Format of the string theory seminars (Tuesdays at 1:00pm):

1) 20min student session
2) Seminar itself 1hr + questions

Schedule

Semester 1 

30/09/25 - 100 / 3023 (S/R) -Zihan Yan (Cambridge)

07/10/25 - 59 / 1257 - Georgios Papadopoulos (King's) 

14/10/25 - 06 / 1081 - Mike Blake (Bristol) 

21/10/25 - 13:30 [note unusual time] - 02 / 1083 - Duncan Haldane (Princeton University)

28/10/25 - 54 / 7033 (7C) -  Jacopo Papalini (Ghent) 

04/11/25 - 54 / 7033 (7C) -  Francesco Nitti (APC, Paris)

11/11/25 - 02 / 3043 - Mitchell Woolley (Queen Mary)

18/11/25 - 02 / 3043 - Eggon Viana (Durham)

25/11/25 - 02 / 3043 - Job Feldbrugge (Edinburgh)

02/12/25 - 54 / 5025 (5B) - Ben Craps (VUB)

09/12/25 - 54 / 7033 (7C) - Murat Koloğlu (Queen Mary)

16/12/25 - 54 / 7033 (7C) - Alessandro Podo (IHES)

[Winter break: 14 Dec 2025 - 4 Jan 2026]

[Exam period: 12-23 Jan 2026]

Semester 2 

27/01/26 - João Miguel Vilas Boas (Queen Mary)

03/02/26 - Costis Papageorgakis (Queen Mary)

10/02/26 -

17/02/26 - 

24/02/26 - 

03/03/26 - 

10/03/26 - 

17/03/26 - 

[Spring break: 22 March 2026 through 19 April 2026]

21/03/26 - 

28/04/26 - 

05/05/26 - 

12/05/26 -  

[Exam period 18 May 2026 - 6 June 2026]

Titles and Abstracts (reverse chronological order):

Job Feldbrugge (University of Edinburgh): Unravelling the cosmic web with caustics

Abstract: The cosmic web is the largest geometric structure in our universe, consisting of an intricate network of empty voids bounded by thin walls, elongated filaments, and dense clusters. Building on the work of Zel’dovich and Arnol’d, I will classify these geometric features in the three-dimensional cosmic web in terms of their formation histories, using the 7 elementary catastrophes (the fold, cusp, swallowtail, butterfly and umbilic catastrophes) of Catastrophe theory. By tracking the different caustics, we obtain the caustic skeleton of the cosmic web, identifying the propto-walls, filaments and clusters of the large-scale structure in the primordial gravitational potential. Each structure in the cosmic web is uniquely linked to a caustic and a specific patch in the Gaussian initial conditions, explaining the geometry of the cosmic web we observe today. The caustics demonstrate how the different elements of the cosmic web are related and show a strong correlation with the embedded galaxies. The nature of the different elements of the cosmic web is systematically studied with constrained Gaussian random field theory in N-body simulations.

Catastrophe theory will likely enable us to quantify the geometry and topology of the cosmic web in upcoming cosmological redshift surveys. At the same time, I will show how catastrophe theory and the developed techniques can be applied to many non-perturbative phenomena in physics and mathematics, ranging from dynamical systems and lensing to the real-time quantum evolution studied with the Feynman path integral.

Eggon Viana (Durham): Worldline amplitudes using pure spinor formalism

Abstract: Superstring theory in ten dimensions admits a field theory limit describing a superparticle propagating in a 10D super-Yang-Mills (SYM) background. The scattering amplitudes of this field theory can be derived either as limits of superstring amplitudes or directly from field-theoretic computations. In this talk, I will give the ingredients for the derivation of the 10D SYM amplitudes from the superparticle perspective, using the pure spinor formalism. Although this approach reproduces known results, it provides powerful methods for constructing more general worldline amplitudes. This general method becomes essential when dealing with theories that do not arise as limits of string theory, most notably the eleven-dimensional supergravity. I will show how the pure spinor formulation of the superparticle in an 11D supergravity background leads naturally to a worldline prescription for computing 11D supergravity amplitudes at tree level.

Mitchell Woolley (Queen Mary): The W-algebra bootstrap of 6d (2,0) theories

Abstract: We outline progress toward the superconformal bootstrap of the 6d (2,0) SCFTs. The first step was achieved in [2506.08094], where we used the conjectured cohomological reduction of 6d (2,0) SCFTs to W-algebras to extract an infinite set of protected mixed correlator CFT data. To that end, we explicitly construct the W_g algebras of 6d (2,0) theories of type g={A,D} and impose Jacobi identities on generator OPEs to fix CFT data. We uplift this data and the twisted correlators to 6d and show how our CFT data is organized in conformal Regge trajectories. As an application, we demonstrate the consistency of this information with protected higher derivative corrections in the M-theory holographic dual on AdS_7 x S^4/Z_o.

Francesco Nitti (APC, Paris): Holographic QFT Dynamics on curved spacetimes

Abstract: I will discuss how the gauge/gravity duality can be used to investigate strongly-coupled field theories when they are defined on a curved background spacetime. Focusing on models based on Einstein-Dilaton gravity, I will discuss how the background curvature affects RG-flows to IR fixed-point,  IR physics in confining theories, and properties of the spectrum. I will show how certain holographic theories display phase transitions,  as a function of the curvature, which may be first order or continuous.

Jacopo Papalini (Ghent): Sine dilaton gravity: wormholes, finite matrices and q-holography
Abstract: I will discuss a two-dimensional dilaton gravity theory with a sine potential. At the disk level, this theory admits a microscopic holographic realization as the double-scaled SYK model. Remarkably, in the open channel canonical quantization of the theory, the momentum conjugate to the length of two-sided Cauchy slices becomes periodic. As a result, the ERB length in sine dilaton gravity is discretized upon gauging this symmetry. For closed Cauchy slices, a similar discretization occurs in the physical Hilbert space, corresponding to a discrete spectrum for the length of the necks of trumpet geometries. By appropriately gluing two such trumpets together, one can then construct a wormhole geometry in sine dilaton gravity whose amplitude matches the spectral correlation functions of a one-cut matrix integral. This correspondence suggests that the theory provides a path integral formulation of q-deformed JT gravity, where the matrix size is large but finite, thus going beyond the regime of the double-scaled SYK model. Finally, I will describe how this theory of gravity can be regarded as a realization of q-deformed holography and propose a possible implementation of this framework to study the near-horizon dynamics of near-extremal de Sitter black holes.

Duncan Haldane (Princeton): Quantum geometry in the quantum Hall effect

Mike Blake (Bristol): Classically Simulable Operator Scrambling
Abstract: A fundamental aspect of quantum mechanics is the scrambling of quantum information - how information encoded in an initial state or operator gets spread out, scrambled, across many degrees of freedom under time evolution. For generic chaotic many-body quantum systems, numerically studying scrambling is exponentially hard in the number of qubits, and as such can only be done for small system size. I will describe a novel type of many-body quantum dynamics known as super-Clifford circuits, for which certain probes of operator scrambling can be efficiently simulated on a classical computer. In particular, I will show that in such circuits both operator entanglement and OTOCs can be efficiently computed for a large class of many-body operators. Furthermore, these super-Clifford circuits include examples of fast scramblers, in the sense that the operator entanglement of these many-body operators saturates as quickly as allowed by fundamental bounds.

Georgios Papadopoulos (King's College): Sigma model RG flows, singularities and cosmology
Abstract: I shall explain how the behaviour of sigma model RG flows can be investigated using the Perelman's method of proving the Poincare conjecture.  The results will include a proof for the monotonicity of the RG flow and a proof that all scale invariant sigma models with compact target space are, in fact, conformally invariant.  Other results include an analysis of the nature of the singularities in the RG flow that indicate strong coupling behaviour. Also, I shall present some potential applications to cosmology like the mergence of cosmological constant in a string theory setting and a way to prove the homogeneity and isotropy of the universe at large scales. The talk is based on 2404.19526 (with E. Witten) and 2509.13092.

Zihan Yan (Cambridge): Perspectives on thermodynamics of non-stationary horizons

Abstract: In this talk, I introduce two complementary approaches to study the thermodynamics of horizons perturbatively away from stationarity in arbitrary diffeomorphism-invariant theories of gravity with non-minimal matter couplings. (1) Light-ray focusing: on the dynamical horizon, we prove a generalised focusing theorem encoding horizon thermodynamics: under positive null energy flux, light rays converge when their expansion is measured by the Wall entropy density rather than the area element. Wall entropy extends Bekenstein–Hawking and Wald entropies and satisfies the first and second laws. With higher-spin fields, the theorem and laws persist subject to a “higher-spin focusing condition”, proposed as a consistency constraint. (2) Symmetry: near-stationary horizons possess a perturbatively broken boost symmetry whose improved Noether charge defines the Hollands–Wald–Zhang dynamical entropy, which offers another dynamical generalisation of Wald entropy. We extend this from pure gravity to general theories with arbitrary bosonic matter couplings, analyse horizon temperature variations, and treat charged black objects—strings, rings, and branes, etc.—with p-form charges in one framework, deriving the associated first and second laws. Finally, the two approaches unify: the event-horizon dynamical entropy equals the Wall entropy of the generalised apparent horizon.