Low temperature electroweak phase transition in the Standard Model with hidden scale invariance

Abstract

We discuss a cosmological phase transition within the Standard Model which incorporates spontaneously broken scale invariance as a low-energy theory. In addition to the Standard Model fields, the minimal model involves a light dilaton, which acquires a large vacuum expectation value (VEV) through the mechanism of dimensional transmutation. Under the assumption of the cancellation of the vacuum energy, the dilaton develops a very small mass at 2-loop order. As a result, a flat direction is present in the classical dilaton-Higgs potential at zero temperature while the quantum potential admits two (almost) degenerate local minima with unbroken and broken eletroweak symmetry. We found that the cosmological electroweak phase transition in this model can only be triggered by a QCD chiral symmetry breaking phase transition at low temperatures, T 132 MeV. Furthermore, unlike the standard case, the universe settles into the chiral symmetry breaking vacuum via a first-order phase transition which gives rise to a stochastic gravitational background with a peak frequency ∼ 10 −8 Hz as well as triggers the production of approximately solar mass primordial black holes. The observation of these signatures of cosmological phase transitions together with the detection of a light dilaton would provide a strong hint of the fundamental role of scale invariance in particle physics.

Gravitational waves from a supercooled electroweak phase transition and their detection with pulsar timing arrays

“…It is however of importance for models in which the barrier becomes weaker at low temperature, see e.g. [33,34,56]. Another observation from Table 1 is that the two quantities (R H p ) −1 and α α+1 (which will be important in the next section) approach 1 for lower and lower values of κ.…”

“…2 was mainly introduced as a case of study to illustrate the dynamics of a supercooled and long-lasting PT. We expect other theories to present similar features, especially a class of scale-invariant models with very light scalar particles [33][34][35].…”

“…Therefore, our model differs from previous studies of scale-invariant models [30][31][32] in which the nucleation of true vacuum bubbles occurs at very low temperatures, namely after inflation started. We should note that extreme supercooling [33,34] is also a feature of another class of scale-invariant models of electroweak symmetry breaking with a very light scalar particle [35].…”

LIGO/Virgo Black Holes from a First Order Quark Confinement Phase Transition

“…In Ref. [21], the possibility of a first order QCD transition with electroweak symmetry breaking after QCD confinement has been considered and analyzed in some detail; see also Re.f [22] 3 .…”

“…3 Re.f [22] maintains that M ⊙ PBHs form, as it implicitly assumes that no supercooling takes place according to its adopted underlying theory. Instead, we choose to implement the first order QCD transition through initially suppressed quark Yukawa couplings, assuming electroweak symmetry is broken, thereby avoiding possible difficulties related to vacuum energy domination.…”