Scientific Series

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.

As originally argued by Coleman, any breakdown of factorization arising from Euclidean wormholes may be reinterpreted as the result of having averaged over a hidden ensemble of theories. By directly categorifying Coleman's argument, we show that any breakdown of Hilbert space factorization arising from spatial wormholes (Einstein-Rosen bridges) may be reinterpreted as having projected to a subspace of neutral states in an underlying holographic quantum field theory. This talk is based on 2607.01322 with Zhencheng Wang.

The population study of stellar-mass black hole (sBH) binaries with ground-based gravitational-wave detection has achieved tremendous success in recent years. Future observations of extreme mass-ratio inspirals will similarly require proper population analyses that identify the formation channels, measure the branching ratio(s), and characterize the major properties within each channel. In this work, we propose that measurements of eccentricity, inclination, and component mass provide critical information for distinguishing different formation channels and probing detailed formation mechanisms. Focusing on dry and wet extreme mass-ratio inspirals, we establish the theoretical expectations for these observables in each formation channel. We also discuss how their distributions can be used to probe the lifetime and turbulence level of active galactic nucleus disks, the accretion patterns of supermassive black holes, and the population properties of sBHs within nuclear star clusters.

Conventional entanglement witnesses and quantum state tomography can, in principle, certify any entangled state but require prior characterization of the measurement devices. Bell tests remove this requirement but certify only those entangled states that are Bell nonlocal. In this talk, I will present a self-consistent alternative to entanglement certification. This approach uses experimentally inferred operational identities to certify entanglement through of the violation of noncontextuality inequalities, it requires no prior characterization of measurement devices and can, in principle, certify any entangled state. Finally, I will briefly discuss the complexity of self-consistent entanglement certification and its implications for developing practical self-consistent certification methods beyond entanglement.

According to the standard paradigm, all structure in the universe originated as quantum fluctuations amplified by an early epoch of cosmic inflation. If any trace of these quantum origins were to survive, it would offer a unique window into quantum physics at otherwise inaccessible scales. While standard lore suggests that the state should rapidly “classicalize” on super-horizon scales, we show this need not be the case. Using the EFT of inflation, we study quantum fluctuations non-perturbatively in backgrounds beyond slow roll by constructing the Wigner function, whose negativity provides a diagnostic for non-classicality. We find that it develops a fringe structure reflecting interference between distinct branches of the wavefunction, and that these fringes grow on the super-horizon scales responsible for seeding structure. Incorporating open system effects, we find physically motivated parameter space in which this coherence generation outpaces decoherence, suggesting these features may survive environmental interactions. Finally, I discuss how the phase-space structure of the state can guide the search for cosmological observables that retain sensitivity to its quantum origin.

Poisson sigma models sit at the intersection of deformation theory, geometry, and quantum field theory; specifically, the perturbative expansion of the two-dimensional Poisson sigma model with boundary is known to recover Kontsevich’s deformation quantization formula. In this talk, I introduce a higher-dimensional holomorphic–topological generalization of Poisson sigma models and explain their connections to the deformation quantization of holomorphic–topological factorization algebras. We also give a systematic construction of extended objects, including interfaces, enriched boundaries and defects in these theories. We explain how these models relate to the construction of quantum group-like structures via Koszul duality, and explore examples related to the quantization of Lie bialgebras, W-algebras, and Yangians.