On the longitudinal contributions to hadronic tau decay

Abstract

A number of recent determinations of $m_s$ using hadronic $\tau$ decay data involve inclusive analyses based on the so-called $(k,0)$ spectral weights. We show here that the OPE representations of the longitudinal contributions appearing in these analyses, which are already known to be poorly converging, have in addition an unphysical $k$ dependence which produces a significant unphysical decrease in $m_s$ with increasing $k$. We also show how, using additional sum rule constraints, the decay constants of the excited resonances in the strange scalar and pseudoscalar channels may be determined, allowing one to evaluate the longitudinal spectral contributions to the $(k,0)$ sum rules. Taking into account the very-accurately known $\pi$ and $K$ pole contributions, we find that longitudinal contributions can be determined with an accuracy at the few % level, and hence reliably subtracted, leaving an analysis for $m_s$ involving the sum of longitudinal and transverse contributions, for which the OPE representation is much better converged.