observations of UCMHs.
- Potential for future gravitational observations to refine bounds.

## Abstract

We investigate a new bound on the low reheating temperature in a scenario where the Universe experiences early matter-domination before reheating after which the standard big bang cosmology begins. In many models of dark matter (DM), the small scale fluctuations of DM grow during the early matter-domination era and seed the formation of the ultracompact minihalos (UCMHs). Using the constraints on the number of UCMHs from gamma-ray observations, we find a lower bound on the reheating temperature between ${\cal O}(10)~{\rm MeV} - {\cal O}(100)~{\rm MeV}$ for WIMP dark matter depending on the nature of DM. A similar bound could be obtained for non-WIMP dark matter by observing UCMHs gravitationally such as pulsar timing, microlensing and so on in some future observations.