Analysis of D_s-> phi pi beyond naive factorization

We analyze the decay $D_s\to \varphi \pi$ with QCD factorization in the heavy quark limit. The nonfactorizable contributions, including hard spectator contribution are discussed and numerical results are presented. Our predictions on the branching ratio of the decay are in agreement with the experiment. We also use a pure phenomenological method to estimate the branching ratio for $D_s\to \varphi \pi$ with the existed $D^0\to K^{\ast }\pi$ data.