Upper bounds on SUSY contributions to b to s transitions from B_s - B_sbar mixing

We study the constraints on supersymmetric contributions to b to s transitions from the recent allowed range for B_s-B_sbar mixing obtained by the D0 collaboration at the Tevatron. We compute the upper bounds on the relevant off-diagonal squark mass terms and compare them with the bounds coming from Delta F=1 decays. We find that the constraints on chirality-flipping mass insertions are unaffected. Conversely, the upper bound on $B_s-\bar B_s$ mixing is effective in constraining chirality-conserving mass insertions, and it has striking effects in the case in which left- and right-handed insertions have similar size. Finally, we discuss the phase of the B_s-B_sbar mixing amplitude in the presence of SUSY contributions.