The mass of the lightest MSSM Higgs boson: A compact analytical expressionat the two-loop level

A compact approximation formula for the mass of the lightest neutral CP-eve n Higgs boson, m(h), in the Minimal Supersymmetric Standard Model (MSSM) is derived from the diagrammatic two-loop result for m(h) up to O(alpha alpha (s)). By analytically expanding the diagrammatic result, the leading logari thmic and non-logarithmic as well as the dominant subleading contributions are obtained. The approximation formula is valid for general mixing in the scalar top sector and arbitrary choices of the parameters in the Higgs sect or of the model. Its quality is analysed by comparing it with the full diag rammatic result. The agreement we find with the full result is better than 2GeV for most parts of the MSSM parameter space. (C) 1999 Elsevier Science B.V. All rights reserved.