  We carry out lattice simulations of a cosmological electroweak phase
transition for a Higgs mass m_h ~ 126 GeV. The analysis is based on a
dimensionally reduced effective theory for an MSSM-like scenario including a
relatively light coloured SU(2)-singlet scalar, referred to as a right-handed
stop. The non-perturbative transition is stronger than in 2-loop perturbation
theory, and may offer a window for electroweak baryogenesis. The main remaining
uncertainties concern the physical value of the right-handed stop mass which
according to our analysis could be as high as m_tR ~ 155 GeV; a more precise
effective theory derivation and vacuum renormalization than available at
present are needed for confirming this value.
