Exploring non-equilibrium effects in sequential freeze-in

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Hauptverfasser: Chatterjee, Shiuli, Hryczuk, Andrzej
Format: Preprint
Veröffentlicht: 2026
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author Chatterjee, Shiuli
Hryczuk, Andrzej
author_facet Chatterjee, Shiuli
Hryczuk, Andrzej
contents 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.
format Preprint
id arxiv_https___arxiv_org_abs_2604_14688
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Exploring non-equilibrium effects in sequential freeze-in
Chatterjee, Shiuli
Hryczuk, Andrzej
High Energy Physics - Phenomenology
Cosmology and Nongalactic Astrophysics
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.
title Exploring non-equilibrium effects in sequential freeze-in
topic High Energy Physics - Phenomenology
Cosmology and Nongalactic Astrophysics
url https://arxiv.org/abs/2604.14688