Another look at leptonic photon couplings

AbstractIt may be that additional gauge bosons exist that are associated with unbroken U(1) symmetries; such bosons might couple to some combination of lepton number, and have thus been coined leptonic photons. It can be shown that such gauge forces are restricted to coupling to tau minus muon number Nτ−Nμ. Such gauge bosons can be produced in quantity in the early Universe shortly after the Big Bang. Constraints arising from primordial nucleosynthesis data limit the coupling to α′⩽5×10−18, a significant improvement over previous estimates