Estimate of the branching fraction ${\tau }^{-}\to \eta {\pi }^{-}{\nu }_{\tau }$, the $a_0^{-}(980)$, and non-standard weak interactions

Shmuel Nussinov, Abner Soffer

We consider the ``second-class current'' decay ${\tau }^{-}\to {\pi }^{-}\eta {\nu }_{\tau }$ from several points of view. We first focus on the decay rate as expected within standard weak interaction and QCD du…