The decay $\tau\rightarrow f_1 \pi \nu_\tau$ in the Nambu--Jona-Lasinio   model
  The width of the decay $\tau\rightarrow f_1 \pi \nu_\tau$ has recently been measured by the BaBar experiment. The estimation of this width is given in the framework of the NJL model with the axial-vector mesons. Prediction is in agreement with the experimental data. It is shown that the $\pi-a_1$ transition contribution plays an important role and allows us to bring the NJL prediction to the data. 
A. V. Vishneva, M. K.Volkov and D. G. Kostunin
hep-ph