Effective field theory approach to lepton number violating decays $K^\pm\rightarrow \pi^\mp l^{\pm}l^{\pm}$: short-distance contribution

TL;DR

This paper develops an effective field theory framework to analyze lepton number violating kaon decays, connecting high-energy new physics operators to low-energy observables and deriving constraints from experimental data.

Contribution

It provides a systematic analysis of all dimension-9 operators causing LNV in kaon decays, including their QCD renormalization and matching to chiral perturbation theory and SMEFT.

Findings

Derived decay rate formulas parameterized by Wilson coefficients and LECs.

Set new bounds on SMEFT Wilson coefficients from experimental limits.

Established a comprehensive EFT approach for hadronic LNV decays.

Abstract

This is the first paper of our systematic efforts on lepton number violating (LNV) hadronic decays in the effective field theory approach. These decays provide information complementary to popular nuclear neutrinoless double-$\beta$ ($0\nu\beta\beta$) decay in that they can probe LNV interactions involving heavier quarks and charged leptons. We may call them hadronic $0\nu\beta\beta$ decays in short, though $\beta$ refers to all charged leptons. In this work we investigate the decays $K^\pm\rightarrow\pi^\mp l^{\pm}l^{\pm}$ that arise from short-distance or contact interactions involving four quark fields and two charged lepton fields, which have canonical dimension nine (dim-9) at leading order in low energy effective field theory (LEFT). We make a complete analysis on the basis of all dim-9 operators that violate lepton number by two units, and compute their one-loop QCD renormalization effects. We match these effective interactions in LEFT to those in chiral perturbation theory ($\chi$PT) for pseudoscalar mesons, and determine the resulting hadronic low energy constants (LECs) by chiral symmetry and lattice results in the literature. The obtained decay rate is general in that all physics at and above the electroweak scale is completely parameterized by the relevant Wilson coefficients in LEFT and hadronic LECs in $\chi$PT. Assuming the standard model effective field theory (SMEFT) is the appropriate effective field theory between some new physics scale and the electroweak scale, we match our LEFT results to SMEFT whose leading effective interactions arise from LNV dim-7 operators. This connection to SMEFT simplifies significantly the interaction structures entering in the kaon decays, and we employ the current experimental bounds to set constraints on the relevant Wilson coefficients in SMEFT.