[IP2I seminar] P. Schicho (U. Geneva, CH) - Cosmological phase transitions across all length scales

vendredi 11 déc. 2026, 11:00 → 12:00 Europe/Paris

Future gravitational-wave observatories such as LISA could detect a
stochastic background from a first-order phase transition in the early
universe. Such a signal would probe physics at energy scales beyond the
reach of particle colliders and shed light on open questions such as the origin
of the baryon asymmetry, the nature of dark matter, and exotic relics like
primordial black holes.

Predicting this signal requires following the transition across a vast
range of length scales. At the microscopic scales of the hot plasma,
thermal field theory determines the effective potential and the rate at
which bubbles of the new phase nucleate. In between, the interaction of the
bubble walls with the plasma sets how fast the bubbles expand. At
macroscopic scales, colliding bubbles with sound waves and turbulence
source the gravitational waves.

I review recent progress at each of these scales. Thermal effective field
theories that agree with lattice simulations, nucleation rates for strongly
supercooled transitions in which the scale hierarchy shifts across the
bubble, and uncertainty budgets for the bubble wall velocity. I discuss how
automated public tools connect a particle-physics model to its
gravitational-wave spectrum and why the remaining theoretical uncertainties
matter for upcoming experiments.