Electron-Monopole Scattering from Conformal Field Theory

• Clay Córdova (University of Chicago)

Room: Centre de conférences Marilyn et James Simons S-wave scattering of electrons off of heavy magnetic monopoles is an important problem both in formal theory and in particle phenomenology. It has long been understood that this scattering can be effectively studied in two-dimensional conformal field theory with a recently appreciated crucial role played by topological line defects and generalized global symmetry. We use the formalism of boundary CFT to compute the S-matrix to leading order in electromagnetic coupling and find agreement with expectations from unitarity.

Discussion: "Monopoles, Strings, etc."

• Daniel Brennan (University of Birmingham)
• Sungwoo Hong (KAIST)

Room: Centre de conférences Marilyn et James Simons

Free discussion Room: Centre de conférences Marilyn et James Simons

Abelian Instantons in Quantum Field Theory and Gravity

• Isabel García García (University of Washington)

Room: Centre de conférences Marilyn et James Simons

Dynamics of the Fermion-Rotor System

• Vazha Loladze (University of Oxford)

Room: Centre de conférences Marilyn et James Simons In this talk, I will examine the dynamics of the fermion–rotor system, originally introduced by Polchinski as a toy model for monopole–fermion scattering. Despite its simplicity, the system is surprisingly subtle, with ingoing and outgoing fermion fields carrying different quantum numbers. I will show that the rotor acts as a twist operator in the low-energy theory, changing the quantum numbers of excitations that have previously passed through the origin to ensure scattering consistent with all symmetries, thereby resolving the long-standing Unitarity puzzle. I will then discuss generalizations of this setup with multiple rotors and unequal charges, and demonstrate how the system can be viewed as a UV-completion of boundary states for chiral theories, establishing a connection to the boundary conformal field theory based proposal for resolving the puzzle.

Discussion "Generalized Symmetries: Useful for Model Building?"

• Nathaniel Craig (UC Santa Barbara)
• Ben Gripaios (Cambridge University)

Room: Centre de conférences Marilyn et James Simons

2d Dualities and Mass Hierarchies

• Raffaele Tito D'Agnolo (IPhT, CEA Saclay/ENS)

Room: Centre de conférences Marilyn et James Simons I will explore the Kramers-Wannier duality in the continuum and comment on its implications for the electroweak hierarchy problem.

Free discussion Room: Centre de conférences Marilyn et James Simons

QCD Wilson Lines in IR Chiral Lagrangian (Remote)

• Ho Tat Lam (Stanford University)

Room: Centre de conférences Marilyn et James Simons In this talk, we will answer the question: What does a QCD Wilson line flow to in the IR chiral Lagrangian? We will first present a symmetry-based argument showing that the Wilson line is not completely screened in the IR. We then propose a disorder operator realization of the Wilson line in the chiral Lagrangian. This allows us to model heavy-light mesons and baryons and describe the dissolution of confining strings into pions within the chiral Lagrangian.

Spurion Analysis for a Class of Selection Rules Without Group Actions

• Ling-Xiao Xu (ICTP)

Room: Centre de conférences Marilyn et James Simons Recent advances have uncovered a new class of selection rules in particle physics models arising from non-invertible fusion algebras. We refer to these as non-invertible selection rules (NISRs), distinguishing them from conventional selection rules derived from ordinary group laws. In this talk, we illustrate their implications in perturbation theory using spurion analysis, and connect to aspects of "loop-induced groupification" and particle decoupling in effective field theories. The discussion is based on arXiv 2510.18972, 2508.14970, 2503.19964.

Discussion: "The S-Matrix, Generalized"

• Diego García-Sepúlveda (Harvard University)
• Lucia Córdova (University of Amsterdam)

Room: Centre de conférences Marilyn et James Simons

Free discussion Room: Centre de conférences Marilyn et James Simons

Student talks

• Jonah Berean-Dutcher (UBC & IHES)
• Finn Gagliano (Durham University)
• Marius Kongsore (NYU)

Room: Centre de conférences Marilyn et James Simons

Berry Phase on Boundary Conformal Manifolds

• Yichul Choi (Institute for Advanced Study)

Room: Centre de conférences Marilyn et James Simons Conformal boundary conditions appear in various different contexts, in the study of impurities, scattering of massless particles off a heavy monopole, D-branes, and so on. I will discuss a new “higher” geometric structure the space of conformal boundary conditions possesses in 1+1d conformal field theories.

Discussion: "The Global SM & Beyond"

• Seth Koren (University of Notre Dame)
• Po-Shen Hsin (King's College London)

Room: Centre de conférences Marilyn et James Simons

Testing Stringy and Field Theory GUTs With Axions

• Mario Reig (CERN)

Room: Centre de conférences Marilyn et James Simons The topological nature of axion couplings to gauge bosons offers unique opportunities to obtain information about the UV limit of the SM. The coupling to photons is particularly important experimentally. I will discuss why the discovery of an axion-like particle above the QCD line would rule out grand unified theories, the perturbative heterotic string, and F-theory GUTs. Based on 2206.07053, 2410.03820 and 2509.08042.

Free discussion Room: Centre de conférences Marilyn et James Simons