The CP-conserving contribution to the transverse muon polarization in K+ -> mu+ nu gamma

摘要

We present a detailed estimate of the transverse muon polarization (P_T) dueto electromagnetic final-state interactions in the decay $K^+ \to \mu^+ \nu\gamma$. This CP-conserving effect represents the dominant contribution to P_Twithin the Standard Model. As a result of an explicit calculation, we find thatthe CP-conserving contribution to P_T is quite small, typically of$\cO(10^{-4})$, essentially due to the suppression factor $\alpha/4\pi^2$. Thisenforces the sensitivity of P_T in probing extensions of the Standard Modelwith new sources of time-reversal violations. A brief discussion about possibleCP-violating contributions to P_T in the framework of supersymmetric modelswith unbroken R-parity is also presented.