Eur. Phys. J. C (2005) 40: 205-227
https://doi.org/10.1140/epjc/s2005-02123-3

theoretical physics

Radiative K _e3 decays revisited

¹ Institut für theoretische Physik, Universität Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
² Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Nussallee 14-16, 53115, Bonn, Germany
³ Dipartimento di Fisica Teorica, Universitá degli Studi di Trieste, 34100, Trieste, Italy
⁴ INFN-Trieste, Strada Costiera 11, 34100, Trieste, Italy
⁵ Departamento de Física Teórica y del Cosmos, Universidad de Granada, Campus de Fuente Nueva, 18002, Granada, Spain

Abstract

Motivated by recent experimental results and ongoing measurements, we review the chiral perturbation theory prediction for decays. Special emphasis is given to the stability of the inner bremsstrahlung-dominated relative branching ratio versus the K _e3 form factors, and on the separation of the structure-dependent amplitude in differential distributions over the phase space. For the structure-dependent terms, an assessment of the order p ⁶ corrections is given, in particular, a full next-to-leading order calculation of the axial component is performed. The experimental analysis of the photon energy spectrum is discussed, and other potentially useful distributions are introduced.