What happened in the early universe? when the universe was optically opaque? in dark sectors?

Credit: Stephan Paul, arXiv:1205.2451

Credit: Stephan Paul, arXiv:1205.2451

Credit: Stephan Paul, arXiv:1205.2451

Electroweak phase transition

• Process by which the Higgs 'switched on'
• In the Standard Model it is a crossover
• Possible in extensions that it would be first order
  ➥ colliding bubbles then make gravitational waves

Credit: [FDL] GRAN via Wikimedia Commons; Morrissey and Ramsey-Musolf, arXiv:1206.2942

What do we do in Helsinki?

• Study (often on lattice) theories of physics beyond the Standard Model with nonperturbative methods:
  • Do they have first-order phase transitions?
  • What regions of parameter space are viable?


• Study (often with simulations) real-time production of gravitational waves from phase transitions:
  • Can we create ansätze for the power spectrum?
  • If we see something at LISA, what can we say about the underlying phyics?

Key parameters

• $T_*$, temperature
  • $T_* \sim 100 \, \mathrm{GeV} \longrightarrow \mathrm{mHz}$ today
• $\alpha_{T_*}$, vacuum energy fraction
• $v_\mathrm{w}$, bubble wall speed
• $H_*/\beta$, 'duration'

These link our two areas of interest:
BSM models and GW production.

Determining the gravitational wave power spectrum

• Given $\{T_*, \alpha_{T_*}, v_\mathrm{w}, \beta/H_*\}$, what GW signal do we get?
• Simulate the transition with an effective model, with:
  • Scalar field $\phi$ (the Higgs 'turning on')
  • Relativistic fluid (everything else - a hot plasma)

Tiny walls to giant bubbles

Fitting everything in is hard

Simulation-based ansätze: PTPlot.org

[Here: $Z_2$-symmetric xSM points from arXiv:1910.13125]

GW reach of SM EFT

At the cutting edge:
strong transitions

(i.e. most of the energy of the universe
is released as latent heat)

Credit: Daniel Cutting

The team

• Mark Hindmarsh, Kari Rummukainen
• Oli Gould, Asier Lopez-Eiguren, Tuomas Tenkanen
• Daniel Cutting, Jani Dahl, Lauri Niemi
• Anna Kormu
• Satumaaria Sukuvaara, Essi Vilhonen