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Aaron Held (École Normale Supérieure)10/21/26, 9:30 AM
The Standard Model of particle physics, in particular the Higgs potential, exhibits hints of fundamental quantum scale symmetry. At the same time, the asymptotic safety program has gathered substantial evidence for a nonperturbative fixed point of gravitational interactions. If this gravitational fixed point induces a UV completion of the Standard Model, it offers a compelling explanation for...
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Manuel Reichert (University of Sussex)10/21/26, 10:15 AM
The functional renormalisation group is a powerful non-perturbative tool for the computation of the vacuum and finite-temperature effective potential. It is automatically IR-finite and includes the resummation of bubble diagrams, similar to Daisy and super-Daisy resummations in perturbation theory. I will introduce this tool and, as an example, show its application to the electroweak phase...
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Pedro Tarancón-Álvarez (Institute of Cosmos Sciences - University of Barcelona (ICCUB))10/21/26, 3:00 PM
The hydrodynamics of expanding bubbles is a key ingredient in the prediction of gravitational waves from cosmological first-order phase transitions. It fixes which expansion types are possible, and it provides a proxy for how much energy is available for gravitational wave emission. These predictions normally rely on a conformal equation of state, which need not hold in strongly coupled or...
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Anish Ghoshal (University of Sussex, UK)10/21/26, 3:20 PM
Collisions of ultra-relativistic bubbles during cosmological phase transitions can produce particles much heavier than the transition scale. Previous analyses modelled this process as the off-shell decay of the scalar background. We show that its results parametrically overestimate hard particle production and depend on the gauge choice and the coordinate choice in field space. We propose an...
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Henda Mansour (KIT)10/21/26, 3:40 PM
When reheating is delayed, supercooled first-order phase transitions are often assumed to hand the Universe over to an early era of matter domination. In this talk I ask whether this assumption actually holds, and argue that it generally does not — at least not immediately. Bubble collisions leave behind a highly inhomogeneous scalar field with persistent relativistic gradients, producing an...
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Andrzej Wereszczyński (Jagiellonian University, Kraków, Poland)10/21/26, 4:00 PM
I show that the inclusion of a dimension-six operator in the Higgs potential has a dramatic impact on the stability of oscillons in the SU(2) bosonic sector of the Standard Model, extending their lifetime by orders of magnitude. This happens for the physical value of the ratio between the Higgs and W boson masses, mH /mW = 1.556 and for the dimension-six operator (Φ^†Φ)3 whose coupling...
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Eduardo Peinado (Instituto de Física de la Universidad Nacional Autónoma de México)10/21/26, 5:00 PM
$U(1)_{B-L}$ gauged extensions of the Standard Model provide a simple and phenomenological rich framework for neutrino mass generation. However, dark matter and the stability of the Higgs potential are often addressed as separate issues. In this talk, we discuss a model in which these three aspects are linked. The model contains two sterile pseudo-Dirac fermion pairs in the visible sector and...
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Moritz Bosse (TU Dortmund)10/21/26, 5:20 PM
It is widely appreciated that the electroweak vacuum of Standard Model
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resides in a region of metastability. We discuss how absolute stability is
achieved in extensions by a real scalar singlet. Using the renormalisation
group running of couplings, we identify the parameter region for stability
up to the Planck scale, mediated by the Higgs-portal interaction.
Higgs-singlet mixing connects... -
Giorgio Laverda (JGU Mainz)10/21/26, 5:40 PM
The Higgs non-minimal coupling to background curvature is well known to stabilise Higgs fluctuations during inflation, thus alleviating the vacuum-stability problem. However, during a post-inflationary phase of kination, the same coupling can generate a large tachyonic effective mass, dramatically worsening the stability of the Higgs vacuum. In this talk, I will show how this tachyonic...
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Giulio Barni (IFT-UAM/CSIC Madrid)10/22/26, 10:15 AM
Semiclassical tunneling is usually formulated in Euclidean time, but for non-trivial initial states the appropriate Euclidean saddle and boundary conditions are not always obvious. I will introduce real-time path-integral approaches to tunneling, focusing on the steadyon construction based on complex semiclassical saddles, and use it to clarify how conserved quantities are incorporated.
I...
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Miguel Etienne A Vanvlasselaer (ICCUB)10/22/26, 11:40 AM
First-order phase transitions in the early Universe are pivotal for gravitational wave production, baryogenesis, and dark matter generation. A central question is whether bubble walls reach a subjouguet or ultra-relativistic velocity - a distinction governed by hydrodynamic obstruction, where plasma heating counteracts the vacuum pressure driving the wall. Traditional analyses assume...
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Anna Kormu (University of Helsinki)10/22/26, 12:00 PM
Nucleation rate computations are of broad importance in many aspects of physics, especially in the accurate estimation of the phase transition (PT) parameters that enter the gravitational wave (GW) power spectrum. The nucleation rate and PT parameters rely on perturbative estimates. Therefore, they are dependent on the details of the semiclassical picture and different orders of perturbative...
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Alex Jenkins (University of Cambridge)10/22/26, 12:20 PM
False vacuum decay plays a pivotal role in the physics of the early Universe. However, we lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on untested assumptions and approximations. In this talk, I will introduce two complementary approaches toward a real-time theory of vacuum decay: semiclassical...
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Dr Oliver Janssen (EPFL)10/22/26, 12:40 PM
We review a method to compute semiclassical time evolution in quantum mechanics via the path integral, illustrating how it works in paradigmatic examples. This includes the decay of general, excited metastable states from a false vacuum, generalizing a method due to Coleman for the would-be ground state. We then apply the method to compute the time-dependent decay rate of a particle that is...
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Satumaaria Sukuvaara (University of Helsinki)10/22/26, 3:00 PM
While cooling down, the early universe is believed to have undergone symmetry breaking phase transitions. One attractive possibility for extending the Standard Model is that these phase transitions are of the first order, as they might be able to produce observable gravitational waves. We consider a dark matter freeze-out mechanism, filtering, where dark matter particles become massive in a...
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Nadir Ijaz (University of Padova, Italy)10/22/26, 3:20 PM
A rolling axion inflaton can amplify one polarization of a gauge field through its pseudoscalar coupling. The amplified fields source scalar fluctuations and gravitational waves, and their backreaction can substantially change the inflaton’s motion. In this talk, I will present our numerical study of this coupled evolution and discuss when the homogeneous-backreaction approximation remains...
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Carlo Tasillo (IFIC, Valencia University)10/22/26, 3:40 PM
A first-order electroweak phase transition in the CP-conserving type-I two-Higgs-doublet model can source a gravitational wave background in the LISA band. From extensive Monte Carlo scans over the collider-viable parameter space, we find that LISA-detectable signals arise almost exclusively where observable deviations at the HL-LHC are predicted, in particular in the H → ZZ channel for a...
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Oliver Gould (University of Nottingham)10/22/26, 4:00 PM
The critical, universal behaviour of any second-order phase transition gives rise to stochastic anisotropic stresses. These in turn source a stochastic spectrum of gravitational waves. In this talk, I show how to derive the rate of gravitational wave production for second-order phase transitions in the simplest dynamical universality class, Model A, describing a diffusive scalar order...
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Fabio Bernardo (Université de Genève)10/22/26, 5:00 PM
Phase transitions are violent and fascinating phenomena that may have occurred in the early Universe. When a hierarchy of scales is present, they can be studied using finite-temperature Effective Field Theories, obtained by integrating out the heavier degrees of freedom. Such EFTs provide a reliable description as long as the dynamics are dominated by the most relevant operators. In this talk,...
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Javier López Miras (Universidad de Granada)10/22/26, 5:20 PM
The high-temperature effective field theory (3D EFT) approach to phase transitions relies on the assumption of a power counting which organizes the EFT expansion. Most studies truncate such expansions at superrenormalizable level, yet there is increasing evidence of the relevance of higher-dimensional corrections in the strong transition regime. A consistent treatment of such corrections,...
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Luis Gil (Universidad de Granada)10/22/26, 5:40 PM
In this talk I will discuss our recent advancements, and the technical challenges involved, in the precise determination of the high-temperature limit of the Standard Model Effective Field Theory (SMEFT). Through a comparison with lattice data, we provide evidence that the SMEFT may undergo a first-order phase transition even in the absence of direct modifications of the Higgs potential. In...
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David Weir (University of Helsinki)10/23/26, 10:15 AM
A leading candidate for a stochastic source of primordial gravitational waves would be a first order phase transition. Strong electroweak-scale phase transitions in particular stand a good chance of being constrained by gravitational wave data from future missions such as LISA and Taiji, and thus it is important to understand the signal from strong transitions. However, strong transitions also...
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Alberto García Martín-Caro (Universidades de Vigo)10/23/26, 12:25 PM
Cosmic strings arise naturally in theories with spontaneously broken symmetries and can carry important information about the dynamics of phase transitions in the early Universe. In this talk I will present a systematic framework for deriving the effective action governing the Goldstone degrees of freedom associated with the breaking of spacetime symmetries by string defects, together with...
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Maximilian Bachmaier (University of the Basque Country)10/23/26, 12:45 PM
The Standard Model of particle physics provides a good approximation at low energy scales. In the early hot universe, however, it is assumed that there was a so-called grand unified theory, which unified the three fundamental forces of particle physics. However, all attempts to unify these three forces lead to a possible overabundance of ’t Hooft–Polyakov magnetic monopoles. But why magnetic...
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