Firstorder phase transitions
David J. Weir

University of Helsinki

davidjamesweir
On behalf of the LISA Cosmology Working Group
LISA Symposium, 12 July 2018
Electroweak phase transition
 Process by which the Higgs 'switched on'
 In the Standard Model it is gentle
(crossover)
 Possible (and theoretically
attractive) in extensions that it would experience a
first order phase transition
Source: Morrissey and RamseyMusolf
Motivation
Why study firstorder [electroweak] phase transitions?
 Connects the
biggest mysteries in modern physics:
 Baryogenesis and baryon asymmetry
 Origin of mass  Higgs mechanism
 Dark matter? Inflation? Neutrino masses?
 Difficult to probe the
conditions of the EWPT at colliders
 Use
gravitational waves to see what
happened:
 Then: bubble radius (length scale) close to
$1/H_*$
Now: characteristic frequency mHz
What [still] has a firstorder PT?
 Higgs singlet model  add extra real singlet field
$\sigma$:
difficult to rule out with
colliders [arXiv:1704.05844]
 Two Higgs doublet model  add second complex doublet:
many parameters, quite constrained [arXiv:1405.5537]
 Triplet models  add adjoint scalar field (triplet):
few parameters, not widely studied [arXiv:1802.10500]
 And many, many more...
All have unexcluded regions of parameter space
for which the phase transition is first order.
CosWG report [arXiv:1512.06239]
 Results for a variety of models, at "benchmark points"
 Key result: parametric plots with contours at $\mathrm{SNR}_\text{thr}$
Current PT work in LISA CosWG
 In preparation: update to first report on PTs
 Updated sensitivity curve
 Updated model 'showcase'
 New theoretical work (including no runaways)
 PTPlot web tool for computing SNR
 Modular, containerised
 Code will be open, can be run locally
 Coming soon: early autumn ðŸ˜…
New "PTPlot" tool
Complementarity and multiband
 Breakthrough possibility:
See new physics first, if no deviations seen at LHC
 The three cases (singlet, doublet, triplet) from
earlier all have regions that produce firstorder
phase transitions, that will not be ruled out
by HLLHC.
 Phase transitions produce
substantial backgrounds across wide range of
frequencies
 Use full network of SKA, LISA, ET and
aLIGOaVIRGOKAGRA to constrain parameter space
 Reconstruct parameters: guide collider
experiments
[see Germano Nardini's poster] + arXiv:1806.06463
Recent results 1: parameter space
 "Nonperturbative" results for triplet model [arXiv:1802.10500]
 Dimensional reduction, mapping to existing theory
 Light green region  first order phase transition
 Dark green + gray regions  new simulations required
Recent results 2: spectral shape
 Each simulation: ~1M CPU hours [arXiv:1704.05871]
 Validate spectral shape used
in WG reports
âž¡
[Latetime behaviour? See next talk]
Conclusion
 The electroweak phase transition is 'wide open':
 Colliders cannot (currently) rule out some
scenarios
 Baryogenesis, dark matter, ...
 LISA will be able to detect (or rule out) various
scenarios!
 Understanding of firstorder
phase transitions improving
 Models and parameter spaces
 Microscopic dynamics of the transition
 Gravitational wave power spectrum
You may view this talk later
at: saoghal.net/slides/lisa12/
More info: arXiv:1705.01783