Eur. Phys. J. C (2008) 53: 401-412
https://doi.org/10.1140/epjc/s10052-007-0464-7

Regular Article - Theoretical Physics

Analyticity constraints on the strangeness changing vector current and applications to τ→Kπν_τ and τ→Kππν_τ

Groupe de Physique Théorique, Institut de Physique Nucléaire, CNRS/IN2P3, Université Paris-Sud 11, 91406, Orsay, France

^* e-mail: moussall@ipno.in2p3.fr

Received: 11 October 2007
Revised: 22 October 2007
Published online: 29 November 2007

Abstract

We discuss matrix elements of the strangeness changing vector current using their relation, due to analyticity, with πK scattering in the P-wave. We take into account experimental phase-shift measurements in the elastic channel as well as results, obtained by the LASS collaboration, on the details of inelastic scattering, which show the dominance of two quasi-two-body channels at medium energies. The associated form factors are shown to be completely determined, up to one flavor symmetry breaking parameter, imposing boundary conditions at t=0 from chiral and flavor symmetries and at t→∞ from QCD. We apply the results to the τ→Kπν_τ and τ→Kππν_τ amplitudes and compare the former to recent high statistics results from B factories.