WIMP-like Dark Matter Without Thermalization At Freeze-Out

TL;DR

This paper explores a hidden-sector dark matter model where decoupling at high temperatures still results in the correct relic abundance, with very weak couplings to the Standard Model, challenging detection prospects.

Contribution

It introduces a scenario where dark matter decouples early and evolves separately, yet achieves the observed relic density with minimal Standard Model interaction.

Findings

Comparable annihilation cross sections are achievable in high-temperature decoupled hidden sectors.

The model predicts extremely small couplings, making detection difficult.

Relic abundance is maintained despite the sectors' separate thermal histories.

Abstract

In the standard thermal relic scenario, dark matter remains in chemical equilibrium with the Standard Model radiation bath until freeze-out occurs at $T \sim m_X/20$, where $m_X$ is the dark matter mass. In this familiar class of models, the observed relic density is obtained for annihilation cross sections of order $\sigma v \sim 10^{-26}$ cm$^3$/s. We show that comparable cross sections can naturally be realized in hidden-sector models in which the dark matter and Standard Model sectors decouple at a very high temperature, $T \gg m_X$, and subsequently evolve with separate thermal histories. Despite this decoupling, the two sectors have similar temperatures during freeze-out, leading to the usual thermal relic abundance. As a consequence, the coupling between the Standard Model and hidden sectors can be extremely small, potentially placing direct detection and collider signals far below foreseeable sensitivities.