  In extensions of the Standard Model with no dimensionful parameters the
electroweak phase transition can be delayed to temperatures of order 100 MeV.
Then the chiral phase transition of QCD can proceed with 6 massless quarks. The
top-quark condensate destabilizes the Higgs potential through the Yukawa
interaction, triggering the electroweak transition. Based on the symmetries of
massless QCD, it has been argued that the chiral phase transition is first
order. We point out that the top-Higgs Yukawa interaction is nonperturbatively
large at the QCD scale, and that its effect on the chiral phase transition may
not be negligible, violating some of the symmetries of massless QCD. The
remaining symmetries indicate that top quarks condense in a second-order phase
transition, but top condensation might also be triggered by a first-order
symmetry-breaking transition in the light-quark sector.
