Meson dominance in the “second class” $\tau \to \eta \pi {\nu }_{\tau }$ decay

Motivated by recent estimates of the isospin-violating process $\tau \to \eta \pi {\nu }_{\tau }$, mostly relying on the $\rho$ and $a_0$ dominance of the relevant form factors near threshold, we present an assessment for the branching ratio that accounts for additional, potential effects from the lowest radial excitations ${\rho }^{\prime }\equiv \rho (1450)$ and $a_0^{\prime }\equiv a_0(1450)$, respectively, also lying in the decay phase space.