First-order restoration of SU(N-f) x SU(N-f) chiral symmetry with large N-f and an electroweak phase transition

It has been argued by Pisarski and Wilczek that finite temperature restoration of SU(N-f) x SU(N-f) chiral symmetry is first order for N-f >= 3. This type of chiral symmetry with large N-f may appear in the Higgs sector if one considers models such as walking technicolor theories. We examine the first-order restoration of chiral symmetry from the point of view of the electroweak phase transition. The strength of the transition is estimated in a SU(2) x U(1) gauged linear sigma model by means of the finite temperature effective potential at one loop with the ring improvement. Even if the mass of the neutral scalar boson corresponding to the Higgs boson is larger than 114 GeV, the first-order transition can be strong enough for electroweak baryogenesis, as long as the extra massive scalar bosons (required for the linear realization) are kept heavier than the neutral scalar boson. Explicit symmetry breaking terms reduce the strength of the first-order transition, but the transition can remain strongly first order even when the masses of pseudo Nambu-Goldstone bosons become as large as the current lower bound of direct search experiments.