How to rule out (g − 2)μ in $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ with white dwarf cooling

Abstract

In recent years, the gauge group $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ U 1 L μ − L τ has received a lot of attention since it can, in principle, account for the observed excess in the anomalous muon magnetic moment (g − 2)μ, as well as the Hubble tension. Due to unavoidable, loop-induced kinetic mixing with the SM photon and Z, the $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ U 1 L μ − L τ gauge boson A′ can contribute to stellar cooling via decays into neutrinos. In this work, we perform for the first time an ab initio computation of the neutrino emissivities of white dwarf stars due to plasmon decay in a model of gauged $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$ U 1 L μ − L τ . A key result is that current observations of the early-stage white dwarf neutrino luminosity at the 30% level exclude previously allowed regions of the parameter space favoured by a simultaneous explanation of the (g – 2)μ and H0 anomalies. In this work, we present the relevant white dwarf cooling limits over the entire A′ mass range. In particular, we have performed a rigorous computation of the luminosities in the resonant regime, where the A′ mass is comparable to the white dwarf plasma frequencies.