Organisation des séminaires et calendrier

Résumé: In critical limits of statistical models, non-local observables such as cluster connectivities can be conformally invariant without necessarily belonging to a conformal field theory. We propose to describe such observables in terms of conformal correlator systems, defined by weaker axioms than those of CFT. In particular, N-point functions can be reduced to 4-point functions, instead of 3-point functions in CFT.

In two dimensions, the spectrum of a conformal correlator system is not constrained by modular invariance. This allows the spin to take arbitrary complex values, leading to correlators with nontrivial monodromies. We show that sphere 4-point functions and torus 1-point functions are subject to nontrivial monodromy constraints. We give examples of correlators with abelian monodromies: explicit examples from free fields, and more complicated examples from critical loop models.

Intervenante: Angèle Lochet

Nous expliquerons pas à pas comment les caractéristiques physiques d’un trou noir ont mené à un paradoxe, appelé paradoxe de l’information. Notamment, nous mettrons l’accent sur ce que nous appelons information, qui est souvent source d’incompréhension. Si le temps le permet, nous verrons des pistes de résolution de ce paradoxe.

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Abstract: This talk explores scattering processes into final states containing a large number of particles, \((n \gg 1)\), in a four-dimensional massive scalar quantum field theory. I will begin by reviewing known results for tree-level and loop-level amplitudes at and near the multi-particle mass threshold in the limit \((\lambda \to 0)\) with \((n \sim E/m \to \infty)\). Since such high-multiplicity processes ultimately require a non-perturbative treatment, I will then present a semiclassical calculation valid in the weak-coupling, large-multiplicity regime with \((\lambda n \gg 1)\). We will discuss the apparent explosive growth of partial decay widths of highly virtual particles near (n)-particle thresholds, the interplay between the Higgsplosion and Higgspersion mechanisms, and the consistency of these phenomena with the unitarity of the theory.

Abstract: 

There is an intriguing robustness in certain statistical patterns describing the dynamics and organization of seemingly very different ecosystems, spanning scales from trees in a rainforest to bacteria in the human gut.

These patterns motivate several common questions: How can so many ecologically similar species coexist locally? Why does only a small fraction of these coexisting species typically account for most of the total biomass? What drives changes in the identity of these dominant species across space and time?

In this lecture, I will give an account of recent work at the intersection of statistical physics and theoretical ecology that aims to address these questions. Emphasis will be placed on disordered-systems approaches, which provide a natural theoretical framework without committing to any specific ecosystem.

Topics covered include:

• Common patterns in the organization and dynamics of species-rich ecosystems
• Disordered Lotka-Volterra-like models and Dynamical Mean-Field Theory
• Models for the coexistence of spatially extended populations
• Inverse stability-complexity relationship in the presence of environmental disorder

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After describing elastic interactions and the discovery of the odderon by the TOTEM and D0 Collaborations, we will discuss new kinematical regimes where the gluon density in the proton or Pb can be very large which leads to new equations in Quantum Chromodynamics.  We will also present the latest expectations on beyond standard model physics and especially the production of axion-like particles using intact protons after the collision.  We will finish by describing briefly the Low Gain Avalanche Detectors and their applications in medicine for cancer treatment and with NASA to measure cosmic rays.