QCD corrections to the masses of the neutralCP-even Higgs bosons in the minimal supersymmetric standard model

We perform a diagrammatic calculation of the leading two-loop QCD corrections to the masses of the neutral $\mathrm{CP}$-even Higgs bosons in the minimal supersymmetric standard model (MSSM). The results are valid for arbitrary values of the parameters of the Higgs boson and scalar top sector of the MSSM. The two-loop corrections are found to reduce the mass of the lightest Higgs boson considerably compared to its one-loop value. The numerical results are analyzed in the grand unified theory favored regions of small and large $\tan \beta .$ Their impact on a precise prediction for the mass of the lightest Higgs boson is briefly discussed.