Not so minimal warm inflation

• Mar Bastero-Gil (University of Granada)

Room: V12M An axion-like inflaton coupled to non-Abelian gauge bosons provides a compelling microphysical framework for warm inflation. Starting even from cold initial conditions, in these systems, sphaleron heating may generate thermal friction sufficient to sustain finite temperatures throughout the inflationary epoch. Insisting on shift-symmetric potentials, we revisit the viability of these scenarios under the designation of Minimal Warm Inflation. We examine both observational constraints and model-building limitations on models with a hierarchy between the decay constants appearing in the friction rate and in the inflaton potential. We conclude that the popular clockwork mechanism cannot generate the required hierarchy; however, partial-wave unitarity bounds admit effective descriptions that remain consistent with observations.

Non-conformal obstructions to bubble expansion

• Pedro Tarancón Álvarez (ICCUB)

Room: V12M 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 QCD-like sectors. In this talk, I will relax this assumption and study the self-similar bubble solutions for a family of equations of state that interpolates between electroweak-like and QCD-like transitions. Non-conformality turns out to obstruct bubble expansion, ruling out otherwise admissible solutions and, at the same time, enabling a new expansion mode. I will discuss how both effects reshape the space of solutions and the kinetic energy fraction. If time permits, I will discuss how the collision of bubbles in a QCD-like phase transition leads to a phase-separated final state rather than a homogeneous one.

Domain walls are singular

• Oriol Pujolas (IFAE)

Room: V12M Cosmological domain walls (DWs) are a powerful probe of spontaneously broken discrete symmetries, which occur in a number of well-motivated new physics scenarios. At the same time, DW networks pose a significant computational challenge: their main observational signatures (GWs, PBHs) are generated during the violent epoch of network collapse, which requires large-scale numerical simulations. Studying instead the collapse of individual closed walls is revealing: DWs generically develop worldvolume singularities, much like cusps on cosmic strings. These singularities can be line-like (“cuspidal edges”) or point-like (“cuspidal vertices”), and they follow the universal patterns of singularity theory. They appear both in the thin-wall (Nambu-Goto) description and in full field theory simulations. I will discuss some of their phenomenological implications.

Quantum dynamics and response of near-extremal black holes

• Stefano Trezzi (ICCUB)

Room: V12M It has recently been understood that the near-horizon geometry of near-extremal black holes undergoes large quantum fluctuations, signaling a breakdown of semiclassical gravity. Remarkably, these large quantum gravity effects are controllable and occur at curvatures far below the Planck scale. I will show how these quantum fluctuations drastically modify the dynamics and response of near-extremal black holes. Sufficiently cold black holes become transparent to electromagnetic and gravitational radiation of fixed helicity below a frequency threshold set by a spin-induced energy gap. The same gap modifies the Danielson–Satishchandran–Wald decoherence effect: near-extremal black holes can fail to decohere spatial superpositions at late times. Quantum fluctuations also make these black holes deformable, generating nonzero Love numbers, and modify their quasinormal-mode spectrum and late-time response, with implications for the classical Aretakis instability.

Simulation-Based Inference for Weak Lensing: From Stage III to Stage IV Surveys

• Marco Gatti (ICE-CSIC)

Room: V12M Simulation-based inference (SBI) and higher-order statistics have emerged as powerful tools for extracting substantially more cosmological information from large-scale structure probes than standard two-point analyses. Implementing them requires a genuinely multidisciplinary approach. It combines high-performance computing (large suites of N-body simulations and data-intensive workflows), detailed physical and observational modelling (baryonic feedback, intrinsic alignments, and survey systematics), and statistical and machine-learning methods tailored to these frameworks, such as data compression and neural likelihood estimation. Although these methods are relatively recent, they have now reached maturity in weak-lensing analyses. In this talk, I will review the current state of the art, focusing on Stage III results from DECam data covering nearly 15,000 deg² of the sky. I will then discuss the transition to Stage IV surveys, highlighting both the opportunities and the key challenges that must be addressed to realise the full potential of SBI in the next generation of cosmological analyses.

General Spin-1 Cosmological Collider Signals

• Carlos Duaso Pueyo (Scuola Normale Superiore, Pisa)

Room: V12M The cosmological collider program attempts to characterise and compute the signatures left by particles present during inflation on cosmological correlation functions. In most of the existing literature, such particles are described as irreps of the de Sitter (dS) isometry group with fully covariant free Lagrangians. Inflation, however, spontaneously breaks some of these symmetries, so going beyond the dS assumption is important for obtaining sharper signal templates and maximising the chances of detection. In this talk I’ll construct the most general free theory of a massive spin-1 field during inflation using only the unbroken symmetries, Bunch-Davies conditions, and the requirement of microcausality. Then I will couple this general spin-1 field to the inflationary perturbations and describe its imprints on cosmological correlators, focusing on how observations might allow us to distinguish it from the dS-invariant setup. Finally, I will comment on the extension to higher spins.