The decay $\tau \to 3\pi {\nu }_{\tau }$ and axial-vector meson $a_1$ in the NJL model

The branching fractions of $\tau \to {\pi }^{+}{\pi }^{-}{\pi }^{-}{\nu }_{\tau }$ and $\tau \to {\pi }^{-}2{\pi }^0{\nu }_{\tau }$ are calculated within the chiral NJL model. Features of the axial-vector $a_1$ meson which plays an important role in describing the $\tau$ decays are discussed. Permissible values for the mass and width of the $a_1$ meson are considered in accordance with the latest experiments.