Events calendar

François Huveneers

Kings College London

Many-body localization (MBL) is an out-of-equilibrium phase of matter featuring emergent integrability: There exists a complete set of local integrals of motion. As a result, an MBL system remembers its initial state for arbitrarily long times if the system is thermally isolated. This implies, in particular, a total absence of transport. Demonstrating this with mathematical rigor proves highly challenging. In this talk, I will present a theorem stating that the diffusion constant of such systems vanishes, indicating that transport is at most sub-diffusive. An interesting aspect of the proof is that it relies on establishing MBL in some portions of the chains that are immune from resonances. Additionally, it rules out some numerical results that suggested MBL would not exist at all. Our work represents thus a step forward in rigorously establishing the existence of the MBL phase in one-dimensional systems. From a work with W. De Roeck, L. Giacomin and O. Prosniak.

Mario Reig (University of Oxford)

In this talk I will discuss axion couplings to gauge bosons in 4-dimensional Grand Unified Theories and in heterotic String Theory. The topological nature of these couplings allows them to be matched from the UV to the IR, and the ratio of the anomaly with photons and gluons for any axion is fixed by unification. I will show that this implies that there is a single axion — the QCD axion — with an anomalous coupling to photons. Other light axion-like particles can couple to photons by mixing with the QCD axion, and necessarily lie to the right of the QCD line prediction in the mass-coupling plane. As a result, the discovery of a single axion to the left of the QCD line can rule out simple GUTs and most of the studied heterotic string compactifications. (Based on: 2206.07053 and 2410.03820)

Interactions between species can lead to fluctuations in their population sizes. This is well understood in few-species communities, such as predator-prey systems, and explained in terms of dynamical models of interacting populations with few degrees of freedom. However, many natural ecosystems, from microbes in a grain of soil to plants in a rainforest, are home to a great variety of species. What kind of dynamical behavior should we then expect? I will present recent theoretical work using concepts from the physics of disordered systems to address this question. Connections to experiments will be discussed and similarities and key differences with other fields, such as glasses and neural networks, will be highlighted.

Benoît Assi (University of Cincinnati)

Tidal Love numbers quantify the finite-size properties of compact objects, such as absorption and their response to external fields. Perhaps surprisingly, even in classical general relativity, they undergo renormalization group running due to nonlinearities. In this talk I will explain some exact results about their running, which can be extracted using black-hole perturbation theory and point-particle effective theories (EFT). Due to the universality of the EFT, the results have applications to the physics of black holes, neutron stars, binaries and their signals in gravitational wave observatories. Our calculations can also provide the precise values of both static and dynamical Love numbers of black holes in various dimensions.

Jean-Daniel Bancal

TBA

TBA