Events at Physics |
Events During the Week of November 1st through November 7th, 2026
Monday, November 2nd, 2026
- Theory Seminar (High Energy/Cosmology)
- On Domain Walls Between String Theories
- Time: 11:30 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Ethan Torres, IHES, Harvard
- Abstract: Several bottom-up arguments suggest that there exist finite energy-density domain walls separating any two quantum gravity vacua. Generically, such domain walls must be non-supersymmetric and have no known formulation in string perturbation theory. In this talk, I will detail nonperturbative matrix string theory constructions of domain walls separating various 10d and 9d string theory vacua. I will discuss how these constructions can be used to compute the energy densities of such walls, and how one can understand Callan-Rubakov-like subtleties of having a domain wall separating a chiral vacuum from a non-chiral vacuum. If time permits, I will also discuss the prospects for exploring the non-BPS brane spectrum of string/M-theory more generally.
- Host: Jakob Moritz
Tuesday, November 3rd, 2026
- Condensed Matter Theory Group Seminar
- Parafermions Ex Machina
- Time: 10:00 am - 11:00 am
- Place: 3290 Chamberlin
- Speaker: Steffen Bollmann, MPI FKF Stuttgart
- Abstract: Motivated by recent observations of fractional Chern insulators (FCIs) in the vicinity of superconducting (SC) phases (e.g. $\text{MoTe}_2$), we study fractional quantum (anomalous) Hall-superconductor heterostructures in the presence of U(1) order-parameter fluctuations and particularly focus on the case of $\nu=2/3$ quantum Hall states leading to $Z_3$ parafermions. While the emergence of $Z_3$ parafermions has already been demonstrated in the spin-unpolarized Halperin State, we demonstrate how disorder can also stabilize $ Z_3$ parafermions in the spin-polarized $nu=2/3$ state, which is expected to be present in $\text{MoTe}_2$.
Due to a broad phase transition between the FCI and the superconducting state, we further study the effect of phase fluctuations on the $Z_3$ parafermions, using field-theoretical methods as well as the density-matrix renormalization group. We find a rich phase diagram composed of Mott insulating phases and two distinct Luttinger liquids, whose fundamental excitations carry charges 2e and 2e/3, respectively. In agreement with analytical considerations using conformal field theory, we numerically find transitions of Berezinskii-Kosterlitz-Thouless (BKT) type as well as a continuous $Z_3\times\text{U(1)}$ second-order phase transition characterized by central charge c = 9/5. - Host: Elio Koenig-Tarasevich
Wednesday, November 4th, 2026
- Theory Seminar (High Energy/Cosmology)
- M-theory, Casimir energy and de Sitter
- Time: 11:30 am - 1:00 pm
- Place: Chamberlin 5280
- Speaker: Rafael Alvarez-Garcia, Northeastern University, Harvard University
- Abstract: Finding de Sitter solutions is a central question in string theory. Among the various approaches, one is to use the Casimir energy from the extra dimensions to support de Sitter critical points. I will discuss upcoming work in which we analyze this for unwarped M-theory compactification on Riemann surfaces, hyperbolic manifolds and Riemann-flat manifolds, and find that such critical points cannot exist under effective field theory control.
- Host: Gary Shiu
- Department Meeting
- Time: 12:15 pm - 1:30 pm
- Place: B343 Sterling
- Speaker: Kevin Black, UW - Madiosn
- Host: Kevin Black
Thursday, November 5th, 2026
- Graduate Program Event
- Prospective Grad Info Session (PhD)
- Time: 9:00 am - 10:00 am
- Place: Sign up for this session here:
- Speaker: Sharon Kahn, Graduate Program Manager
- Abstract: Prospective PhD-Physics applicants are invited to join faculty, staff and current students for this session to learn about admissions, program requirements and life in Madison. We’ll have plenty of time for Q&A.
Sign up for this session here: - Host: Sharon Kahn
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- High-energy radiation from AGN and their connection to particle acceleration
- Time: 2:30 pm - 3:30 pm
- Place: Chamberlin Hall, Room 5280
- Speaker: Federico Testagrossa, DESY Zeuthen
- Abstract: The emergence of the Seyfert galaxy NGC 1068 as the most significant source of high-energy astrophysical neutrinos observed by IceCube marked a turning point in our understanding of the neutrino sky. This neutrino signal implies the presence of hadronic acceleration to up to 100 TeV-PeV energies. Furthermore, as neutrino production is expected to be accompanied by electromagnetic radiation of similar energies, the lack of observation of TeV gamma-rays strongly hints at the existence of a radiatively compact emission region of neutrinos, where the accompanying photons are absorbed and reprocessed at lower energies starting an electromagnetic cascade. For active galactic nuclei (AGN), the hot X-ray corona in the vicinity of the central supermassive black hole is a natural candidate for this opaque, highly energetic environment. In this talk, I will review the current understanding of neutrino emission from AGN coronae, focusing on two scenarios of non-thermal particle acceleration that successfully explained the neutrino signal of NGC 1068: acceleration in magnetic reconnection and turbulence. I will show how the multimessenger signals observed from sources like NGC 1068, within the framework of turbulent acceleration, favor a compact, strongly magnetized, and highly turbulent coronal environment. Furthermore, I will demonstrate how high radiative compactness and intense magnetic fields constrain the spectral shape of the reprocessed electromagnetic radiation, forcing the internal cascade into a universal spectral shape. Finally, I will discuss how applying these coronal models to jetted sources, such as the blazar TXS 0506+056, fails to explain their observed neutrino flux, highlighting how the production of neutrinos could happen simultaneously in different regions of the AGN, but suggesting that in blazars the most luminous emission region is located in the jet.
- Host: Ke Fang
- Astronomy Colloquium
- Migration, Tides, and the Diversity of Extrasolar Worlds
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Sarah Millholland, Massachusetts Institute of Technology
- Abstract: Many exoplanetary systems contain planets orbiting close to their host stars, with orbital periods of only days to weeks. These planets experience strong tidal forces that can reshape both their orbits and their interiors. Energy dissipation by time-dependent tidal deformations can drive orbital migration and heat planetary interiors, producing potentially observable signatures. In this talk, I will explore several outstanding puzzles in the demographics of short-period exoplanets and show how tidal evolution offers compelling explanations. I will also highlight how new observations with JWST can help test these tidal theories.
- Host: Juliette Becker
Friday, November 6th, 2026
- Physics Department Colloquium
- Searching for new particles in dense astrophysical media
- Time: 3:30 pm - 4:30 pm
- Place: Chamberlin 2241 -
- Speaker: Katelin Schutz, McGill University
- Abstract: I will discuss how we can treat various astrophysical systems, like stars and compact objects, as particle physics experiments that exist “for free” in Nature. Their relatively high densities, large volumes, and long timescales allow for even very rare microscopic processes to have large cumulative effects. In some cases, their observed properties can encode particle physics constraints that are many orders of magnitude stronger than what can be achieved in a collider experiment. Moreover, unlike the pristine conditions in a laboratory experiment, particles in astrophysical settings must propagate through dense, thermal, magnetized environments. In-medium decays and resonances can vastly enhance the production of new particles in ways that have no vacuum analog. While capturing all of these effects poses a theoretical challenge, it opens new opportunities to use existing observations to explore even more particle physics parameter space.
- Host: Dan Hooper