With the newly available data sets on hadronic tau decays from the B-factories BABAR and BELLE, and future data from BESIII, precise information
on the decay distributions will soon become available. This calls for an
improvement of the decay spectra also on the theoretical side. In this work,
the distribution function for the decay tau --> neutrino_tau K pion will be
presented with the relevant Kaon-pion vector and scalar form factors being
calculated in the framework of the resonance chiral theory, also taking into
account additional constraints from dispersion relations and short-distances.
As a by-product the slope and curvature of the vector form factor
F_+^{K pion}(s) are determined to be lambda_+^{'}=25.6 x 10^{-3} and
lambda_+^{''}=1.31 x 10^{-3} respectively. From our approach it appears
that it should be possible to obtain information on the low lying scalar
K_0^*(800) as well as the second vector K^*(1410) resonances from the
tau decay data. In particular, the exclusive branching fraction of the
scalar component is found to be
B[tau -> neutrino_tau K pion)_{S-wave}]=(3.88 +- 0.19) x 10^{-4}.
Ministerio de Educación y Ciencia, FPA2005-02211, FPA2004-00996,
Generalitat Valenciana, GRUPOS03/013, GV04B-594,GV05/015,
European Commission, EU RTN Network EURIDICE, HPRN-CT2002-00311.
Peer reviewed