SUPERSYMMETRIC ELECTROWEAK PHASE-TRANSITION - DIMENSIONAL REDUCTION VERSUS EFFECTIVE POTENTIAL

We compare two methods of analyzing the finite-temperature electroweak phase transition in the minimal supersymmetric standard model: the tr aditional effective potential (EP) approach, and the mote recently adv ocated procedure of dimensional reduction (DR). The latter tries to av oid the infrared instabilities of the former by matching the full theo ry to an effective theory that has been studied on the lattice. We poi nt out a limitation of DR that caused a large apparent disagreement wi th the effective potential results in our previous work. We also incor porate wave function renormalization into the EP, which is shown to de crease the strength of the phase transition. In the regions of paramet er space where both methods are expected to be valid, they give simila r results, except that the EP is significantly more restrictive than D R for the range of baryogenesis-allowed values of tan beta, m(h), the critical temperature, and the up-squark mass parameter m(u). In contra st, the DR results are consistent with 2 less than or similar to tan b eta less than or similar to 4, m(h) less than or similar to 80 GeV, an d m(u) sufficiently large to have universality of the squark soft-brea king masses at the GUT scale, in a small region of parameter space. We suggest that the differences between DR and EP are due to higher-orde r perturbative corrections rather than infrared effects. (C) 1998 Else vier Science B.V.