Gravitational waves from early universe phase transitions

arXiv:1704.05871

David J. Weir - University of Helsinki - davidjamesweir

PRACEdays18, 29 May 2018

What happened when the universe was optically opaque?

Original source: arXiv:1205.2451

Questions:

What are the observable gravitational wave signatures of cosmological processes?
What can we say about physics beyond the Standard Model with gravitational waves?

Goal:

Simulation pipeline from particle theory to GW observation

What's next: LISA

Three laser arms, 2.5 M km separation
ESA’s L3 mission, launch by 2034
Proposal submitted last year 1702.00786
Officially adopted on 20.6.2017

First order thermal phase transitions

Higgs 'turns on': bubbles nucleate and grow
Bubbles expand in plasma - reaction fronts form
Bubbles + fronts collide
Sound waves in plasma ➝ GWs
Endgame: turbulence?

Key science for LISA

Science Investigation 7.2: Measure, or set upper limits on, the spectral shape of the cosmological stochastic GW background.

Operational Requirement 7.2: Probe a broken power-law stochastic background from the early Universe as predicted, for example, by first order phase transitions ...

Coupled field and fluid system

Ignatius, Kajantie, Kurki-Suonio and Laine

Scalar $\phi$ (the Higgs) and ideal fluid $u^\mu$ (plasma):
- Split stress-energy tensor $T^{\mu\nu}$ into field and fluid bits $$\partial_\mu T^{\mu\nu} = \partial_\mu (T^{\mu\nu}_\phi + T^{\mu\nu}_\text{fluid}) = 0$$
- Parameter $\eta$ sets the scale of friction due to plasma $$\partial_\mu T^{\mu\nu}_\phi = \tilde \eta \frac{\phi^2}{T} u^\mu \partial_\mu \phi \partial^\nu \phi $$
- Create reaction front in the plasma that propagates outward with the bubble