Detecting first-order electroweak phase transitions with LISA

David Weir [he/him/his] - davidjamesweir

HIP and University of Helsinki

Helsinki LISA day, 27.2.2020

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:

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

GW reach of SM EFT

Source: arXiv:1903.11604

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

Research goals

  • Next few years: GW Cosmology for LISA
    • Cutting-edge simulations of the early universe
    • Microscale (Monte Carlo) to macroscale (hydro)
    • Dark and visible sectors

  • After that: The Energy and Gravity Frontiers
    • Electroweak phase transition and beyond:
      CEPC (2030-), ILC (2035-)
    • Finnish role in European GW missions:
      Einstein Telescope (2030-), LISA (2034-)
    • Complementarity between GW and colliders