Triangle Seminars

Abstract:
The search for extensions to GR, has prompted the developments of many potential options which, to varying degrees, have been studied and confronted with observations in special regimes –typically linear ones with respect to rather 'simple' scenarios. Gravitational wave astronomy provides the opportunity to confront them in a much richer and complex regime which unearths significant roadblocks that obstruct the definition and/or study of consequences of many of such extensions. This talk will review some of these problems, illustrate consequences and discuss a potential way through for studying the potential role such extensions might have in the strongly gravitating/non-linear regime.
[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
In this talk I will discuss how to extract the most trascendental piece of the four graviton amplitude in type IIB supergravity on AdS_5 \times S_5 at any loop order, from the dual four point function in N=4 Super Yang Mills. I will describe how to construct this part of the correlator/amplitude and its significance. I will conclude with some open problems and future directions.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]

Abstract:
``We explore the construction and stability of asymptotically anti-de Sitter Euclidean wormholes in a variety of models. In simple ad hoc low-energy models, it is not hard to construct two-boundary Euclidean wormholes that dominate over disconnected solutions and which are stable (lacking negative modes) in the usual sense of Euclidean quantum gravity. Indeed, the structure of such solutions turns out to strongly resemble that of the Hawking-Page phase transition for AdS-Schwarzschild black holes, in that for boundary sources above some threshold we find both a `large' and a `small' branch of wormhole solutions with the latter being stable and dominating over the disconnected solution for large enough sources. We are also able to construct two-boundary Euclidean wormholes in a variety of string compactifications with a similar that dominate over the disconnected solutions we find and that are stable with respect to field-theoretic perturbations. However, as in classic examples investigated by Maldacena and Maoz, the wormholes in these UV-complete settings always suffer from brane-nucleation instabilities (even when sources that one might hope would stabilize such instabilities are tuned to large values). This indicates the existence of additional disconnected solutions with lower action. We discuss the significance of such results for the factorization problem of AdS/CFT.’'


Join Zoom Meeting
https://zoom.us/j/98062076339?pwd=aGJNUTBTNjBYeDhqUlZVMzdVWkhGQT09

Meeting ID: 980 6207 6339
Passcode: 913115

Abstract:
[there will be a 15 min pre-seminar for students. For zoom link, please email s.nagyATqmul.ac.uk]
Abstract: Recent progress in understanding de Sitter spacetime in supergravity and string theory has led to the development of a 4D supergravity with spontaneously broken supersymmetry allowing for de Sitter vacua, also called de Sitter supergravity. One approach makes use of constrained (nilpotent) superfields, while an alternative one couples supergravity to a locally supersymmetric generalization of the Volkov-Akulov goldstino action. These two approaches have been shown to give rise to the same 4D action.
A novel approach to de Sitter vacua in supergravity involves the generalisation of unimodular gravity to supergravity using a super-Stückelberg mechanism. We make a connection between this new approach and the previous two. We show that upon appropriate field redefinitions, the 4D actions match up to the cubic order in the fields. This points at the possible existence of a more general framework to obtain de Sitter spacetimes from high-energy theories.

Abstract:
The \(\mathfrak{psu}(2,2|4)\) integrable super spin chain underlying the AdS/CFT correspondence has integrable boundary states which describe set-ups where \(k\) D3-branes get
dissolved in a probe D5-brane. Overlaps between Bethe eigenstates and these boundary states encode the one-point functions of conformal operators and are expressed in terms of the superdeterminant of the Gaudin matrix that in turn depends on the Dynkin diagram of the symmetry algebra. The different possible Dynkin diagrams of super Lie algebras are related via fermionic dualities and we determine how overlap formulae transform under these dualities. As an application we show
how to consistently move between overlap formulae obtained for \(k=1\) from different Dynkin diagrams. –––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.