Kaon Decay into Three Photons Revisited

TL;DR

This paper reevaluates the rare decay processes of kaons into three photons within the Standard Model, providing updated estimates for their branching ratios and discussing implications for new physics if measurements exceed these predictions.

Contribution

The paper derives a general decay amplitude form respecting gauge invariance and Bose symmetry, and estimates branching ratios using a chiral-Lagrangian approach, showing they are larger than previous estimates.

Findings

Estimated branching ratio for K_L -> 3 gamma is ~1 x 10^{-14}

Estimated branching ratio for K_S -> 3 gamma is ~2 x 10^{-17}

Predicted rates are significantly higher than earlier calculations

Abstract

We evaluate the rare radiative kaon decays K_{L,S} -> 3 gamma. Applying the requirements of gauge invariance and Bose symmetry, we derive a general form of the decay amplitude, including both parity-conserving and parity-violating contributions. We employ a chiral-Lagrangian approach combined with dimensional analysis arguments to estimate the branching ratios of these decays in the standard model, obtaining values as large as B(K_L -> 3 gamma) ~ 1 x 10^{-14} and B(K_S -> 3 gamma) ~ 2 x 10^{-17}, which exceed those found previously by a few orders of magnitude. Measurements on the branching ratios which are significantly larger than these numbers would likely hint at the presence of new physics beyond the standard model.