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 - 59 / 1257 -

18/11/25 - 02 / 1083 - Eggon Viana (Durham)

25/11/25 - 54 / 5027 (5A) - 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):

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.