Dark lepton superfluid in protoneutron stars

We find that sub-GeV neutrino portal bosons that carry lepton number can condense inside a protoneutron star (newly born neutron star). These bosons are produced copiously and form a Bose-Einstein condensate for a range of as yet unconstrained coupling strengths to neutrinos. The condensate is a lepton number superfluid with transport properties that differ dramatically from those encountered in ordinary dense baryonic matter. We discuss how this phase could alter the evolution of protoneutron stars and comment on the implications for neutrino signals and nucleosynthesis.