First-order restoration of SU(Nf) x SU(Nf) chiral symmetry with large Nf and Electroweak phase transition

TL;DR

This paper investigates the first-order restoration of SU(Nf) x SU(Nf) chiral symmetry at finite temperature, exploring its implications for electroweak phase transition strength and baryogenesis in models with large Nf.

Contribution

It provides an analysis of the electroweak phase transition in models with large Nf, demonstrating conditions under which the transition remains strongly first-order.

Findings

First-order transition can be strong enough for baryogenesis even with a Higgs mass >114 GeV.

Heavy scalar bosons can coexist with a strong first-order transition.

Explicit symmetry breaking reduces but does not eliminate the transition's strength.

Abstract

It has been argued by Pisarski and Wilczek that finite temperature restoration of the chiral symmetry SU(Nf) x SU(Nf) is first-order for Nf >=3. This type of chiral symmetry with a large Nf may appear in the Higgs sector if one considers models such as walking technicolor theories. We examine the first-order restoration of the chiral symmetry from the point of view of the electroweak phase transition. The strength of the transition is estimated in 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 the 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.