Talks

I will introduce tropical quantum field theory, a new deformation limit of an interacting QFT. Tropical QFT is considerably easier to study than undeformed QFT, both conceptually and computationally. Remarkably, certain structural information on the initial QFT survives the tropical limit and can be used to learn about the undeformed theory. The most striking example of this so far is an algorithm, based on tropical QFT, which computes the perturbative expansion of massive scalar QFTs to a given numerical precision in a runtime that scales polynomially in the loop order and the number of external legs. This is surprising as the standard perturbative approach expands an interacting QFT around a free QFT, using Feynman diagrams. The number of these diagrams grows factorially, making this traditional approach quickly infeasible. In contrast, with the tropical approach, which is not based on a sum over all Feynman diagrams, loop order 50 becomes achievable. Tropical QFT also has an interesting geometric side: its amplitudes are volumes of moduli spaces of graphs, and their recursive structure is closely analogous to Mirzakhani's recursion for the Weil-Petersson volumes of moduli spaces of curves. I will illustrate the construction of the tropical limit, its relation to these volumes, and how the polynomial-time algorithm follows from it.

BPS operators in superconformal gauge theories can be distinguished as monotone or fortuitous according to their dependence on the gauge-group rank N, with the fortuitous sector conjectured to contain quantum black hole microstates. In this talk, I will explore fortuity beyond cohomology in U(N)_{k} \times U(N)_{-k} ABJM theory at large Chern–Simons level k. After introducing fortuity and briefly reviewing earlier cohomological results, I will discuss how to construct explicit BPS operators as harmonic representatives of the corresponding classes. The central tool is the two-loop Hamiltonian, whose continuation to non-integer N allows us to follow these operators along trajectories connecting their finite N BPS points to the large N regime. I will discuss these trajectories together with selected results for their OPE coefficients. The talk is based on joint work with Connor Behan, arXiv:2609.08052.

Next-generation spectroscopic surveys will push beyond the reach of current experiments, targeting galaxies at z > 2. This high-redshift regime is attractive for several reasons, among them the opportunity to cross-correlate galaxy samples with CMB lensing near the peak of the lensing kernel. Lyman alpha emitters (LAEs) are one of the key tracers that will enable next-generation experiments to probe these redshifts, and with imaging preparation for such surveys already under way, we can begin targeting and observing LAEs now. In this talk, I will demonstrate LAE target selection using medium-band imaging from the Intermediate Band Imaging Survey (IBIS). Using spectroscopic redshifts from Dark Energy Spectroscopic Instrument (DESI) follow-up observations, I will then present measurements of their 3D clustering, jointly fitting the LAE and QSO auto- and cross-spectra to constrain the LAE bias, Fingers-of-God effect, and the impact of radiative transfer. Our results demonstrate that LAEs can be reliably selected and modeled for next-generation surveys, marking necessary progress in the modeling preparation these experiments require.

The discovery by JWST of a large population of active black holes at z > 5, together with the evidence from Pulsar Timing Arrays for a gravitational-wave background, likely produced by supermassive black hole binaries, offers new constraints on the early growth and evolution of massive black holes. Both observations challenge standard expectations. JWST points to more numerous or more rapidly growing black holes at early times than many models predict, while the estimated PTA amplitude requires a larger than expected population of very massive black holes at low redshift. At the same time, tidal disruption events open a window onto the elusive population of intermediate-mass black holes. In this talk, I will present L-GalaxiesBH, a model that follows the formation, growth and dynamics of massive black holes and their host galaxies from their earliest emergence to the local Universe. I will then show how we jointly confront it with JWST, PTA and tidal disruption event data to constrain the model's parameters and piece together the evolutionary history of massive black holes.