Majorons as cold light dark matter

TL;DR

This paper explores majorons as long-lived dark matter candidates, focusing on their decay signatures into neutrinos and photons, and discusses their potential detectability and role in cosmology.

Contribution

It introduces the concept of majorons as cold dark matter candidates with specific decay channels and discusses their detectability across different mass ranges.

Findings

Majorons can decay into mono-energetic neutrinos detectable by neutrino detectors.

Majoron decay into two photons provides an indirect detection method for keV-scale masses.

Majorons in the keV-MeV range can constitute warm or cold dark matter depending on their production mechanism.

Abstract

Majorons are the Goldstone bosons of spontaneously broken lepton number and hence intimately connected to Majorana neutrino masses. Since all majoron couplings are heavily suppressed by the seesaw scale they are interesting candidates for long-lived dark matter. The signature decay into two mono-energetic neutrinos is potentially detectable with neutrino detectors for majoron masses above MeV and complementary to the loop-induced decays into visible particles. The mass range between keV and MeV can only be probed indirectly with the majoron decay into two photons; keV-scale majorons can be warm or cold dark matter depending on the underlying freeze-in mechanism.