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We estimate the Big Bang nucleosynthesis (BBN) constraint on the majoron-likeparticle $J$ in the mass range between $1\,{\rm MeV}$ to $10\,{\rm GeV}$ whichdominantly decays into the standard model neutrinos. For a lifetime shorterthan $1\,{\rm sec}$, the majoron heats up the background plasma by injectingneutrinos and changes the relation of photon temperature and backgroundneutrino temperature, resulting in a deficit of $^4 {\rm He}$ abundance and anenhancement of deuterium abundance. When the majoron lifetime is longer than$1\,{\rm sec}$, the injected neutrinos directly convert protons to neutrons,and consequently, the deuterium becomes overabundant. In both cases, theoverabundance of deuterium provides the strongest constraint and it excludesthe parameter range where the $^7 {\rm Li}$ abundance can be explained. We alsoestimate other cosmological constraints and compare them with the BBN bound.

Constraining MeV to 10 GeV majoron by Big Bang Nucleosynthesis