Constraining MeV to 10 GeV Majorons by big bang nucleosynthesis

We estimate the big bang nucleosynthesis (BBN) constraint on the majoron in the mass range between 1 MeV to 10 GeV which dominantly decays into the standard model neutrinos. When the Majoron lifetime is shorter than 1 sec, the injected neutrinos mainly heat up background plasma, which alters the relation between photon temperature and background neutrino temperature. For a lifetime longer than 1 sec, most of the injected neutrinos directly contribute to the protons-to-neutrons conversion. In both cases, deuterium and helium abundances are enhanced, while the constraint from the deuterium is stronger than that from the helium. Li7 abundance gets decreased as a consequence of additional neutrons, but the parameter range that fits the observed Li7 abundance is excluded by the deuterium constraint. We also estimate other cosmological constraints and compare them with the BBN bound. Published by the American Physical Society 2024