Effective-field theory analysis of the τ− → π−π0ντ decays

Abstract

Abstract We perform an effective field theory analysis of the τ − → π − π 0 ν τ decays, that includes the most general interactions between Standard Model fields up to dimension six, assuming left-handed neutrinos. We constrain as much as possible the necessary Standard Model hadronic input using chiral symmetry, dispersion relations, data and asymptotic QCD properties. As a result, we show that it is possible to set precise (competitive with low-energy and LHC measurements) bounds on (non-standard) charged current tensor interactions, finding a very small preference for their presence, according to Belle data. Belle-II near future measurements can thus be very useful in either confirming or further restricting new physics tensor current contributions to these decays. For this, the spectrum in the di-pion invariant mass turns out to be particularly promising. Distributions in the angle defined by the τ − and π − momenta can also be helpful if measured with less than 10% accuracy, both for non-standard scalar and tensor interactions.