Heavy-Neutrino Chirality Enhancement of the Decay $K_L->e\mu$ in Left-Right Symmetric Models

Abstract

We study the decay $K_L->e\mu$ in minimal extensions of the Standard Model based on the gauge groups $SU(2{)}_{L}xU(1{)}_Y$ and $SU(2{)}_{R}xSU(2{)}_{L}xU(1{)}_{B-L}$, in which heavy Majorana neutrinos are present. In $SU(2{)}_{L}xU(1{)}_Y$ models with chiral neutral singlets, $B(K_L->e\mu )$ cannot be much larger than $5x10^{-15}$ without violating other low-energy constraints. In $SU(2{)}_{L}xSU(2{)}_{R}xU(1{)}_{B-L}$ models, we find that heavy-neutrino-chirality enhancements due to the presence of left-handed and right- handed currents can give rise to a branching ratio close to the present experimental limit $B(K_L->e\mu )<3.3x10^{-11}$.

Comments: 16 pages (4 figs appended as a ps file), LaTeX, RAL/94-090 and MZ-TH/94-22