Two-loop corrections to radiative electroweak symmetry breaking in the MSSM

We study the O(alpha(t)alpha(s) + alpha(t)(2)) two-loop corrections to the minimization conditions of the MSSM effective potential, providing compact analytical formulae for the Higgs tadpoles. We connect these results with the renormalization group running of the MSSM parameters from the grand unification scale down to the weak scale, and discuss the corrections to the Higgs mixing parameter mu and to the running CP-odd Higgs mass MA in various scenarios of gravity-mediated SUSY breaking. We find that the O(alpha(t)alpha(s)) and O(alpha(t)(2)) contributions partially cancel each other in the minimization conditions. In comparison with the full one-loop corrections, the O(alpha(t)alpha(s)+alpha(t)(2)) two-loop corrections significantly weaken the dependence of the parameters mu and MA on the renormalization scale at which the effective potential is minimized. The residual two-loop and higher-order corrections to it and m(A) are estimated to be at most 1% in the considered scenarios. (C) 2003 Elsevier Science B.V. All rights reserved.