X-ray photons from late-decaying majoron dark matter

Abstract

An attractive way to generate neutrino masses as required to account for current neutrinooscillation data involves the spontaneous breaking of lepton number. The resultingmajoron may pick up a mass due to gravity. If its mass lies in the kilovolt scale,the majoron can play the role of late-decaying dark matter (LDDM), decayingmainly to neutrinos. In general the majoron has also a sub-dominant decay to twophotons leading to a mono-energetic emission line which can be used as a test of theLDDM scenario. We compare expected photon emission rates with observations inorder to obtain model-independent restrictions on the relevant parameters. Wealso illustrate the resulting sensitivities within an explicit seesaw realization,where the majoron couples to photons due to the presence of a Higgs triplet.