Ultralight dark matter from non-slowroll inflation

TL;DR

This paper proposes a mechanism during non-slowroll inflation that produces ultralight vector dark matter and predicts a unique gravitational-wave background, linking dark matter and primordial black hole physics.

Contribution

It introduces a novel inflationary process involving rapid mass variation of vector fields, leading to ultralight dark matter and associated gravitational waves.

Findings

Generation of ultralight vector dark matter from inflationary dynamics

Prediction of a distinctive low-frequency gravitational-wave background

Connection between dark matter production and primordial black hole scenarios

Abstract

The longitudinal mode of a massive vector field, generated during inflation, offers a well-motivated and phenomenologically rich candidate for dark matter. We show that a rapid variation in the mass of the vector boson, occurring during a brief phase of non-slowroll inflationary evolution, can naturally give rise to extremely small vector masses after inflation ends, corresponding to an ultralight dark matter candidate. This mechanism predicts a stochastic gravitational-wave background, generated at second order by non-adiabatic longitudinal vector fluctuations and amplified at very low frequencies, yielding a distinctive observational signature of the scenario. By leveraging a brief departure from slowroll dynamics during inflation - commonly invoked in scenarios that produce primordial black holes - our framework establishes a novel connection between ultralight vector dark matter and primordial black hole physics, suggesting a possible unified setting for mixed dark matter scenarios.