Lepton-flavor violating decays induced by Lorentz violation in the Yukawa sector of the Standard Model Extension

Abstract

Tree-level lepton-flavor-violating decays induced by Lorentz-violating effects within the Yukawa sector of the Standard Model Extension are studied. These new physics effects are parameterized by the $(Y_{f})_{\mu\nu}^{AB}$ tensor, with $\mu$ and $\nu$ denoting Lorentz indices and $A$, $B$ being indices in the flavor space. Since this tensor is antisymmetric under the interchange of Lorentz indices, in analogy with the electromagnetic tensor $F_{\mu\nu}$, $(Y_{f})_{\mu\nu}^{AB}$ can be expressed in terms of six components associated with two complex three-vectors denoted by $\mathbf{e}_l^{AB}$ and $\mathbf{b}_l^{AB}$. On the assumption that these three-vectors are pure real or pure imaginary and mutually orthogonal, constraints on their magnitudes via experimental bounds on lepton-flavor-violating processes $\mathrm{Br}(l_B\rightarrow \gamma l_A)$ and $\mathrm{Br}(l_B\rightarrow l_A l_C \bar{l}_C)$ are estimated. Thus, the $l_B\rightarrow \gamma l_A$ decay provides the following upper bounds: $\lvert \mathbf{e}_l^{\mu\tau} \lvert < 1.51\times 10^{-11}$ , $\lvert \mathbf{e}_l^{e\tau} \lvert < 1.34 \times 10^{-11}$, $\lvert \mathbf{e}_l^{e\mu} \lvert < 3.65 \times 10^{-18}$, $\lvert \mathbf{b}_l^{\mu\tau} \lvert < 1.95\times 10^{-11}$, $\lvert \mathbf{b}_l^{e\tau} \lvert <1.73\times 10^{-11}$, $\lvert \mathbf{b}_l^{e\mu} \lvert < 4.71\times 10^{-18}$. Conversely, by assuming that the Lorentz-violating parameters are purely real, for the $l_B\rightarrow l_A l_C \bar{l}_C$ process it is found that $\lvert \mathbf{e}_l^{\mu\tau}\lvert< 3.05 \times 10^{-12}$ and $\lvert \mathbf{b}_l^{\mu\tau}\lvert< 4.31 \times 10^{-12}$. These results offer more restrictive bounds than those previously reported in the literature.