The dark side of mSUGRA

We study the mu < 0 branch of the minimal supergravity ansatz of the minimal supersymmetric standard model. The extent to which mu < 0 is disfavoured compared to mu > 0 in global fits is calculated with Markov Chain Monte Carlo methods and bridge sampling. The fits include state-of-the-art two-loop MSSM contributions to the electroweak observables M-W and sin(2) theta(l)(w)(,) as well as the anomalous magnetic moment of the muon (g-2)(mu), the relic density of dark matter and other relevant indirect observables. mu < 0 is only marginally disfavoured in global fits and should be considered in mSUGRA analyses. We estimate that the ratio of probabilities is P(mu < 0)/P(mu > 0) = 0.07-0.16.