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	Andrii Dashko, DESY	Tina Kahniashvili, U. Carnegie Mellon
Kari Rummukainen, U. Helsinki	Carlo Branchina, U. Calabria	Thomas Konstandin, DESY
Pablo Navarrete, U. Helsinki	Marek Lewicki, U. Warsaw	Antonino S. Midiri, U. Geneva
	Csaba Balazs, Monash U.	Tae Hyun Jung, IBS

 

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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

1 Welcome & coffee

2 Introduction

Speaker: Simona Procacci (University of Geneva (CH))

intro.pdf

Recording

Video preview

Microscopic scales: Morning session

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microscopic scales:
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2830 8284

Convener: Philipp Schicho (University of Geneva)

discussion_microscopic_scales_results.pdf

3 Precise predictions for cosmological phase transitions

In this talk, I will discuss how to formulate precise predictions for the parameters of supercooled cosmological first-order phase transitions. I will explain the construction of the high-temperature effective field theory (EFT) applicable to the issue of nucleation. Using this EFT, I will show how to consistently formulate predictions at next-to-leading order in perturbation theory, paying special attention to the issue of various mass/energy scales and how they vary across the bubble.

Speaker: Bogumila Swiezewska (University of Warsaw)

B_Swiezewska.pdf

Recording

Video preview

4 An update on non-perturbative calculations for strong phase transitions

Nucleation rate computations are of broad importance in particle physics and cosmology. Previously, these nucleation rates have generally been calculated perturbatively, but those calculations depend on the semiclassical picture of the bubble and its fluctuations, and different orders of perturbative calculation yield very different results. In this talk, I will give you an update on results of our lattice calculations of the nucleation rate. We focused on a real scalar theory with a tree-level potential barrier and performed nonperturbative simulations to determine the nucleation rate, computing a final result extrapolated to the thermodynamic and continuum limits. Although the system in question should be well-described by a complete one-loop perturbative calculation, we find only qualitative agreement with the full perturbative result. Our result motivates further testing of the current nucleation paradigm.

Speaker: Anna Kormu

An update on nonperturb pts.pdf

Recording

Video preview

12:00 Lunch break

Microscopic scales: Afternoon session

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microscopic scales:
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2830 8284

Convener: Hyun Min Lee

discussion_microscopic_scales_results.pdf

5 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)

Recording

slides.pdf

Video preview

6 Cosmological phase transitions without high-temperature expansions

Accurate determination of equilibrium thermal parameters in strong first-order phase transitions — in particular, the critical
temperature and latent heat — is essential for predicting gravitational-wave signals detectable by upcoming spaceborne observatories.

In perturbation theory, the evaluation of the thermal effective potential for such strong transitions is hampered by the presence of
large masses in the Higgs phase. This prompts the question of how to properly resum the soft sector while accounting for heavy masses,
and calls for new ways to tackle the computation of fully massive thermal sum-integrals at the multiloop level.

In this talk, we put forward a perturbative framework for computing the full four-dimensional effective potential across all mass regimes.
The key advance is a unified treatment of both hard and soft scales within a single expression, enabling consistent numerical evaluation of
fully massive sum-integrals to three loops and beyond via the so-called hot Loop–Tree Duality. This approach may yield accurate
predictions in beyond-the-Standard-Model scenarios featuring strong transitions that are relevant for gravitational-wave observatories.

Speaker: Pablo Navarrete (University of Helsinki)

PN_workshopCERN_v11.pdf

Recording

Video preview

15:00 Coffee break

Microscopic scales: Short talks

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microscopic scales:
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2830 8284

Convener: Philipp Schicho (University of Geneva)

discussion_microscopic_scales_results.pdf

7 Higher-order-operator corrections to phase transitions parameters in dimensional reduction

The construction of 3D EFTs for phase transition (PT) computations has been taken to unprecedented levels of precision in the recent years, considering effects up to 3-loop order. However, the contributions from higher-dimensional effective operators (EO) that arise at the same order in the power counting have been generally neglected in the literature.

In this talk, we will analyze the effect of these EO in a model resembling the Higgs sector of the SMEFT up to dimension 6, in the strong transition regime. Finally, we will highlight the challenges to overcome to extend these computations to more complex models.

Speaker: Luis Gil (Universidad de Granada)

Gil_HigherDim_2025.pdf

Recording

Video preview

8 Finite-temperature bubble-nucleation with shifting scale hierarchies

Focusing on supercooled PTs in models with classical scale symmetry, we investigate the limitations of derivative expansions in constructing a thermal EFT description for bubble nucleation. We show that derivative expansion for gauge field fluctuations diverges because the gauge field mass varies strongly between the high- and low-temperature phases. By computing the gauge fluctuation determinant, we show that these effects can be captured while accounting for large explicit logarithms at two loops. We show how this construction can improve nucleation rate calculations, providing a more robust framework for describing GW from supercooled PT in models like 4the SU(2)cSM.

Speaker: Maciek Kierkla

cern_advgwpt25_mkierkla.pdf

Recording

Video preview

9 RG-improved Partial Dressing Thermal REsummation for accurate Veff calculations within and beyond the high-T approximation

We consistently RG-improve the 4D perturbative imaginary time formalism calculation of the scalar effective potential at finite temperature using the partial dressing thermal resummation scheme. This avoids overcounting, is easy to implement numerically using only one-loop results, gives results with high precision comparable to dimensional reduction calculations in the high-T regime, but is also under control and of useful precision beyond the high-T regime for strong phase transitions.

Speaker: David Richard Curtin (University of Toronto)

2025.08.25 David Curtin RGI OPD FTQFT CERN workshop phase transitions talk_5m.pdf

Recording

Video preview

Microscopic scales: Panel discussion

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microscopic scales:
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2830 8284

Convener: Philipp Schicho (University of Geneva)

discussion_microscopic_scales_results.pdf

18:00 Reception

The reception will be served in the "Glassbox" of the canteen.

Tuesday 26 August

Microscopic scales: Morning session

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microscopic scales:
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2830 8284

Convener: Alberto Roper Pol

discussion_microscopic_scales_results.pdf

10 Bubble nucleation vs phase mixing around the spinodal temperature

Phase transitions, in general, involve a nonzero spinodal temperature at which the potential barrier disappears. In some models of cosmological first-order phase transitions, supercooling is maintained until around the spinodal temperature, so the phase transition proceeds during the time when the potential barrier disappears rapidly. In this talk, I will discuss whether, in this circumstance, the phase transition is completed via bubbles or phase mixing driven by the growth of tachyonic modes. Based on our numerical simulations solving the Langevin equation, we conclude that the bubble nucleation picture is still valid even if the width and height of the potential barrier are smaller than the temperature scale. Therefore, the standard analysis based on bubble nucleation rate is applicable, assuming the bubble nucleation rate is properly calculated.

Speaker: Taehyun Jung (Institute for Basic Science)

FOPT_spinodal_CERN.pptx

FOPT_spinodal_CERN_without_video.pdf

Recording

10:00 Coffee break

Intermediate scales: Morning session

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intermediate scales:
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6832 1667

Convener: Alberto Roper Pol

discussion_intermediate_scales_results.pdf

11 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))

cern25.pdf

Recording

12 Microscopic particle processes during bubble expansion and new high-frequency gravitational waves

In certain scenarios, bubble walls may reach a velocity with a very large Lorentz boost factor or run away. For such ultrarelativistic bubble walls, a new energy scale $\gamma_w T$ emerges, allowing for the production of heavy particles. I will discuss the dynamics of ultrarelativistic bubble walls and the associated heavy dark matter and gravitational wave production.

Speaker: Wen-Yuan Ai

CERN_WenyuanAi_Aug_2025.pdf

Recording

12:00 Lunch break

Intermediate scales: Afternoon session

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intermediate scales:
https://www.menti.com/al7v358nsur8
6832 1667

Convener: Seong Chan Park

discussion_intermediate_scales_results.pdf

13 Bubble-wall velocity with loop corrections

In this work, the dynamics of the nucleating scalar field is investigated during
the first-order phase transitions by incorporating one-loop corrections of classical fluctuations.
We contrast our results with traditional methods based on the derivative expansion; show that the latent heat can differ from the effective-potential result; and discuss general hydrodynamic corrections.
Finally, an application of the presented framework for a simple scalar field model is shown, finding that the one-loop improvement decreases the wall speed and that an effective-potential approximation underestimates full one-loop corrections.

Speaker: Andrii Dashko (DESY Theory)

Advancing-GW-CERN-2025.pdf

Recording

14 Bounds on bubble wall velocity and application to first-order QCD phase transition

In this talk, I will take advantage of recent progress on wall speed determination to provide simple estimates that constrain the wall velocity between two opposite limits: local thermal equilibrium and ballistic. The description of the wall velocity in these limits is significantly simplified compared to conventional methods, which allows for the derivation of analytic formulas valid for slow walls. As an example, I will apply this new approach to the QCD phase transition, which can be made first-order with a large baryon chemical potential. Using these bounds on the wall velocity, I will show that previous studies greatly overestimated the amplitude of GWs produced by assuming luminal wall speeds.

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

Bounds_on_bubble_wall_velocity.pdf

Recording

15:00 Coffee break

Intermediate scales: Short talks

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intermediate scales:
https://www.menti.com/al7v358nsur8
6832 1667

Convener: Jorinde van de Vis (CERN)

discussion_intermediate_scales_results.pdf

15 Examples of GW from FOPT and WallGo

Examples of GW from FOPT in BSM models and WallGo: I present three examples of BSM producing GW: one from SO(10) from the breaking chain $SU(3)_C\times SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ (2506.07182), another from a first-order phase transition of the inflaton coupled to a dark sector (2412.17278) and the third one from reheating through particle production. As we know, uncertainties in the fundamental parameters affect the phase transition observables. I will present how predictions drastically change in these scenarios taking into account these uncertainties. I will present some results using WallGo and the limitations we have found using it.

Speaker: Liliana Velasco-Sevilla (Sogang University, South Korea)

gw_wg_seminar_velasco_sevilla.pdf

Recording

16 Bubble wall velocity from hydrodynamics

Terminal velocity of bubble walls in cosmological first-order phase transitions is a key parameter affecting both the primordial gravitational wave signal and baryon asymmetry production in electroweak baryogenesis. In this talk, I present recent results showing that, under local thermal equilibrium, pure hydrodynamic backreaction can lead to steady-state expansion, as confirmed by numerical simulations. However, this is not generic. Runaways are more common, as bubble walls often reach supersonic velocities before the fluid shell forms. To capture this effect, we extend analytical methods beyond local equilibrium and provide a criterion to identify physical detonations, with important consequences for cosmological observables.

Speaker: Mateusz Zych (University of Warsaw)

CERN2025.pdf

Recording

Microscopic scales

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microscopic scales:
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2830 8284

Convener: Jorinde van de Vis (CERN)

discussion_microscopic_scales_results.pdf

17 Limits of EFTs at finite temperature for strong phase transitions

Phase transitions are violent and interesting phenomena that could have occurred in the early universe. Possible techniques to study these phenomena can be used in the presence of a hierarchy of scales, leading to the construction of finite temperature Effective Field Theories by integrating out heavier scales. These EFTs are reliable when the dynamics are mainly encoded in the most relevant operators. I will discuss the limits of such EFTs, showing how higher-dimensional operators affect the prediction of stronger transitions, including those detectable by LISA. These considerations impact the applicability of effective theory techniques, including their use in lattice studies.

Speaker: Fabio Bernardo

Limits_of_EFTS_for_strong_phase_transitions_Fabio_Bernardo.pdf

Recording

Intermediate scales: Panel Discussion

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intermediate scales:
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6832 1667

Convener: Jorinde van de Vis (CERN)

discussion_intermediate_scales_results.pdf

Wednesday 27 August

Intermediate scales: Morning session

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intermediate scales:
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6832 1667

Convener: Chiara Caprini (CERN)

discussion_intermediate_scales_results.pdf

18 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)

Branchina_CERN.pdf

Recording

Video preview

10:00 Coffee break

Intermediate scales: Morning session

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intermediate scales:
https://www.menti.com/al7v358nsur8
6832 1667

Convener: Chiara Caprini (CERN)

discussion_intermediate_scales_results.pdf

19 Strong cosmological phase transitions and their gravitational wave signals

We are currently witnessing the dawn of a new era in astrophysics and cosmology, started by the LIGO/Virgo observations of Gravitational Waves (GWs). Recently, also the detection of a stochastic background of GWs at very low frequencies was announced by the Pulsar Timing Array collaborations. In this talk, I will discuss terminal velocities reached by expanding bubble walls and the GW signals produced in very strong cosmological phase transitions .

Speaker: Marek Lewicki (University of Warsaw)

2025_8_PTGW_CERN_MLewicki.pdf

Recording

Video preview

20 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)

From_L_to_GW.pdf

Recording

Video preview

21 Group picture

12:10 Lunch break

Special contribution: TH Colloquium

Convener: Jorinde van de Vis (CERN)

22 Theory colloquium: New physics with the gravitational waves form early universe phase transitions

In many BSM physics scenarios the early Universe went through a first-order phase transition. The gravitational waves produced in the transition may be observable in future gravitational wave detectors, such as the LISA gravitational wave space mission. In order to fully utilize the observations the gravitational wave production must be calculated to high precision. In this talk I discuss the importance of numerical simulations in the analysis of phase transitions, from BSM thermodynamics, critical bubble nucleation and the subsequent hydrodynamic evolution and gravitational wave production.

Please check the event on : https://indico.cern.ch/event/1505527/

Speaker: Kari Rummukainen

cern25.pdf

Recording

Recording

Video preview

18:30 Social dinner

Thursday 28 August

Macroscopic scales: Morning session

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7220 6604

Convener: Hyun Min Lee

discussion_macroscopic_scales_results.pdf

23 Strong phase transitions and gravitational waves

Speaker: Thomas Konstandin

animation_strong_32 (1).mp4

Recording

seminar.pdf

10:00 Coffee break

Macroscopic scales: Morning session

join the discussion poll:

https://www.mentimeter.com/app/presentation/aluyxxy6p6qytfrn53ixqttuxzu29pk9/edit?source=share-modal
7220 6604

Convener: Hyun Min Lee

discussion_macroscopic_scales_results.pdf

24 Pulsar Timing Arrays Data in the View of Early Universe Physics

Recent detection of stochastic gravitational wave background by pulsar timing arrays (PTAs) missions opens a new window of testing fundamental physics laws at energy scales far beyond what is reached by particle physics experiments and/or by astrophysical observations; In my talks I will addresses such early-universe sources as primordial hydro and magnetic turbulence which are possibly present at the the epoch of the QCD phase transition Additionally I will discuss the PTAs data in the context of massive gravity independently of the gravitational wave signal origin (astrophysical or cosmological).

Speaker: Tina Kakhniashvili

GENEVA-2025.pdf

GENEVA-2025.pdf

GENEVA-2025.pptx

Recording

25 Acoustic fluid perturbations in first-order phase transitions

We study the irrotational velocity spectra induced in a fluid during a first-order phase transition in the radiation-dominated era. Interactions of the scalar broken-phase bubbles with the fluid generate irrotational velocity and enthalpy profiles which are, together with the statistical time distribution of bubble nucleation and collision, predictive of the gravitational wave spectrum produced in the sound-wave phase after bubble collisions. The main result we present is a refined template for the spectrum of the initial fluid perturbations in the acoustic phase in terms of phase transition parameters, showing how its amplitude and spectral shape can be reconstructed from the scales that appear in the single-bubble perturbations.

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

Midiri CERN.pdf

Recording

12:00 Lunch break

Macroscopic scales: Afternoon session

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7220 6604

Convener: Simona Procacci (University of Geneva (CH))

discussion_macroscopic_scales_results.pdf

26 Cosmological first-order phase transitions with large bubbles: beyond conformal fluid and flat spacetime

Using semi-analytical models, we investigate the power spectrum of gravitational waves generated by sound waves in the plasma during a first-order phase transition in new unexplored scenarios. (i) The phase transition is accompanied by a change of the equation of state from that of pure radiation. This causes the peak of the spectrum to shift to smaller frequencies as the equation of state becomes softer and suppresses the amplitude of the power spectrum as a consequence of both sound and gravitational waves propagating across a non-conformal fluid.
(ii) In addition, we investigate the novel limit of large bubbles, by which we mean that the mean bubble spacing $R_*$ is a non-negligible fraction of the Hubble length $\mathcal{H}_*^{-1}$, i.e. $R_*\mathcal{H}_* \lesssim \mathcal{O}(1)$. Since the amplitude of the gravitational wave
signal increases with $R_*\mathcal{H}_*$, this is also the loud signal regime. In this regime the effects of gravity, hitherto neglected, become relevant. We carry out the calculation in cosmological perturbation theory expanding in the parameter $R_*\mathcal{H}_*$, or bubble over Hubble radius.
General relativistic contributions at the next-to-leading order suppress the gravitational wave peak amplitude, with respect to the leading order contribution, by an amount that scales as $(R_*\mathcal{H}_*)^2$ and also depends on other transition parameters.
This work improves the current estimation of the gravitational waves power spectrum
from first order phase transitions and expands the possible scenarios of transitions that can
be tested by gravitational wave detectors.

Speaker: Lorenzo Giombi (University of Helsinki)

LG_presentation_CERN.pdf

Recording

27 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

slides.pdf

15:00 Coffee break

Macroscopic scales: Short talks

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https://www.mentimeter.com/app/presentation/aluyxxy6p6qytfrn53ixqttuxzu29pk9/edit?source=share-modal
7220 6604

Convener: Alberto Roper Pol

discussion_macroscopic_scales_results.pdf

28 Exploring Parameter Dependence in the Double-Broken Power Law for GW Signals

The gravitational wave spectrum from sound wave contributions is typically modeled as a double-broken power law with fixed spectral slopes. However, the intermediate slope depends on phase transition parameters, which can help resolve degeneracies when reconstructing these parameters. To improve gravitational wave predictions, we provide an analytic form of this parameter dependence, derived via approximations or numerical fits, based on the sound shell model.

Speaker: Eric Madge Pimentel (IFT-UAM/CSIC)

Madge-CERN.pdf

Recording

29 The complicated story of Primordial Black Holes production in cosmological Phase Transitions

In this talk, I will investigate the formation of Primordial Black Holes as the result of the collapse of energy density fluctuations originating from supercooled first-order phase transitions. I will present the results of a simplified approach, where the energy density fluctuations are evolved within the limit of flat FRW Universe. I will show how energy density fluctuations modify the Gravitational Wave signals as the production of secondary Gravitational Waves is induced. Finally, we will discuss the full covariant formalism of cosmological perturbation and show how it impacts the production of Primordial Black Holes and Gravitational Waves.

Speaker: Piotr Toczek (University of Warsaw)

PiotrToczek_CERN.pdf

Recording

30 From equations of state to gravitational wave spectra

The Sound Shell Model provides a computationally efficient way of calculating the gravitational wave spectra of cosmological first-order phase transitions. Based on the Sound Shell Model, we have created the simulation framework PTtools and integrated it with our web-based plotting utility PTPlot.

In this talk I will show how to use PTtools and PTPlot to easily compute Sound Shell Model power spectra for arbitrary equations of state. This is crucial to improving the quality of predictions of stochastic backgrounds of gravitational waves from phase transitions, including equations of state beyond the bag model with temperature- and phase-dependent sound speeds.

Speaker: Mika Mäki

Recording

Slides

31 Gravitational wave production: the interplay between vortical and compressional motions

In the early Universe, during a phase transition, the surrounding plasma is subjected to a fluid motion sourcing gravitational waves. This fluid motion can be composed of compressional and vortical motions. Most of the time, they are considered distinct and studied independently. However, by analyzing the UETC of the anisotropic stresses, a mixed term combining vortical and compressional motions leads to another contribution to gravitational wave production.
In this presentation, the interplay between the two motions will be at the heart of the discussion.

Speaker: Madeline Clara Salome (Universite de Geneve (CH))

GWs-CERN_Madeline_SALOME.pdf

Recording

32 GW fingerprints of inverse FOPTs

Building upon the recently proposed concept of inverse FOPT, we investigate their GW signatures. We outline how these transitions differ thermodynamically and hydrodynamically from standard ones and analyse the resulting GW emission from the plasma.

Adopting the bag equation of state as a minimal setup, we compute self-similar fluid profiles over a range of wall velocities and transition strengths. We evaluate the GW spectrum from sound waves via the Sound Shell Model, and compare it to analytic fits.

This analysis allows us to probe whether inverse transitions produce distinguishable spectral features, assess their observability with future detectors like LISA.

Speaker: Giulio Barni

GW_from_Inverse_PT_CERN_Giulio_Barni.pdf

Recording

Macroscopic scales: Panel Discussion

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7220 6604

Convener: Alberto Roper Pol

discussion_macroscopic_scales_results.pdf

Friday 29 August

Macroscopic scales: Morning session

join the discussion poll:

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7220 6604

Convener: Seong Chan Park

discussion_macroscopic_scales_results.pdf

33 Curvature perturbation from first-order phase transitions & A positive-definite formulation of tunneling

This talk is consists of two parts. In the first part I will talk about curvature perturbation produced in very strong first-order phase transitions. I will first explain super-hubble curvature perturbation based on 2311.16222, and then move on to hubble-scale curvature perturbation based on 2503.01962. In the second part I change the topic and talk about a new type of formulation of quantum tunneling that features positive-definite action based on an ongoing work.

Speaker: Ryusuke Jinno (Kobe University)

Jinno.key

Jinno.pdf

Recording

10:00 Coffee break

Special contribution: Final overview

Convener: Chiara Caprini (CERN)

34 Gravitational waves from first order phase transitions: progress and problems

I review calculations of gravitational waves from the fluid flows generated by first order phase transition in the early universe, summarise the current status in simulations and modelling, and suggest areas where further progress can be made in preparation for the LISA mission.

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

G-Waves 2025 08 CERN.pdf

Recording

35 Discussion

Speaker: Chiara Caprini (CERN)

discussion_PT_week_CERN.pdf

Recording