Probing Sterile Neutrino via Lepton Flavor Violating Decays of Mesons

TL;DR

This paper investigates how a GeV-scale sterile neutrino can cause lepton flavor violating decays in mesons, using current experimental limits to constrain the neutrino's mixing parameters across different mass ranges.

Contribution

It calculates box diagram contributions for meson decays induced by sterile neutrinos and derives new constraints on neutrino mixing parameters from experimental data.

Findings

K+→π+ e±μ∓ decay constrains sterile neutrino in the pion-kaon mass range.

B+→π+ e±μ∓ decay dominates constraints in the kaon-B meson mass range.

B0s→μ± e∓ decay at LHCb provides the strongest limit for heavier sterile neutrinos.

Abstract

A sterile neutrino at GeV mass scale is of particular interest in this work. Though not take part in neutrino oscillation, the sterile neutrino can induce flavor violating semileptonic and leptonic decay of $K, D$ and $B$ mesons. We calculated a box diagram contribution in these processes. By making use of current experiment limit of lepton flavor violating decays $M^+_h\to M_l^+\ell_1^+\ell_2^-$ and $M^0\to \ell_1^-\ell_2^+$, we explore the allowed parameter space of $U_{e4}$ and $U_{\mu 4}$ in different mass ranges. Generally speaking, both channels give a limit to the product of $U_{e4}$ and $U_{\mu 4}$. When sterile neutrino mass is located in between pion and kaon mass, $K^+\to \pi^+ e^{\pm}\mu^{\mp}$ gives the strongest constraint while $B^+\to \pi^+ e^{\pm} \mu^{\mp}$ provides the dominated constraint when its mass in between of kaon and B meson. If sterile neutrino is even heavier than B mesons, the $B^0_s\to \mu^{\pm} e^{\mp}$ experiment which is performed at LHCb gives the strongest constraint.