Speaker
Description
In this talk, I will introduce the Big Bang nucleosynthesis (BBN) constraint on the majoron-like particle in the mass range between 1MeV to 10GeV which dominantly decays into the standard model neutrinos. For a lifetime shorter than 1 sec, the majoron heats up the background plasma by injecting neutrinos and changes the relation of photon temperature and background neutrino temperature, resulting in a deficit of 4He abundance and an enhancement of deuterium abundance. When the majoron lifetime is longer than 1 sec, the injected neutrinos directly convert protons to neutrons, and consequently, the deuterium becomes overabundant. In both cases, the overabundance of deuterium provides the strongest constraint and it excludes the parameter range where the 7Li abundance can be explained. We also estimate other cosmological constraints and compare them with the BBN bound.
