# Spontaneous dark-matter mass generation along cosmological attractors in string theory

## TL;DR

This paper introduces a novel dark matter production mechanism in heterotic string theory where particles are generated relativistically and then become non-relativistic due to a sudden mass increase triggered by a cosmological phase transition.

## Contribution

It presents a new scenario for dark matter relic density generation involving mass variation driven by string-theoretic phase transitions, differing from standard thermal freeze-out models.

## Key findings

- Dark matter particles are produced relativistically and decouple due to mass increase.
- Mass variation is triggered by condensation of an order-parameter modulus.
- A cosmological attractor mechanism ensures the phase transition occurs.

## Abstract

We propose a new scenario for generating a relic density of non-relativistic dark matter in the context of heterotic string theory. Contrary to standard thermal freeze-out scenarios, dark-matter particles are abundantly produced while still relativistic, and then decouple from the thermal bath due to the sudden increase of their mass above the universe temperature. This mass variation is sourced by the condensation of an order-parameter modulus, which is triggered when the temperature T(t) drops below the supersymmetry breaking scale M(t), which are both time-dependent. A cosmological attractor mechanism forces this phase transition to take place, in an explicit class of heterotic string models with spontaneously broken supersymmetry, and at finite temperature.