Supersymmetric contributions to rare kaon decays: beyond the single mass-insertion approximation

TL;DR

This paper investigates how supersymmetric models can significantly enhance rare kaon decay rates by extending the mass-insertion approximation to second order, providing a more comprehensive analysis of potential new physics effects.

Contribution

It introduces a second-order mass-insertion approximation in supersymmetric models to accurately evaluate contributions to rare kaon decays, improving upon previous first-order analyses.

Findings

Supersymmetric effects can substantially increase K -> pi nu nu branching ratios.

Second-order mass-insertion terms are crucial for accurate predictions.

Current bounds limit the extent of possible enhancements in decay rates.

Abstract

We analyze the contributions to rare kaon decays mediated by flavor-changing Z-penguin diagrams in a generic low-energy supersymmetric extension of the Standard Model. In order to perform a model-independent analysis we expand the squark mass matrices around the diagonal, following the so called mass-insertion approximation. We argue that in the present case it is necessary to go up to the second order in this expansion to take into account all possible large effects. The current bounds on such second-order term, which was neglected in previous analyses, are discussed in detail and the corresponding upper bounds for the rare kaon decay rates are derived. As a result, we show that supersymmetric effects could lead to large enhancements of K -> pi nu{\bar nu} and K_L -> pi^0 e^+ e^- branching ratios.