Precision analysis of the masses of the neutral Higgs bosons in the MSSM

The masses of the neutral CP-even Higgs bosons in the Minimal Supersymmetri c Standard Model (MSSM) are predicted on the basis of explicit Feynman-diag rammatic calculations. The results, containing the complete diagrammatic on e-loop corrections, the leading two-loop corrections of O(alpha alpha(s)) a nd further improvements taking into account leading electroweak two-loop an d higher-order QCD contributions, are discussed and compared with results o btained by renormalization group calculations. Good agreement is found in t he case of vanishing mixing in the scalar top sector, while sizable deviati ons occur if scalar top mixing is taken into account. By means of a Taylor expansion a compact approximation formula for the mass of the lightest Higg s boson, m(h), is derived. The quality of the approximation in comparison w ith the full result is analyzed.