Abstract
The effect of perturbative infrared singularities on the finite-temperature effective potential in the standard model with a light Higgs boson is investigated. Together with the Coleman-Weinberg term, it promotes the full gauge-symmetry breaking. The transition to the U(1) vacuum via quantum tunneling is expected to occur at some temperature ∼100 MeV. However, without knowledge of dynamical details, one cannot conclusively decide whether the chiral or the (full) gauge symmetry breaks first.