Constraining New Physics in B-->pi+pi- with Reparametrization Invariance and QCD Factorization

Usually, B->pi+pi- decays are expressed in terms of weak amplitudes explicitly dependent on the CKM weak phase alpha or gamma. In this letter, we show that the weak amplitudes can be rewritten such that a manifest dependence on beta emerges instead. Based on this, we constrain new-physics contributions to the CP-violating phase phi_d in B_0 anti-B_0 mixing. Further, we apply reparametrization invariance and use QCD factorization predictions to investigate the bounds on an additional new-physics amplitude in B->pi+pi-.