The Dark Side of mSUGRA

We study the μ < 0 branch of the minimal supergravity ansatz of the minimal supersymmetric standard model. The extent to which μ < 0 is disfavoured compared to μ > 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 MW and sin 2 θ w, as well as the anomalous magnetic moment of the muon (g − 2)μ, the relic density of dark matter and other relevant indirect observables. μ < 0 is only marginally disfavoured in global fits and should be considered in mSUGRA analyses. We estimate that the ratio of probabilities is P (μ < 0)/P (μ > 0) = 0.07− 0.16.