Organisation des séminaires et calendrier

Abstract:
Characterising the average (and typical) ground-state energy (GSE) of mean-field disordered systems (or free energy at positive temperature) has been the focus of a large body of literature first in physics (e.g. via replica computations) and then rigorously in mathematics (e.g. via cavity, interpolation methods) in the past 40 years. This observable is generally expressed through a Parisi formula, i.e. an optimisation problem over a set of overlap probability distribution. In comparison, much less is known about the fluctuations of the GSE. In a recent series of work, I have derived an explicit expression for the large deviation function (LDF), characterising atypical fluctuations of the GSE, for spherical and Ising spin-glasses as well as for the elastic manifold. In this talk I will focus on the former. Interestingly, the expression for the LDF is again an optimisation problem over a skewed probability distribution function, allowing to characterise which configurations lead to an atypical fluctuation. The LDF generically displays a rich phase diagram with different patterns of replica-symmetry breaking. Most interestingly, I will show that the behaviour of the LDF in the vicinity of the average and typical GSE is universal and allows to make precise predictions on the non-trivial tails of the distribution of typical fluctuations of the GSE.
This talk is based on an article (J. Stat. Phys. 191 (2), 11 (2024) / arXiv preprint arXiv:2306.11927) in collaboration with Y.V. Fyodorov (King’s College London) and P. Le Doussal (LPENS).

An energetic parton crossing a hot or dense quark-gluon plasma (QGP) can lose energy through elastic collisions with the medium, a process contributing to jet and hadron suppression observed in heavy-ion and recently also in light-ion collisions. Going beyond existing approaches, which mostly focus on the average energy loss per unit distance for large systems, we derive the full energy loss probability distribution (or quenching weight) from first principles using Landau’s kinetic equation to resum the energy losses suffered in
multiple successive elastic scatterings. The distribution captures rare but significant fluctuations, arising from the long tail of the single scattering spectrum, and includes the possibility of energy gain from the medium, both effects being especially relevant for small
systems. Our results fill a conceptual gap in the modelling of jet/hadron and heavy flavour suppression, where usually only those fluctuations of the radiative energy loss are taken into account, and may help interpret high-multiplicity pp and pA data.

The SU(2) Wess-Zumino-Witten model is one of the best understood 2d conformal field theory. In this talk, I will discuss its integrable structure. In particular, I will give evidence for the existence of an infinite number of commuting higher-spin local charges built from the current algebra underlying this CFT. In the second half of the talk, I will discuss the diagonalisation of these commuting operators on the Hilbert space of the theory, formed by highest-weight representations of the current algebra. In particular, I will review a conjecture relating the spectrum of these operators to the properties of specific ODEs (within the so-called ODE/IM correspondence). This talk is based on 2601.20960, in collaboration with Adrien Molines.

TBA

We study the long-time, large-distance asymptotic behaviour of dynamical two-point correlation functions of the Lieb–Liniger model in the limit of infinite repulsion (the one-dimensional impenetrable Bose gas). Starting with exact representations of correlation functions in terms of Fredholm determinants of an integrable integral operator, we perform the rigorous asymptotic analysis, using Riemann–Hilbert techniques. The integral operator
depends parametrically on time \(t\), distance \(x\) and on the filling fraction — a function that characterizes the thermal or non-thermal equilibrium conditions. We consider a large class of non-thermal equilibrium conditions, extending previous results established for the thermal equilibrium case. The long-time and large-distance asymptotic behaviour is derived for two classes of filling fractions. These classes are characterized by the number of poles on the real axis (a generalization of Fermi points) that, together with the unique saddle point, contribute to the asymptotic expansion. For each class, we derive the long-time, large-distance symptotic behaviour as a series in \(x\)^\(−1/2\) as \(x\) and \(t\) go to infinity for a fixed ratio \(x/t\). We provide explicit closed-form expressions for the leading and sub-leading terms, logarithmic corrections, and overall constants in terms of special functions and simple integrals. For the impenetrable Bose gas in thermal equilibrium, we verify the derived asymptotic expansions by comparing them with the existing results in the literature and with numerical data.
This talk is based on joint work with Frank Göhmann, Karol K. Kozlowski, and Alexander Weiße.

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.

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.