Lepton flavor violation with light vector bosons

TL;DR

This paper explores the potential of light vector bosons with lepton-flavor-violating couplings to explain anomalies like the muon's magnetic moment and the proton radius puzzle, highlighting new decay constraints and experimental prospects.

Contribution

It introduces the idea of lepton-flavor-violating light vector bosons and analyzes their decay modes and experimental constraints, expanding the scope of new physics searches.

Findings

Two-body decay mode $ au o mu Z'$ provides strong constraints.

For $M_{Z'} < 2 m_mu$, existing limits surpass previous bounds.

Light vector bosons could explain multiple anomalies in particle physics.

Abstract

New sub-GeV vector bosons with couplings to muons but not electrons have been discussed in order to explain the muon's magnetic moment, the gap of high-energy neutrinos in IceCube or the proton radius puzzle. If such a light Z' not only violates lepton universality but also lepton flavor, as expected for example from the recent hint for $h\to\mu\tau$ at CMS, the two-body decay mode $\tau \to \mu Z'$ opens up and for $M_{Z'} < 2 m_\mu$ gives better constraints than $\tau\to 3\mu$ already with 20-year-old ARGUS limits. We discuss the general prospects and motivation of light vector bosons with lepton-flavor-violating couplings.