Comment on new physics contributions to Gamma_{12}^s

A recent measurement by the D0 collaboration finds a like-sign di-muon charge asymmetry in the B system that is roughly 3 sigma larger than the value predicated by the Standard Model. This suggests new physics contributing to B-Bbar mixing. For the current central value of the CP asymmetry, the required size of Gamma_{12}^s is larger than Standard Model estimates of this quantity. In this paper, we will explore the constraints on new physics contributions to Gamma_{12}^s. We show that there are two dimension six operators of Standard Model fields in the electroweak Hamiltonian whose coefficients are not constrained enough to rule out possible contributions from new physics. We argue that a more precise measurement of tau(B_s)/tau(B_d), which is possible with currently available data, could either support or strongly constrain the existence of new physics in Gamma_{12}^s.

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