In-person, Wednesdays at 1:00pm (student session), 1:20pm (main seminar), unless otherwise stated.
Room location is 54/5025 (5B), unless otherwise stated.
 

Semester 1  

24/09/24 - Gabi Zafrir (Haifa U., Oranim)  -  *Note unusual day*  -  1:00 / 1:20,   54 / 7035 (7B) 

02/10/24 - Will Biggs (Cambridge)

09/10/24 - Tarek Anous (QMUL) - *Note unusual time & place* - 12:00-13:00 (main seminar), 13:00-13:20 (student session) - 54/8031 (8C)

16/10/24 - Ida Zadeh (Southampton)

23/10/24 - no seminar - STAG public lecture

30/10/24 - Gabriel Wong (Oxford)

06/11/24 - Olga Papadoulaki (Ecole Polytechnique, CPHT)

13/11/24 - Saikat Mondal (IIT Kanpur)

20/11/24 - Bob Knighton (Cambridge)

27/11/24 - no seminar - STAG colloquium

04/12/24 -  Akshay Yelleshpur Srikant (Oxford)

11/12/24 - 

[Winter break: 16 Dec 2024 - 10 Jan 2025]

[Exam period: 13-24 Jan 2025]

Semester 2 

29/01/25 - 

05/02/25 - 

12/02/25 - 

19/02/25 - 

26/02/25 - 

05/03/25 - 

12/03/25 - 

19/03/25 -

26/03/25 -

[Spring break: 31 March 2025 through 25 April 2025]

30/04/25 - 

07/05/25 - 

14/05/25 -

[Exam period 19 May 2025 - 6 June 2025]

Titles and Abstracts (reverse chronological order):

Olga Papadoulaki (CPHT): An inflationary cosmology from Anti-de-Sitter wormholes

There are various proposals as to what initial state can give rise to an inflationary cosmology. The two most popular ones are the no boundary (Hartle-Hawking) and the tunneling (Vilenkin) proposals. Both of them explain only part of the observations and lead to some paradoxes. In this talk, I will review these proposals and I will propose a novel initial state (wavefunction) of the universe which in the far past has asymptotically AdS boundary conditions. In the semiclassical limit it is a Euclidean wormhole solution that can give rise to an expanding universe upon analytic continuation to Lorentzian signature. This proposal evades some of the issues that plagued the no boundary and the tunneling proposals. Moreover, the asymptotic AdS conditions in the Euclidean past could in principle allow for the description of inflationary cosmologies and their perturbations within the context of holography, leading to microscopic models. 

 Gabriel Wong (Oxford): 3d gravity as a random ensemble

One of the major insights gained from holographic duality is the relation between the physics of black holes and quantum chaotic systems. This relation is made precise in the duality between two dimensional JT gravity and random matrix theory. In this work, we generalize this to a duality between AdS3 gravity and a random ensemble of approximate CFT's. The latter is described by a combined tensor and matrix model, describing the OPE coefficients and spectrum of a theory that approximately satisfies the bootstrap constraints. We will explain how the Feynman diagrams of the random ensemble produce a sum over 3 manifolds that agrees with the partition function of 3d gravity. Our model makes explicit the intriguing relation between the sum over topologies and the implementation of the bootstrap equations.  Time permitting, we will discuss some first steps in generalizing this story to de Sitter space.

Ida Zadeh (Southampton): Heterotic islands

In this talk I will discuss asymmetric orbifolds and will focus on their application to toroidal compactifications of heterotic string theory. I will consider theories in 6 and 4 dimensions with 16 supercharges and reduced rank. I will present a novel formalism, based on the Leech lattice, to construct ‘islands’ without vector multiplets.

Tarek Anous (QMUL): Integrability in de Sitter

Perturbative calculations in de Sitter are particularly thorny: They are riddled with IR ambiguities and, at late times, signal the breakdown of the standard EFT paradigm. I will start with a light review of these issues and will motivate why exactly solvable models can be a useful tool for organizing our thoughts. To motivate these claims, I will work through a particularly simple example of such an exactly solvable model: QED in two dimensions on a fixed de Sitter background.  

Will Biggs (Cambridge): Static Charged Black Hole Binaries in AdS

Very few stationary multi-black hole solutions are known to exist. In this talk we will discuss the first examples of static binary black hole solutions in anti-de Sitter space. The attractive force between the black holes is balanced by the addition of a background electric field, sourced at the conformal boundary. I'll briefly review how these solutions can be obtained numerically before addressing some of their properties, including how they satisfy a first law relationship. We'll see that there is a continuous family of bulk solutions for a given boundary profile and temperature, suggesting there is continuous non-uniqueness of the black hole solutions. We'll discuss how this non-uniqueness is particularly surprising and confusing in the light of the AdS/CFT correspondence.

Gabi Zafrir (Haifa U., Oranim):  Dimensionally Reducing Generalized Symmetries from (3+1)-Dimensions

Recently there has been a renewed interest in the subject of novel types of symmetries, now known as generalized symmetries. An interesting question is what happens to these more general symmetry structures upon compactification to lower dimensions. In this talk, we shall explore this in the context of the compactification of 4d N=1 SCFTs to 2d on spheres.