New constraint from supernova explosions on light particles beyond the Standard Model

We propose a new constraint on light (sub-GeV) particles beyond the Standard Model that can be produced inside the proto-neutron star core resulting from the core-collapse supernova explosion. It is derived by demanding that the energy carried by exotic particles being transferred to the progenitor stellar envelopes must not exceed the explosion energy of $\lesssim 2\cdot 10^{51}$~erg of observed supernovae. We show specifically that for the case of dark photon which kinetically mixes with the SM photon and decays predominantly to an $e^\pm$ pair, smaller mixing parameter of one order of magnitude below the well-established supernova cooling bound can be excluded. Furthermore, our bound fills the gap between the cooling bound and the region constrained by (non-)observation of $\gamma$-rays produced from supernovae for dark photon lighter than $\sim 20$~MeV.