Mixing effects in the finite-temperature effective potential of the MSSM with a light stop

We incorporate the effects of mixing arising from the trilinear terms in the MSSM potential to the effective three-dimensional theory for the MSSM at high temperature in the limit of large mA. There are relevant one-loop effects that modify the 3D parameters of the effective theory. We calculate the two-loop effective potential of the 3D theory for the Higgs and the right handed stop to analyse the possible phase transitions and to determine the precise region in the m_h-m_t2 plane for which the sphaleron constraint for preservation of the baryon asymmetry is satisfied. There is an upper bound on the value of the mixing parameter coming from stop searches. We also compare with previous results obtained using 4D calculations of the effective potential for the regime of large m_Q. A two-stage phase transition persists for a small range of values of m_t2 for given values of the mixing parameter and tanβ. This can further constrain the allowed region of parameter space. Electroweak baryogenesis requires a value of m_t2 ≲ 170 and m_h ≲ 105 GeV for m_Q = 300 GeV.