Gauged $\tau$-lepton chiral currents and $B \to K^{(*)} E_{\rm miss}$

TL;DR

This paper proposes a new light gauge boson linked to tau-lepton chiral currents within a $U(1)_X$ symmetry, explaining recent anomalies in $B$ meson decays and outlining future experimental tests.

Contribution

It introduces a model with a light vector boson coupled to tau-chiral currents that explains recent experimental anomalies and remains consistent with existing constraints.

Findings

A light $m_X \,\simeq 2.1$ GeV boson explains $B o K^{(*)} E_{miss}$ excess.

Model remains consistent with $Z$ decay and direct search constraints.

Distinctive signatures predicted for future high-energy and intensity frontier experiments.

Abstract

We consider a class of theories with a $U(1)_X$ gauge symmetry associated with leptonic chiral currents. The low-energy effective field theory includes a light spin-$1$ boson coupled to the electroweak gauge sector via a Wess-Zumino term, which ensures anomaly cancellation in the infrared. As a concrete application, we show that a light vector boson with mass $m_X \simeq 2.1\,\text{GeV}$, coupled to a $\tau$-lepton chiral current, can readily account for the recent $3\sigma$ excess observed in $B \to K^{(*)} E_{\rm miss}$ at Belle II, while remaining consistent with existing constraints from $Z \to \gamma E_{\rm miss}$ and direct searches for anomalon fields responsible for anomaly cancellation in the ultraviolet. After classifying phenomenologically viable models, we explore in greater detail two concrete realizations which give rise to distinctive phenomenological signatures, potentially accessible at future experiments at the high-energy and intensity frontiers.