Intrinsic flavor violation for massive neutrinos

TL;DR

This paper demonstrates that intrinsic neutrino flavor violation occurs naturally in the Standard Model with massive neutrinos, leading to measurable effects in pion decay processes despite their small magnitude.

Contribution

It provides a detailed calculation of flavor violation probabilities in pion decays within the Standard Model, highlighting effects larger than naive estimates.

Findings

Intrinsic flavor violation occurs in the SM with massive neutrinos.

Calculated nonzero probabilities for flavor-violating pion decays.

Effects are significantly larger than simple theoretical estimates.

Abstract

It is shown that intrinsic neutrino flavor violation invariably occurs when neutrinos are created within the SM augmented by the known massive neutrinos, with mixing and nondegenerate masses. The effects are very small but much greater than the naive estimate $\Delta m^2/E_\nu^2$ or the branching ratio of indirect flavor violating processes such as $\mu\to e\gamma$ within the SM. We specifically calculate the probability (branching ratio) of pion decay processes with flavor violation, such as $\pi\to \mu\bar{\nu}_e$, showing nonzero results.