I will discuss our recent calculations of the observables involved in the scattering of two black holes or neutron stars at fourth post-Minkowskian order (three loops) using the Worldline Quantum Field Theory (WQFT) framework. These 4PM observables now include both spin-orbit and adiabatic tidal corrections — inclusion of the latter necessitates a renormalization of the underlying classical effective field theory (EFT). I will also explain how the Effective-One-Body (EOB) may be used to resum the observables, and provide input data for future-generation gravitational waveform models.

We present a new formulation of string and particle amplitudes that emerges from simple one-dimensional models. The key is a new way to parametrize the positive part of Teichmüller space. The formulation works at all orders in the perturbation series, including non-planar contributions to the amplitudes. The relationship between string and particle amplitudes is made manifest as a "tropical limit". The results are well adapted to studying the scattering of large numbers of particles or amplitudes at high loop order. The talk will in part cover results from arXiv:2309.15913, 2311.09284.

We propose a theoretical framework that explains how the mass of simple and higher-order networks emerges from their topology and geometry. We use the discrete topological Dirac operator to define an action for a massless self-interacting topological Dirac field inspired by the Nambu–Jona-Lasinio model. The mass of the network is strictly speaking the mass of this topological Dirac field defined on the network; it results from the chiral symmetry breaking of the model and satisfies a self-consistent gap equation. Interestingly, it is shown that the mass of a network depends on its spectral properties, topology, and geometry. Due to the breaking of the matter–antimatter symmetry observed for the harmonic modes of the discrete topological Dirac operator, two possible definitions of the network mass can be given. For both possible definitions, the mass of the network comes from a gap equation with the difference among the two definitions encoded in the value of the bare mass. Indeed, the bare mass can be determined either by the Betti number β0 or by the Betti number β1 of the network. We provide numerical results on the mass of different networks, including random graphs, scale-free, and real weighted collaboration networks. We also discuss the generalization of these results to higher-order networks, defining the mass of simplicial complexes. The observed dependence of the mass of the considered topological Dirac field with the topology and geometry of the network could lead to interesting physics in the scenario in which the considered Dirac field is coupled with a dynamical evolution of the underlying network structure.

In the 2nd lecture, we dig into the underlying logic of entanglement bootstrap. Illustrative examples are aimed to be simple but nontrivial. The following will be included: (1) We explain a few basic uses of strong subadditivity and quantum Markov states; we explain why axiom A0 is crucial to protect coherence. We derive the information convex set of the sphere as an application. (2) Related to the information convex set of the annulus, we explain the definition of quantum dimensions, why the vacuum has the smallest entropy, and why a certain "merged state" has the maximum entropy. (3) We classify immersed annuli on a sphere and explain why some puzzles of figure-8 annulus are not solved in naive ways. (4) In the context the reference state has a 0-form symmetry, we sketch a way to create a symmetry defect line, which (in some models) permutes anyons. This lecture is given using an ipad and is, thus, flexible. We also discuss topics from questions (feedbacks) during the 1st (and 2nd) lecture. See https://www.london-tqft.co.uk for details.

In the calculation of the perturbative amplitude of superstring theory at one loop, modular graph functions (MGFs) emerge as notable mathematical constructs. These MGFs, representing Feynman diagrams on the surface of a torus, must be integrated over the fundamental domain. My talk will introduce MGFs, elucidate their generating series, and delve into the concept of equivariance, playing a key role in classifying MGFs. Additionally, I will cover recent advancements in understanding the generating series of MGFs and the integration of MGFs over the fundamental domain.

We analyze a model of qubits which we argue has an emergent quantum gravitational description similar to the fermionic Sachdev-Ye-Kitaev (SYK) model. The model is generic in that it includes all possible q-body couplings, lacks most symmetries, and has no spatial structure, so our results can be construed as establishing a certain ubiquity of quantum holography in systems dominated by many-body interactions. We will discuss implications for Hamiltonian complexity, the factorization problem in quantum gravity, and quantum simulations of holography. Based on 2311.01516 with Mike Winer.

Topological quantum field theory can emerge in gapped many-body quantum systems at low energies. In 2+1D systems, anyons can emerge, and in 3+1D, emergent excitations, including point-particles and loops-like excitations, possibly knotted or linked. In this lecture, we introduce an ongoing effort to understand (in fact, derive) laws of the emergent theory in 2+1D, 3+1D, (and higher D) gapped systems from a few axioms about the entanglement of a many-body ground state wave function. This research program, referred to as entanglement bootstrap, is an approach independent of quantum field theory, and it uses nontrivial quantum information and topology ideas. We explain the axioms and key concepts. We sketch the proof of several main theorems, including the definition of superselection sectors (anyons in 2+1D, point and loop excitations in 3+1D), the fusion spaces, and their constraints. We explain why immersion (i.e., local embedding) is valuable for, e.g., putting systems on closed space manifolds and what we hope to learn next. (see https://www.london-tqft.co.uk for more details)

We discuss the initial boundary value problem in general relativity (with vanishing cosmological constant). We consider a non-standard set of boundary conditions, known as conformal boundary conditions, where the conformal class of the induced metric and the trace of the extrinsic curvature are fixed at the boundary. We compare these results with analogous results for the Dirichlet problem both in Lorentzian and Euclidean signature, where a notion of conformal black hole thermodynamics will be developed. Time permitting, we will discuss implications for holography and de Sitter space.

There has recently been a lot of activity in the field of generalised symmetries. In the context of supersymmetric gauge theories with interesting moduli spaces of vacua, such as 3d N=4 theories, global symmetries may enjoy a geometric interpretation: they act as isometries of the moduli space. In this talk I will informally put forward the idea that by enhancing the notion of moduli space one can in a similar fashion geometrise generalised symmetries. I will focus on simple 3d N=4 abelian example and talk about various things including what I'll call 0- and 1-form resolutions as well as automorphism 2-groups.

I will present the problem of building local AdS bulk observables from boundary CFT data. Focusing on QFTs coupled to a rigid AdS background, we study the analyticity constraints that bulk locality imposes on bulk-boundary-boundary 3-point functions ("AdS form factors"). We reformulate these constraints as a complete, non-perturbative set of sum rules. These sum rules lead to additional constraints on the boundary CFT on top of crossing, and can be implemented numerically in the bootstrap. We study the flat limit when these "AdS form factors" become form factors. (Based on 2305.07078)

The TTbar deformation is an irrelevant deformation of 2D field theories associated with nonlocal UV behaviour. Despite its apparent solvability, many aspects of the deformation remain mysterious. In this talk, I will present exact results for the TTbar deformation of 2D U(N) Yang-Mills theory. Carrying out the analysis at the level of each instanton sector, we can determine the nonperturbative contributions to the partition function and prove that the spectrum undergoes a truncation (a property only conjectured for other TTbar-deformed theories). We then derive the large-N limit by studying the relevant flow equation, uncovering a rich phase diagram where phase transitions are driven by instanton condensation.

The Bekenstein-Hawking entropy of 1/16-BPS AdS_5 black holes is captured by a superconformal index. Such indices exhibit SL(3,Z) modular properties, which are explicated in terms of ambiguities in the Heegaard splitting of an associated Hopf surface. We conjecture a "modular factorization" of superconformal indices of general N=1 gauge theories and provide evidence for this conjecture by studying the free chiral multiplet and SQED.

Long range entanglement is a conceptually useful notion in the physics of quantum phases of matter. E.g. in (2+1) dimensions, ground states display area law entanglement with a potential constant correction: the "topological entanglement entropy" (TEE) which is a smoking gun of topological order. Through the lens of the IR effective field theory, described by topological quantum field theory (TQFT), we encounter the following puzzle: how does a field theory with a finite dimensional Hilbert space support a divergent area law? The simple resolution to this puzzle will also suggest an alternative perspective on topological entanglement. Utilizing the algebraic formulation of entanglement I will define a quantity I will call "essential topological entanglement." It is (i) strictly topological, (ii) positive, (iii) finite, and (iv) displays more long-range features than traditional TEE. Working with Abelian p-form BF theory as an example, I will explain general aspects of essential topological entanglement. I will elaborate on potential further applications of essential topological entanglement, as well as describe some follow-up work regarding the entanglement carried by edge-modes in BF theory.

In this talk I will provide briefly summarize the status of numerical lattice simulations of supersymmetric gauge theories. As an example I will focus on low dimensional supersymmetric Yang-Mills theories in the context of gauge/gravity duality.

Decoherence and thermalisation of isolated many-particle quantum states are studied in many different subfields of physics, including high-energy physics. One of the most interesting case are Heavy Ion Collisions which can be holographically connected to string theory in Anti-de Sitter space and for which very detailed data exists. After a general introduction I will focus on the question whether SU(N) gauge theories behave as predicted by the Eigenstate Thermalization Hypothesis (ETH). To answer this question we have performed simulations for low-dimensional SU(2) gauge theories on digital computers (arXiv: 2308.16202) which gave encouraging results. As ETH makes predictions for energy eigenstates the most natural theoretical approach to study e.g. thermalization of QCD is the numnerical simulation of Hamiltonian lattice QCD on quantum computers which, however, is not yet possible. Investigating the validity of ETH on digital computers is an early step in this direction.

We consider black hole linear perturbation theory in a four-dimensional Schwarzschild (anti-)de Sitter background. We describe two methods that provide the quantization condition for the quasinormal mode frequencies of the perturbation field. The first consists of using the Nekrasov-Shatashvili functions, or, equivalently, the classical Virasoro conformal blocks, to obtain the connection coefficients for the differential equation encoding the spectral problem. The second method is based on a perturbative expansion of the local solutions of the differential equation, that involves multiple polylogarithmic functions. We conclude by showing how the two methods shed light on the mathematical structure of the quasinormal mode frequencies, and discussing how they can be generalized to problems in different backgrounds, emphasising their effectiveness.

Tambara-Yamagami (TY) 1-categories provide the mathematical framework to describe the algebra of extended operators of (1+1)-d theories that admit a duality defect. In this talk I will define what is the generalization of TY 1-categories for fusion 2-categories, and how to construct them from fusion 2-categories that are group-theoretical. I will also explain that group-theoretical fusion 2-categories are completely characterized by the property that the braided fusion 1-category of endomorphisms of the monoidal unit is Tannakian. Using this characterization, I will show when a fusion 2-category admits a fiber 2-functor.

String theory has far surpassed expectations in its ability to shed light on many areas of theoretical and mathematical physics. However, partly due to the immense size of the solution space, it is yet to be determined if our universe lives somewhere in the string landscape. In this talk, I will present how methods from computer science (genetic algorithms and reinforcement learning) can shed some light on these questions by exploring promising regions of the string landscape. Specifically, reinforcement learning and genetic algorithms are used to construct sums of line bundles and monad bundles on smooth Calabi-Yau threefolds, for compactifications of E8xE8 heterotic string theory.

In this talk we will attempt to reconcile two different results on two-dimensional pure Yang-Mills theory. Specifically, we will discuss how the fact that 2d pure Yang-Mills is equivalent to a disjoint union of theories, is related to the Gross-Taylor description of 2d pure Yang-Mills as the target-space field theory of a string theory. The Gross-Taylor picture can be understood by first rewriting the Yang-Mills partition function (in a large N limit) as a sum of correlation functions in Dijkgraaf-Witten theories for the symmetric group S_n, and then interpreting those Dijkgraaf-Witten correlation functions in terms of branched covers, which leads to the string theory description. We first observe that the decomposition of the pure Yang-Mills aligns perfectly with decomposition of S_n Dijkgraaf-Witten theory, and then discuss decomposition and the branched covers interpretation. We encounter two puzzles, and to solve them, propose that the Gross-Taylor string theory has a higher-form symmetry.

We will discuss how amplitudes can be used to efficiently derive classical gravitational-wave observables characterizing black hole binary encounters. This technique is very flexible and can be applied to General Relativity, but also to its extensions and, in the spirit of Effective Field Theory, can be used to describe compact objects beyond Schwarzschild black holes. We will briefly discuss some recent applications to spinning black holes and to the subleading Post-Minkowsian waveforms.