| Wednesday 25 December 2024 | |
| Events for day: Wednesday 31 May 2023 |
| 13:30 - 15:00 Weekly Seminar (Online) Positivity Constraints on Lorentz-breaking EFTs https://www.skyroom.online/ch/soa/weekly-seminar School ASTRONOMY The coefficients of the operators of an effective field theory (EFT) are constrained to satisfy certain inequalities, under the (mild) assumption that the UV completion satisfies general requirements of causality and unitarity. We begin the extension of these ideas to theories where the Lorentz symmetry is spontaneously broken, as it happens in cosmology and condensed matter physics. Constraints are derived using dispersive arguments for the 2-point function of conserved currents and of the stress-energy tensor. To join the seminar, please click on the following link ... 16:00 - 17:00 Mathematics Colloquium Bootstrap Percolation on Graphs School MATHEMATICS We discuss two notions of percolation on graphs. The first one is $r$-neighbor bootstrap percolation in which an activation process of the vertices of a given graph is carried out. The process starts with some initially activated vertices and then, in each round, any inactive vertex with at least $r$ active neighbors becomes activated. The second one is the so called graph bootstrap percolation in which we activate the edges of a graph instead of vertices. Starting with some initially activated edges, we activate any inactive edge which creates a new copy of $H$, the pattern or base graph. Two problems, one of combinato ... 17:30 - 19:00 Number Theory Webinar Abelian Arboreal Representations School MATHEMATICS I will present joint work with Andrea Ferraguti which makes progress on a conjecture of Andrews and Petsche that classifies abelian dynamical Galois groups over number fields, in the unicritical case. I will explain how to reduce the conjecture to the post-critically finite case and the key tools to handle all unicritical PCF with periodic critical orbit over any number field and all PCF over quadratic number fields. Along the way I will present an earlier rigidity result of ours on the maximal closed subgroup of the automorphism group of a binary rooted tree, which offered us with the main input to translate the commutativity of the Galois i ... |