Theoretical estimate of the $D^* \to D\pi$ decay rate

We present the results of our lattice QCD study of the $g_{D^* D\pi}i$ coupling, relevant to the $D^\ast \to D\pi$ decay. Our computation is made on the gauge field configurations that include $N_f=2$ dynamical light quarks by using the twisted mass QCD action. From the results obtained at four different lattice spacings we were able to take for the first time the continuum limit of this quantity computed on the lattice. Our final value, $g_c=0.53(3)(3)$, leads to $\Gamma(D^{\ast +}\to \bar{D}^0 \pi^+)= (50\pm 5\pm 6)$ keV, and is in good agreement with the experimental results for the width of the charged $D^\ast$-meson.