The strongly coupled fourth family and a first-order electroweak phase transition (I) quark sector

TL;DR

This paper investigates whether models with a strongly coupled fourth family of quarks can produce a strong first-order electroweak phase transition suitable for baryogenesis, analyzing effective theories with and without compositeness conditions.

Contribution

It provides a detailed analysis of the electroweak phase transition in models with a fourth family, highlighting the conditions under which the transition is strongly first order or weakly first order.

Findings

Without the compositeness condition, a strong first-order transition is possible within certain parameter ranges.

Imposing the compositeness condition weakens the phase transition, making it possibly second order.

For fourth-family quark masses of 330-480 GeV, the transition is not strongly first order, challenging baryogenesis scenarios.

Abstract

In models of dynamical electroweak symmetry breaking due to strongly coupled fourth-family quarks and leptons, their low-energy effective descriptions may involve multiple composite Higgs fields, leading to a possibility that the electroweak phase transition at finite temperature is first order due to the Coleman-Weinberg mechanism. We examine the behavior of the electroweak phase transition based on the effective renormalizable Yukawa theory which consists of the fourth-family quarks and two SU(2)-doublet Higgs fields corresponding to the bilinear operators of the fourth-family quarks with/without imposing the compositeness condition. The strength of the first-order phase transition is estimated by using the finite-temperature effective potential at one-loop with the ring-improvement. In the Yukawa theory without the compositeness condition, it is found that there is a parameter region where the first-order phase transition is strong enough for the electroweak baryogenesis with the experimentally acceptable Higgs boson and fourth-family quark masses. On the other hand, when the compositeness condition is imposed, the phase transition turns out to be weakly first order, or possibly second order, although the result is rather sensitive to the details of the compositeness condition. Combining with the result of the Yukawa theory without the compositeness condition, it is argued that with the fourth-family quark masses in the range of 330-480 GeV, corresponding to the compositeness scale in the range of 1.0-2.3 TeV, the four-fermion interaction among the fourth-family quarks does not lead to the strongly first-order electroweak phase transition.