Exploring non-equilibrium effects in sequential freeze-in

TL;DR

This paper investigates how departures from thermal equilibrium in multi-component dark sectors affect dark matter relic abundance, emphasizing the need for phase-space level analysis over traditional methods.

Contribution

It introduces a phase-space level approach to accurately model non-thermal effects in dark matter freeze-in, revealing significant deviations from standard number-density calculations.

Findings

Deviations up to an order of magnitude in dark matter abundance when considering non-thermal effects.

Non-thermal evolution significantly impacts relic abundance predictions.

Phase-space level computation is crucial for precise dark matter freeze-in modeling.

Abstract

Freeze-in of multi-component dark sectors is governed not only by the interaction with the thermal plasma, but also by their internal dynamics. Full thermalisation within the dark sector is not guaranteed, raising the question of impact of departures from local thermal equilibrium onto the evolution and ultimately relic abundance and momentum distribution of dark matter. In this work we explore this question in a minimal two-scalar model, which can give rise to observable signatures in indirect detection and long-lived particle searches at forward physics experiments. Focusing on the phenomenologically viable regions, we analyse the impact of non-thermal evolution on the dark matter abundance, finding deviations of up to an order of magnitude between the full phase-space treatment and the traditional number-density approach. Our results highlight the importance of phase-space level computation for accurate freeze-in predictions and further motivate dedicated numerical tools for studying the evolution of multi-component dark sectors at the phase space level.