Impact of Supercooling on Direct Searches for Dark Matter and Gravitational Wave Backgrounds

TL;DR

This paper explores how supercooling during cosmological phase transitions influences dark matter production and gravitational wave signals, revealing new parameter spaces for detection and linking two observational avenues.

Contribution

It introduces the first detailed analysis of supercooling effects on dark matter freeze-out and freeze-in, highlighting their impact on detection prospects and gravitational wave signatures.

Findings

Supercooling can shift WIMP-like dark matter candidates into allowed regions.

Freeze-in candidates become more accessible to current experiments.

Low-frequency gravitational wave spectra are affected by finite-duration reheating.

Abstract

An interesting feature of a cosmological phase transition can be a stage of exponential expansion (supercooling). The modified expansion history and the entropy injection at reheating, can affect the final energy fraction of dark matter. In this paper, we revisit the calculation of the freeze-out and freeze-in dynamics, showing additional effects on top of the standard dilution factor if the dark matter production is completed during the supercooling stage. We show for the first time how these effects can be particularly interesting for direct detection, as the parameter space for WIMP-like candidates shifts from excluded to allowed regions, and freeze-in candidates get closer to experimental reach. A phenomenological motivation to consider supercooling is the associated gravitational wave background. The implications of a finite-duration reheating stage, when the equation of state is close to matter-domination, are a peculiar low-frequency spectrum, and its shift to lower frequencies. These effects are a complementary test of the dynamics that we study for dark matter production, and remarkably can link direct detection of dark matter and gravitational wave astronomy.