NSPT estimate of the improvement coefficient $c_A$ to two loops

By using Numerical Stochastic Perturbation Theory (NSPT), we carry out a quenched two-loop computation of the improvement coefficient $c_A$ associated to the isovector axial current. Within the Schr"odinger Functional formalism, we compute the bare quark mass $m$ and fix $c_A$ by requiring discretization corrections on $m$ to be of order $O(a^2)$ in the lattice spacing $a$.