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[0706.3388]
A Confining Strong FirstOrder Electroweak Phase Transition

Authors:  Germano Nardini, Mariano Quiros, Andrea Wulzer 
Abstract:  In the RandallSundrum model where the radion is stabilized by a
GoldbergerWise (GW) potential there is a supercooled transition from a
deconfined to a confined phase at temperatures orders of magnitude below the
typical Standard Model critical temperature. When the Higgs is localized at the
IR brane the electroweak phase transition is delayed and becomes a strong
firstorder one where the Universe expands by a few efolds. This generates the
possibility of having the outofequilibrium condition required by electroweak
baryogenesis in the electroweak phase transition. We have studied numerically
the region of the GW parameter space where the theory is consistent and the
latter possibility is realized. We have found that in most of the parameter
space the nucleation temperature is so low that sphalerons are totally inactive
inside the bubbles. The condition for sphalerons to be inactive after reheating
imposes an upper bound on the reheating temperature that is weaker for heavy
Higgs bosons so that the outofequilibrium condition seems to favor heavy over
light Higgses. The condition for sphalerons to be active outside the bubbles
puts an upper bound on the number of efolds at the phase transition, roughly
consistent with the critical value required by lowscale inflation to solve the
cosmological horizon problem. 

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Thomas Dent
Joined: 14 Nov 2006 Posts: 28 Affiliation: ITP Heidelberg

Posted: June 25 2007 


This is a suggestion of how to get a nonstandard and strongly first order electroweak phase transition in a particular class of extradimensional theory:
Quote:  In the RandallSundrum model where the radion is stabilized by a GoldbergerWise (GW) potential there is a supercooled transition from a deconfined to a confined phase at temperatures orders of magnitude below the typical Standard Model critical temperature.
When the Higgs is localized at the IR brane the electroweak phase transition is delayed and becomes a strong firstorder one where the Universe expands by a few efolds. 
The RandallSundrum model already has a phase transition which may be seen in 'dual' gauge theory as a deconfinementconfinement transition, or in 5d gravity as the emergence of the IR brane versus the high temperature state of a black hole in AdS space. Then the authors study the behaviour on a more realistic theory with stabilized radion and Higgs. It appears that the electroweak phase transition happens much later and much cooler than in standard 4d cosmology.
One possible spanner in the works is described in
0706.1111
which I noticed a couple of weeks ago. That paper is the latest of many that look at the density in primordial black holes (4d black holes, of course, not 5d!) produced at cosmological phase transitions. One result is that the PBH's forming at strong firstorder transitions overclose the Universe by an enormous factor under quite general assumptions.
However, that is a purely 4d analysis and one might have to think more carefully what could happen in a 5d model.
If RS models all have a strongly firstorder phase transition then the question of PBH formation becomes rather urgent ... has anyone thought about it? 

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