Cold light dark matter in extended seesaw models

TL;DR

This paper explores how light dark matter produced via freeze-in in extended seesaw models can have a cold spectrum even at keV masses, impacting structure formation.

Contribution

It demonstrates that quasi-degenerate decays in extended seesaw models can produce cold keV-scale dark matter, with explicit calculations of the transfer function.

Findings

Dark matter can be produced cold at keV masses via quasi-degenerate decays.

The transfer function shows significant impact on structure formation.

Extended seesaw models naturally accommodate this dark matter production mechanism.

Abstract

We present a thorough discussion of light dark matter produced via freeze-in in two-body decays A -> B DM. If A and B are quasi-degenerate, the dark matter particle has a cold spectrum even for keV masses. We show this explicitly by calculating the transfer function that encodes the impact on structure formation. As examples for this setup we study extended seesaw mechanisms with a spontaneously broken global U(1) symmetry, such as the inverse seesaw. The keV-scale pseudo-Goldstone dark matter particle is then naturally produced cold by the decays of the quasi-degenerate right-handed neutrinos.