Perimeter Institute for Theoretical Physics

Carolina Paiva develops exact matrix product states for strongly interacting electrons in lattice bands. Conformal-field-theory correlation functions already provide exact representations of fractional quantum Hall trial wavefunctions, including Laughlin states. Extending the construction to fractional Chern insulators is obstructed by the lattice length scale. The talk shows how ideal Chern bands overcome that obstruction and derives an exact representation of Laughlin model states in a hybrid Wannier basis on a torus.

Seth Koren shows how global symmetry structure and field-space topology affect particle-physics predictions beyond the usual analysis of small field fluctuations. Different possible global forms of the Standard Model gauge group imply different model-independent predictions for fractionally charged particles. Collider searches for these particles could identify the gauge-group structure and exclude unification models. The talk then examines axion theories, using the DFSZ model to show how the global properties of scalar fields and gauge symmetries modify axion strings and can resolve the cosmological domain-wall problem.

Anna Tsai studies how precise pulsar distances can improve localization of individual gravitational-wave sources with pulsar timing arrays. A coherent map-making method uses distance information to approach the diffraction limit, potentially reaching angular precision of about two arcminutes and enabling electromagnetic counterpart searches. At a signal-to-noise ratio of ten, approximately nine pulsars can reach this limit. The resolution improves sharply as more well-timed pulsars have accurately known distances. Since the distance of PSR J0437−4715 is already measured to subparsec precision, the talk motivates coherent analyses that fully incorporate pulsar-distance information.

Sharan Banagiri uses gravitational-wave observations to investigate how stellar-mass binary black holes form. The first part of the fourth LIGO–Virgo–KAGRA observing run more than doubled the number of detections, revealing new population features and clarifying earlier ones. The talk surveys notable and puzzling subpopulations, relates them to formation channels, and connects the evidence with transient phenomena and compact-object astrophysics. As the sample grows, these identifiable subpopulations can support a broader physical account of binary black-hole formation.

Lisa Dang explores how observations reveal the three-dimensional atmospheres and climates of close-in exoplanets. Kepler and TESS have established a diverse population that tests theories of planetary formation and evolution. Tidally locked short-period planets offer strong atmospheric signals but their large day–night contrasts make one-dimensional interpretations inadequate. Measurements from JWST and precise ground-based observatories can expose these spatial differences and determine whether an atmosphere is present. The talk reviews discoveries about intensely irradiated planets and explains how the same observational techniques now investigate temperate rocky worlds and their potential habitability.

Benjamin Safdi studies the axion mass constraints obtained when grand unification and string theory are considered together with the QCD axion. Unitarity reasoning and explicit string compactifications, including examples from the Kreuzer–Skarke type-IIB ensemble, favor masses between 10^-11 and 10^-8 electronvolts. The talk explains how these theoretical frameworks combine to restrict a candidate extension of the Standard Model.

Pratika Dayal examines galaxy and black-hole formation during the first billion years, when the first galaxies ended the cosmic dark ages and began reionizing intergalactic hydrogen. JWST has revealed unexpectedly abundant, massive black holes, reaching about one hundred million solar masses within the first six hundred million years, challenging formation models. These observations can constrain the progress and spatial structure of reionization in preparation for 21-centimeter measurements. Early galaxies also test alternatives to cold dark matter. The talk considers the gravitational-wave event rates that early black holes could produce for the future LISA mission.

Luca Delacretaz investigates a nonperturbative description of Fermi surfaces, whose many low-energy excitations, collective modes, entanglement and possible non-Fermi-liquid behavior are difficult to handle with conventional field theory. Bosonization describes their dynamics using a collective field in phase space, but quantizing that field has been a longstanding obstacle beyond one dimension. The talk presents an exact description through a particular large-N limit of a level-one U(N) Wess–Zumino–Witten model, with a hierarchy of irrelevant corrections. Matrix degrees of freedom capture noncommutative phase space, and solvable strong-coupling dynamics removes the apparent excess of collective-field modes without dividing the Fermi surface into patches.

Samuel Garratt presents rigorous upper limits on entanglement entropy for locally interacting quantum many-body states at fixed energy. Ground states usually exhibit an area law, unlike generic states whose entanglement scales with volume, and gapless systems can introduce corrections. The framework constrains ground-state entanglement for gapped and gapless systems in arbitrary spatial dimension, follows the transition toward volume-law behavior as energy increases, and bounds the computational resources needed to calculate response functions at zero temperature. These results connect spectral information with the cost of tensor-network calculations.