Light MSSM Higgs boson mass to three-loop accuracy

The light CP even Higgs boson mass, M-h, is calculated to three-loop accuracy within the Minimal Supersymmetric Standard Model (MSSM). The result is expressed in terms of (DR) over bar DR parameters and implemented in the computer program H3m. The calculation is based on the proper approximations and their combination in various regions of the parameter space. The three-loop effects to M-h are typically of the order of a few hundred MeV and opposite in sign to the two-loop corrections. The remaining theory uncertainty due to higher order perturbative corrections is estimated to be less than 1GeV.