Lepton Flavor Violating Decays of $B$ and $K$ Mesons in Models with Extended Gauge Group

TL;DR

This paper explores lepton flavor violating decays of $K$ and $B$ mesons within extended gauge models involving lepto-quarks, deriving bounds on new physics couplings from experimental limits and proposing tests for future experiments.

Contribution

It constructs effective Lagrangians for LFV meson decays in extended gauge models and derives bounds on new physics couplings from experimental data.

Findings

Upper bound on effective coupling $(G_X/G_F)^2 < 1.1 imes 10^{-10}$ from $K^0_L$ decay

Bound $(G_X/G_F)^2 < 10^{-10}$ from $K^-$ decay to $ uar{ u}$

Discussion of decay modes for testing extended gauge models in experiments

Abstract

Lepton Flavor Violating (LFV) decays are forbidden in the Standard Model (SM) and to explore them one has to go beyond it. The flavor changing neutral current induced Lepton Flavor Conserving and LFV decays of $K$ and $B$ mesons are discussed in the gauge group $G = SU(2)_L\times U(1)_{Y_1}\times SU(2)_X$. The lepto-quark $X^{\pm 2/3}_{\mu}$ corresponding to gauge group $ SU(2)_X$ allows the quark-lepton transitions and hence giving a framework to construct the effective Lagrangian for the LFV decays. The mass of lepto-quark $m_{X}$ provides a scale at which the gauge group $G$ is broken to the SM gauge group. Using the most stringent experimental limit $\mathcal{B}(K^{0}_{L}\to \mu^{\mp}e^{\pm}) < 1.7 \times 10^{-12}$, the upper bound on the effective coupling constant $(\frac{G_{X}}{G_F})^2 < 1.1 \times 10^{-10}$ is obtained for certain pairing of lepton and quark generations in the representation $(2, \bar{2})$ of the group $G$. Later, the effective Lagrangian for the LFV meson decays for the gauge group $G = \left[SU(2)_{L}\times SU(2)_{R}\times U(1)_{Y_1^{\prime}}\right]\times SU(2)_{X}$ is constructed. Using $\mathcal{B}(K^{-} \to \pi^{-}\nu \bar{\nu}) = (1.7 \pm 1.1)\times 10^{-10}$, the bound on the ratio of effective couplings is obtained to be $\left(\frac{G_{X}}{G_{F}}\right)^2 < 10^{-10}$. A number of decay modes are discussed which provide a promising area to test this model in the current and future particle physics experiments.