How to rule out $(g-2)_\mu$ in $U(1)_{L_\mu-L_\tau}$ with White Dwarf Cooling

TL;DR

This paper investigates how white dwarf cooling observations constrain the $U(1)_{L__}$ gauge boson, ruling out parameter regions that could explain the muon $(g-2)$ anomaly and the Hubble tension.

Contribution

It provides the first ab initio calculation of white dwarf neutrino emissivities due to $U(1)_{L__}$ gauge bosons, including the resonant regime, and derives new stellar cooling limits.

Findings

White dwarf observations exclude parameter space explaining $(g-2)__$ and $H_0$ anomalies.

Resonant regime calculations refine the constraints on $A'$ mass and coupling.

White dwarf cooling provides strong bounds on gauged $U(1)_{L__}$ models.

Abstract

In recent years, the gauge group $U(1)_{L_\mu-L_\tau}$ has received a lot of attention since it can, in principle, account for the observed excess in the anomalous muon magnetic moment $(g-2)_\mu$, as well as the Hubble tension. Due to unavoidable, loop-induced kinetic mixing with the SM photon and $Z$, the $U(1)_{L_\mu-L_\tau}$ gauge boson $A'$ can contribute to stellar cooling via decays into neutrinos. In this work, we perform for the first time an \textit{ab initio} computation of the neutrino emissivities of white dwarf stars due to plasmon decay in a model of gauged $U(1)_{L_\mu-L_\tau}$. 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 $(g-2)_\mu$ and $H_0$ 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.