Dispersive representation and shape of K_{l3} form factors

TL;DR

This paper develops a model-independent dispersive parametrization of K_{l3} form factors to test electroweak couplings and analyze decay measurements, enabling precise predictions and extraction of fundamental parameters.

Contribution

It introduces a novel dispersive approach for K_{l3} form factors and applies it to improve predictions and parameter extractions in kaon decays.

Findings

Predicted the ratio Gamma(K_{mu3})/Gamma(K_{e3}) with high accuracy.

Extracted |f_+(0)V_{us}| from experimental data.

Discussed potential measurement of isospin breaking asymmetry.

Abstract

The Callan-Treiman low-energy theorem offers an opportunity to test electroweak couplings of light quarks to the gauge boson W. To that aim, we introduce a model-independent and accurate dispersive parametrization of the two K_{l3} form factors. We then discuss three applications to the analysis of K_{e3} and K_{mu3} measurements: the prediction of the ratios Gamma(K_{mu3})/Gamma(K_{e3}), the extraction of |f_+(0)V_{us}| and finally the possible measurement of m_u - m_d induced isospin breaking asymmetry.