We consider the 2-loop finite temperature effective potential for a Standard
Model-like Higgs boson, allowing Higgs boson couplings to additional scalars.
If the scalars transform under color, they contribute 2-loop diagrams to the
effective potential that include gluons. These 2-loop effects are perhaps
stronger than previously appreciated. For a Higgs boson mass of 115 GeV, they
can increase the strength of the phase transition by as much as a factor of
3.5. It is the analogue of this effect that is responsible for the survival of
the tenuous electroweak baryogenesis window of the Minimal Supersymmetric
Standard Model. We further illuminate the importance of these 2-loop diagrams
by contrasting models with colored scalars to models with singlet scalars. We
conclude that baryogenesis favors models with light colored scalars. This
motivates searches for pair-produced di-jet resonances or jet(s) + missing
energy.Comment: 12 pages, 5 figures; v2: minor changes, journal versio
