Sum rule estimate of the subleading non-perturbative contributions to Bs- anti Bs mixing

We use QCD sum rules to compute the matrix elements of the ΔB=2 operators appearing in the heavy-quark expansion of the width difference of the Bs mass eigenstates. The main focus of our analysis is on the subleading operators R2 and R3, which appear at next-to-leading order in the 1/mb expansion. The matrix elements of these operators are already essential for precise phenomenology, but their calculation in lattice QCD is lacking and the values given here provide a first estimate of their values. We conclude that the violation of the factorization approximation for these matrix elements due to non-perturbative vacuum condensates is as low as 1-2%. (orig.)