In-person, Tuesdays at 1:00pm (student session), 1:20pm (main seminar), unless otherwise stated.
 

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 - TBC - Duncan Haldane (Princeton University)

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

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

11/11/25 - 54 / 7033 (7C) -

18/11/25 - 54 / 7033 (7C) -

25/11/25 - 54 / 7033 (7C) -

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

09/12/25 - 54 / 7033 (7C) -

16/12/25 - 54 / 7033 (7C) -

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

[Exam period: 12-23 Jan 2026]

Semester 2 

27/01/26 - 

03/02/26 -

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):

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.