QCD-induced electroweak phase transition

Abstract

Phase transitions associated with nearly conformal dynamics are known to lead to significant supercooling. A notorious example is the phase transition in RandallSundrum models or their CFT duals. In fact, it was found that the phase transition in this case is first-order and the tunneling probability for the radion/dilaton is so small that the system typically remains trapped in the false vacuum and the phase transition never completes. The universe then keeps expanding and cooling. Eventually the temperature drops below the QCD scale. We show that the QCD condensates which subsequently form give an additional contribution to the radion/dilaton potential, an effect which had been ignored so far. This significantly reduces the barrier in the potential and allows the phase transition to complete in a substantially larger region of parameter space. Due to the supercooling, electroweak symmetry is then broken simultaneously. This class of models therefore naturally leads to an electroweak phase transition taking place at or below QCD temperatures, with interesting cosmological implications and signatures.

Detecting gravitational waves from cosmological phase transitions with LISA: an update

“…One may wonder whether the TeV-brane terms breaking conformality are necessary to guarantee the occurrence of the PT. As recently noticed in [36], such terms are not required. In all Randall-Sundrum models where the SM gauge fields, in particular the SU (3) gauge bosons, live in the bulk, the running of the QCD coupling is a function of the 5D radius.…”

“…It follows that the parameter region leading to a strong radion PT is far larger than that obtained by overlooking the effects of the radion on the QCD scale. In particular, the previously overlooked region of parameter space naturally exhibits a radion PT that is extremely supercooled (T n ∼ Λ QCD T c ) and extraordinary strong [36]. In this framework, the EWPT is naturally induced by QCD confinement and provides a compelling target for LISA.…”

“…In CH models, since the Higgs arises only when a non-zero condensate χ forms, the confinement PT and the EWPT are naturally linked. Nevertheless, until recently, past studies considered them separately, focusing either on the confinement PT, described by the dynamics of a dilaton/radion and relying on a 5D description [28][29][30][31][32][33][34][35][36]39] as discussed in the previous subsection, or assumed that the EWPT takes place after the confinement of the strongly-coupled sector [69,159,172,173]. The confinement PT is generically very strong, and is known to produce very large GW signals [29,32,39].…”

Peccei-Quinn phase transition at LIGO

“…To address this phase transition quantitatively, we will follow the strongly coupled models studied in Ref. [35][36][37] which have a weakly-coupled five-dimensional version via holography. This helps to reduce the number of parameters, although the conclusions can be extended to models without holographic versions [36].…”

“…Finally, let us conclude this subsection by noting that in principle an alternative option for a long period of supercooling is to have λ(T ) evolving too slow (for a holographic example see [41])) such that the condition Γ H 4 is not met and the universe gets trapped in the unconfined phase. As discussed in [35,36], the universe could still exit supercooling at the QCD scale, where a new contribution to the dilaton potential arises. In order for this to happen, we need the strong sector to have constituents which are charged under SU (3) c .…”