On the neutral Higgs boson masses in the MSSM for arbitrary stop mixing

We compute the O(alpha (l)alpha (s)) two-loop corrections to the neutral Hi ggs boson masses in the Minimal Supersymmetric extension of the Standard Mo del. An appropriate use of the effective potential allows us to obtain simp le analytical formulae, valid for arbitrary values of m(A) and of the mass parameters in the stop sector. We elucidate some subtleties of the effectiv e potential calculation, and find full agreement with the numerical output of the existing diagrammatic calculation. We discuss in detail the limit of heavy gluino. (C) 2001 Elsevier Science B.V. All rights reserved.