Violation of CP and T in semileptonic decays due to scalar interactions

TL;DR

This paper investigates how scalar interactions involving $W^{}$ and $H^{}$ bosons can lead to CP and T violation in semileptonic decays of $K^{}$ mesons and $ au^{}$ leptons, providing bounds based on experimental data.

Contribution

It introduces a model analyzing scalar-mediated interference effects as a source of CP and T violation in semileptonic decays, linking experimental bounds to theoretical predictions.

Findings

Current bounds on $K^+_{}$ decays limit CP violation in $ au$ decays.

Predicted CP-violating effects in $ au$ decays are smaller than previous estimates.

Scalar interactions can induce measurable CP and T violation in semileptonic processes.

Abstract

Observing charge-parity (CP) or time-reversal (T) violations in the leptonic sector will give useful information to elucidate the nature of neutrinos. CP-violating couplings in charged leptonic currents carry out the weak phases necessary to break these symmetries. Here we study the interference of $W^{\pm}$ and $H^{\pm}$ bosons mediated amplitudes as the origin of possible CP and T violation in semileptonic decays of $K^{\pm}$ mesons and $\tau^{\pm}$ leptons. We use the experimental bound on the T-odd transverse polarization asymmetry in $K^+_{\mu 3}$ decays to predict an upper limit on the CP violating effects in $\tau \to K \pi \nu$ decays. In the framework of this model with scalar-mediated interactions, we find that current limits on the former process indicate that the CP violating effects in the latter are much smaller than the limits reported so far.