Advancing gravitational wave predictions from cosmological first-order phase transitions

25 Aug 2025, 09:00 → 29 Aug 2025, 14:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

Alberto Roper Pol (Universite de Geneve (CH)), Chiara Caprini (CERN), Hyun Min Lee, Jorinde van de Vis (CERN), Philipp Schicho (University of Geneva), Seong Chan Park, Simona Procacci (University of Geneva (CH))

As the detection of a stochastic gravitational wave background from the early universe becomes increasingly promising, signals from hypothetical first-order phase transitions are attracting growing interest. Predicting these signals often requires the solution of plasma dynamics at macroscopic scales, which, in turn, depends on the phenomena that characterize the phase transition at microscopic scales. 
Therefore, various assumptions on distinctive scales and their separation are usually employed to enable concrete evaluations. 
This workshop aims to bring together researchers from both the microscopic and macroscopic communities to collaboratively address theoretical shortcomings and refine current gravitational wave spectral templates across different regimes.

1. Microscopic scales – Quantitative uncertainties affect the fundamental phase transition parameters within minimal scenarios beyond the Standard Model, where a scalar field drives the symmetry-breaking mechanism.

2. Intermediate scales – Different approaches have been employed to describe the interactions between the scalar field and the plasma, including bubble wall dynamics and plasma viscosity. A key question is, e.g., whether the bubble wall runs away or reaches a terminal velocity.

3. Macroscopic scales – Several approximations are used to connect to large-scale phenomena during and after the phase transition, such as collisions between the bubbles, the development of turbulence, and the evolution of sound shells.

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Confirmed speakers:

1.	2.	3.
Bogumila Swiezewska, U. Warsaw	Wen-Yuan Ai, U. Vienna	Jani Dahl, U. Helsinki
Anna Kormu, U. Helsinki	Ryusuke Jinno, U. Kobe	Lorenzo Giombi, U. Helsinki
Joonas Hirvonen, U. Nottingham	Benoit Laurent, U. McGill	Mark Hindmarsh, U. Helsinki
Mikko Laine, U. Bern	Andrew J. Long, Rice U.	Tina Kahniashvili, U. Carnegie Mellon
Kari Rummukainen, U. Helsinki	Andrii Dashko, DESY	Thomas Konstandin, DESY
	Carlo Branchina, U. Calabria	Antonino S. Midiri, U. Geneva
	Marek Lewicki, U. Warsaw	Tae Hyun Jung, IBS
	Csaba Balazs, Monash U.

 

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Format: online participation is possible, but in-person attendance is limited. Talks are in person.

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Registration: the deadline is on May 30, 2025. The call for abstracts is open until June 14, 2025.

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This event is sponsored by the Department of Theoretical Physics at CERN as well as the CERN-Korea collaboration program.

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Organizing committee:

Chiara Caprini (CERN & University of Geneva)

Hyun Min Lee (Chung-Ang University)

Seong Chan Park (Yonsei University)

Simona Procacci (University of Geneva)

Alberto Roper Pol (University of Geneva)

Philipp Schicho (University of Geneva)

Jorinde van de Vis (CERN)

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NOTE: several participants have received phishing messages offering to book accommodation for the event. We do not send such messages as all participants need to make their own accommodation arrangements.

Monday 25 August

10:00 → 10:30 Welcome & coffee

10:30 → 12:00 Microscopic scales: Morning session

10:30 TBA

Speaker: Bogumila Swiezewska (University of Warsaw)

11:15 TBA

Speaker: Anna Kormu

12:00 → 13:30 Lunch break

13:30 → 15:00 Microscopic scales: Afternoon session

13:30 Thermal nucleation in perturbation theory

Cosmological first-order phase transitions may have generated an observable gravitational wave background, providing a unique window into physics beyond the Standard Model. A crucial step in predicting this background is the reliable computation of bubble nucleation rates. In this talk, I will discuss how techniques, such as effective field theories, Boltzmann equations and real-time simulations, enhance our understanding of perturbative nucleation rate computations in high-temperature quantum field theories, leading to more robust predictions. I will also highlight remaining challenges in perturbative methods, outlining directions for future progress in this field.

Speaker: Joonas Hirvonen (University of Nottingham)

14:15 An effective-theory perspective on bubble nucleation and growth

Certain aspects of phase transition dynamics, at least the initial nucleations and subsequent growth, can be described within the framework of fluctuating hydrodynamics, extended by a scalar order parameter. A strength of this formulation is that the contributions of small and large momenta can be factorized. We describe the ideas and limitations behind this approach, and how it can be used for determining the small-gradient limit of the friction term that appears in the equation of motion of the Higgs field.

Speaker: Mikko Sakari Laine (Universitaet Bern (CH))

15:00 → 15:30 Coffee break

15:30 → 17:00 Microscopic scales: Afternoon session

Tuesday 26 August

09:15 → 10:00 Microscopic scales: Morning session

09:15 TBA

Speaker: Dr Taehyun Jung (Institute for Basic Science)

10:00 → 10:30 Coffee break

10:30 → 12:00 Intermediate scales: Morning session

10:30 TBA

Speaker: Benoit Laurent (CEA / DAM Ile de France (FR))

11:15 TBA

Speaker: Wen-Yuan Ai

12:00 → 13:30 Lunch break

13:30 → 15:00 Intermediate scales: Afternoon session

13:30 TBA

Speaker: Mr Andrii Dashko (DESY Theory)

14:15 TBA

Speaker: Andrew Long (Rice University)

15:00 → 15:30 Coffee break

15:30 → 17:00 Intermediate scales: Afternoon session

Wednesday 27 August

09:15 → 10:00 Intermediate scales: Morning session

09:15 Bubble wall dynamics and the electroweak phase transition

The dynamics of of the electroweak phase transition has profound implications for cosmology and particle physics, and is governed by the density perturbations generated by the expanding bubble. A precise determination of this dynamics, and in particular of the bubble wall velocity, is crucial to assess the experimental signatures of the transition. In this talk, I will report on recent advances in the quantitative theoretical description of bubble dynamics, and, adopting typical benchmark models, present numerical results for the wall velocity and the profiles that describe the phase transition dynamics. A near-universal behaviour across models will emerge and be discussed.

Speaker: Carlo Branchina (Università della Calabria)

10:00 → 10:30 Coffee break

10:30 → 12:00 Intermediate scales: Morning session

10:30 TBA

Speaker: Dr Marek Lewicki (University of Warsaw)

11:15 From symmetries to gravitational waves: a self-consistent calculation

Predicting the gravitational wave spectrum from symmetry breaking in the early universe during first-order phase transitions is key to understanding these symmetries. In this talk I present our recent advancements in developing a self-consistent framework for predicting such gravitational wave spectra. Our approach enhances existing calculations by providing a more comprehensive treatment of the underlying physics, from the particle physics model to the hydrodynamic evolution of bubbles and the resulting gravitational wave production. The talk will emphasize how this self-consistency refines gravitational wave predictions and explore its implications for understanding early universe cosmology.

Speaker: Csaba Balazs (Monash University)

12:00 → 13:30 Lunch break

13:30 → 15:00 Special contribution: Colloquim

13:30 Theory colloquium

Speaker: Kari Rummukainen

18:30 → 22:00 Social dinner

Thursday 28 August

09:15 → 10:00 Macroscopic scales: Morning session

09:15 TBA

Speaker: Thomas Konstandin

10:00 → 10:30 Coffee break

10:30 → 12:00 Macroscopic scales: Morning session

10:30 TBA

Speaker: Tinatin Kakhniashvili

11:15 TBA

Speaker: Antonino Salvino Midiri (Universite de Geneve (CH))

12:00 → 13:30 Lunch break

13:30 → 15:00 Macroscopic scales: Afternoon session

13:30 TBA

Speaker: Lorenzo Giombi (University of Helsinki)

14:15 Decay of acoustic turbulence and the resulting gravitational wave predictions

For a wide range of scenarios, the generation of gravitational waves (GWs) from cosmological first-order phase transitions is believed to be dominated by sound waves. Understanding their decay through acoustic turbulence is an important factor in determining the overall intensity of the GW signal. We have simulated acoustic turbulence numerically in three dimensions to study its decay properties and apply them to estimate the resulting GW power spectrum. We find that including the decay leads to shallower power laws in the spectrum, with the predicted steep $k^9$ power law of the non-decaying case only appearing in the slow decay limit.

Speaker: Jani Dahl

15:00 → 15:30 Coffee break

15:30 → 17:00 Macroscopic scales: Afternoon session

Friday 29 August

09:15 → 10:00 Macroscopic scales: Morning session

09:15 TBA

Speaker: Ryusuke Jinno (Kobe University)

10:00 → 10:30 Coffee break

10:30 → 12:00 Special contribution: Final overview

10:30 TBA

Speaker: Prof. Mark Hindmarsh (University of Helsinki, University of Sussex)