Theoretical update of B s − B s mixing

We update the theory predictions for the mass difference ∆M s , the width difference ∆Γ s and the CP asymmetry in flavour-specific decays, a s fs , for the B s −B s system. In particular we present a new expression for the element Γ s 12 of the decay matrix, which enters the predictions of ∆Γ s and a s fs. To this end we introduce a new operator basis, which reduces the troublesome sizes of the 1/m b and α s corrections and diminishes the hadronic uncertainty in ∆Γ s /∆M s considerably.