Global Effective-Field-Theory analysis of New-Physics effects in (semi)leptonic kaon decays

TL;DR

This paper uses an effective field theory framework to analyze kaon and pion decays, providing bounds on new physics effects, and compares these constraints with collider search results.

Contribution

It offers a comprehensive global analysis of semileptonic kaon decays within an EFT approach, including simultaneous Wilson coefficient fits and reinterpretation in terms of high-energy operators.

Findings

Derived bounds on Wilson coefficients from decay data.

Reinterpreted the $V_{ud}-V_{us}$ diagram as a new physics constraint.

Compared low-energy bounds with LHC collider search limits.

Abstract

We analyze the decays $K\to\pi\ell\nu$ and $P\to\ell\nu$ ($P=K,\pi$, $\ell=e,\,\mu$) using a low-energy Effective-Field-Theory approach to parametrize New Physics and study the complementarity with baryon $\beta$ decays. We then provide a road map for a global analysis of the experimental data, with all the Wilson coefficients simultaneously, and perform a fit leading to numerical bounds for them and for $V_{us}$. A prominent result of our analysis is a reinterpretation of the well-known $V_{ud}-V_{us}$ diagram as a strong constraint on new physics. Finally, we reinterpret our bounds in terms of the $SU(2)_L\times~U(1)_Y$-invariant operators, provide bounds to the corresponding Wilson coefficients at the TeV scale and compare our results with collider searches at the LHC.