Eur. Phys. J. C 23, 121-133 (2002)
https://doi.org/10.1007/s100520100825

Radiative corrections to K_{l 3} decays

¹ Institut für Theoretische Physik, Universität Wien, Boltzmanngasse 5, 1090 Wien, Austria
² Departament de Fìsica Teòrica, IFIC, Universitat de València -- CSIC, Apt. Correus 22085, 46071 València, Spain
³ Centre de Physique Théorique, CNRS Luminy, Case 907, 13288 Marseille -- Cedex 9, France

Received: 12 October 2001
Published online: 11 January 2001

Abstract

We present a complete calculation of the K_{l 3} decays K⁺ → π⁰ l⁺ ν_l and K⁰ → π^- l⁺ ν_l to O(p⁴, (m_d-m_u) p², e² p²) in chiral perturbation theory with virtual photons and leptons. We introduce the concept of generalized form factors and kinematical densities in the presence of electromagnetism, and propose a possible treatment of the real photon emission in K⁺_{l 3} decays. We illustrate our results by applying them to the extraction of the Kobayashi--Maskawa matrix element |V_us| from the experimental K⁺_e3 decay parameters.