Wednesday Seminars

Some of the seminars take place remotely on Zoom. If you would like to attend via Zoom but have not subscribed to the mailing list yet you can contact the organizers in order to obtain the passcode.

Organizers: Jacopo Sisti

Spring 2024

Claudia De Rham (Imperial Coll.)

22 May 2024, 13.15

Location: TBA

Title: TBA

Abstract: TBA

Emil Bjerrum-Bohr (NBI)

15 May 2024, 13.45

Location: TBA

Title: TBA

Abstract: TBA

Bengt Ew Nilsson (Chalmers)

24 April 2024, 13.45

Location: Å80121

Title: Squashed seven-spheres and the swampland

Abstract: We discuss recent results concerning the S7compactification of D = 11 supergravity. Using new methods based on the group G2 and octonions, the complete spectra of the two squashed seven-sphere compactifications with opposite orientations have now been determined. One of these is known to give rise to an N = 1 supersymmetric theory on AdS4 while the other (skew-whiffed) one has no supersymmetry. In both cases we find some new unsuspected features of the spectrum (singletons, degeneracies, etc) which may have interesting implications for the theory. One such concerns the issue of stability in the non-supersymmetric case. We discuss these aspects briefly in the contexts of AdS/CFT and the swampland program.

Silvia Nagy (Durham)

Tue 23 April 2024, 13.45

Location: Å101132

Title: Asymptotic symmetries for subleading soft theorems at all orders

Abstract: It is by now well understood how leading soft theorems follow as Ward identities of asymptotic symmetries defined at null infinity. For subleading infrared effects the connection is more subtle, but it turns out that this can be formalised, to all orders, by adapting the Stuckelberg procedure to construct an extended radiative phase space at null infinity. I will exemplify this with Yang-Mills theory, showing the construction of the extended phase space, as well as the charges corresponding to the subleading soft theorems at all orders.

Andres Luna (NBI, Copenhagen)

10 April 2024, 13.45

Location: Å80121

Title: All things Compton

Abstract: Recently, there has been great progress in the application of modern techniques in quantum field theory, namely the computation of scattering amplitudes, to classical systems. Most notably to binaries of black holes or other compact bodies like those producing recently detected gravitational waves. A central role in this program is played by the Compton scattering amplitude, which acts as a building block containing the necessary information to describe the aforementioned classical systems. In this talk, I will review the importance of the Compton amplitude, as well as some of its fascinating connections to black holes and salient questions.

Johan Henriksson (IPhT, Saclay)

03 April 2024, 13.45

Location: Å80121

Title: Bootstrapping mesons at large N

Abstract: At large number of colours, a confining gauge theory becomes a theory of weakly interacting hadrons. Mesons form a closed subsector, and putting constraints on tree-level meson scattering is a well-defined and tractable bootstrap problem. In my talk, I will review the EFT bootstrap and show how it applies to meson scattering. Specifically, I will explain how a few simple but carefully chosen assumptions lead us to an extremal amplitude which features a Regge trajectory with mesons at all spins, and numerical data remarkably close to real-world QCD.

Guillermo Arias Tamargo (Imperial College)

20 April 2024, 13.45

Location: Å2005

Title: The M-theory geometry of brane webs

Abstract: There are various ways of constructing 5d SCFTs in String Theory; most famously, one can look at geometric engineering in M-theory or webs of 5-branes in type IIB. It is well understood how to translate from one setup to the other in the case where the Calabi-Yau geometry is toric. However, in the type IIB picture, brane manipulations such as Hanany-Witten transitions can lead us beyond the pure toric context: the combinatorial data enconding the system has been dubbed a Generalized Toric Polygon (GTP). In this talk, I will discuss recent progress understanding the geometry of GTPs. A key role is played by the mirror Calabi-Yau, where Hanany-Witten transitions take a very simple form. This allows us to make contact with a mathematical notion of "polytope mutation", and import part of the results in that literature to our physical setup; as an example, we find "mutation invariants" that can prove useful in the classification of 5d SCFTs. Time permitting, I'll also discuss some consequences for the BPS quivers of the 5d theories engineered by GTPs.

Sven Krippendorf (Oxford U.)

06 March 2024, 13.45

Location: Zoom

Title: A new look at type IIB flux vacua via numerical methods

Abstract: String theory provides a framework to study phenomenological models of dark energy with many fields - models which have not been explored with respect to their mathematical and phenomenological structures. This has largely been due to the lack of working methods to study such solutions. In this talk, I give an overview on recent progress which allows us to study these solutions in an efficient way - heavily utilising automatic differentiation, just in time compilation and vectorisation. I illustrate this numerical framework in the context of flux vacua of Calabi-Yau compactifications of Type IIB string theory. Here we are able to obtain ensembles of solutions for several geometries which enable us to look at the statistics of phenomenological properties (e.g. |W0|) of such solutions. This allows us to identify universal structures and differences across geometries. I also present results where this framework allows us to identify for the first time long conjectured solutions with supersymmetry breaking.

Julian Sonner (Geneva U.)

28 February 2024, 13.45

Location: Å80127

Title: A tensor model for chaotic CFT

Abstract: I will describe a novel class of statistical ensembles we developed for the description of chaotic conformal field theories. These are generalisations of the usual random-matrix type theories used in the description of quantum chaotic many-body systems, and implement the kinematical as well as dynamical constraints of the CFT bootstrap. These novel statistical models take the form of distributions over random matrices and tensors. I will take some time to characterise the individual elements in terms of so-called “approximate CFTs”. Finally, I will discuss the concrete realisation of these ideas for 2D, large-c CFT and point out that the resulting tensor models (subject to reasonable constraints on the spectrum) take the form of an integral over random discrete triangularisation of 3D Euclidean manifolds, governed by the 6j symbols of Virasoro, strongly suggesting a connection to three dimensional quantum gravity.

Anton Nedelin (King's College)

21 February 2024, 13.45

Location: Å80127

Title: Relativistic elliptic integrable models and their spectra from superconformal indices

Abstract: In this talk I will present a method of derivation of both previously known and novel integrable finite difference operators and their spectra using superconformal indices of certain N=1 supersymmetric gauge theories. I will start with a very brief review of the 4d compactifications of various 6d SCFTs leading to the wide class of 4d gauge theories. Then I will show how to derive various elliptic integrable systems using superconformal indices of these 4d theories as well as some intuition coming from the geometry of 6d compactifications. Finally I will briefly discuss novel method of obtaining eigenfunctions of these integrable operators using our field theory constructions.

Larus Thorlacius (Iceland U.)

07 February 2024, 13.45

Location: Å4101

Title: Late time saturation of quantum complexity

Abstract: We study the late time behavior of holographic quantum complexity for static spherically symmetric black holes in general dimensions using a path integral formulation of the complexity-as-volume (CV) proposal. The holographic complexity exhibits an extended period of linear growth, as predicted by classical gravity, but saturates to a constant value on a time scale that is exponential in the black hole entropy. We also describe a discrete toy model for quantum complexity where the Nielsen complexity geometry is replaced by a high-dimensional hypercube.

Victor Mishnyakov (Nordita)

31 January 2024, 13.45

Location: Å4001

Title: Hidden symmetry of exactly solvable matrix models

Abstract: The prominent role of matrix models in physics and mathematics is well known. It is especially interesting that some of those models are exactly solvable, meaning the one can find explicit formulas for correlation functions. This phenomenon has also been called superintegrability of matrix models. I will present some recent attempt to study it systematically and search for its algebraic origins.

Hynek Paul (Leuven U.)

10 January 2024, 15.15

Location: Å80121

Title: Bootstrapping holographic correlators – an overview

Abstract: I aim to give an accessible overview of the recent progress in constructing correlation functions of half-BPS operators in the supergravity limit. Focussing mostly on scattering of supergravitons and supergluons in AdS5 x S5 and AdS5 x S3, respectively, I will illustrate the analytic programme at tree-level and one-loop order, and including stringy corrections. Partially based on [2309.15506] with Michele Santagata.

Fall 2023

Vincent Menet (Paris, LPTHE)

13 December 2023, 15.15

Location: Å80101

Title: New non-supersymmetric flux vacua from generalised calibrations

Abstract: We construct a new class of non-supersymmetric ten-dimensional type II flux vacua, by studying first order differential equations which are deformations of the N=1 supersymmetry conditions. We do so within the context of Generalised Complex Geometry, where there is a natural interpretation of the N = 1 supersymmetry conditions in terms of calibration conditions for probe D-branes, called D-string, domain-wall or space-filling branes, depending on them wrapping 2, 3 or 4 non-compact dimensions. We focus on a subclass of non-supersymmetric vacua violating the D-string calibration condition, where the deformation of the calibration condition is dictated by the foliated geometry of the internal space. We present the explicit construction of an example SU(3) background.

Xin Wang (KIAS)

Tue 12 December 2023, 13.45

Location: Å101158

Title: 5D Wilson Loops and Topological Strings

Abstract: Geometric engineering provides a rich class of 5D supersymmetric gauge theories with eight supercharges, arising from M-theory compactification on non-compact Calabi-Yau threefolds. The counting of BPS states in the low-energy gauge theory is determined by the degeneracies of M2-branes wrapping holomorphic two-cycles of the Calabi-Yau threefold X, which can also be calculated from the (refined) topological strings on the same manifold X. In this talk, I will explore the BPS spectrum of the 5D gauge theory with the insertion of a half-BPS Wilson loop operator, which is a charged object under the one-form symmetry. Based on M-theory realization, we derive the BPS expansion of the expectation value of the Wilson loop operator in terms of BPS sectors. It turns out that the BPS sectors can be realized and computed from topological string theories. In the unrefined limit, the BPS sectors serve as generating functions for Gromov-Witten invariants on compact (semi)-Fano threefolds constructed from X. We further conjecture the refined holomorphic anomaly equations for the VEVs of the Wilson loop operators. These equations can be used to completely solve the refined BPS invariants of Wilson loops for local \mathbb{P}^2 and local \mathbb{P}^1\times \mathbb{P}^1 completely.

Horatiu Nastase (Sao Paolo, IFT)

29 November 2023, 13.45

Location: Å2005

Title: Learning from Penrose limits of less understood gravity dual pairs

Abstract: The Penrose limit simplifies both sides of the AdS/CFT correspondence, the gravity background and the field theory (to a subset of operators), so it can be used as a tool to understand cases of holographic dual pairs that are less understood. After reviewing the method, I will apply it to cases in 4d: T-duals of AdS_5xS_5, 3d: GJV model (conformal), the MNa model and its T-dual (nonconformal), and 2d: I-branes and fibered D5-branes. I will show that we learn some things, but some are still not understood.

Paolo Vallarino (Turin U.)

15 November 2023, 13.45

Location: Å101195

Title: Strong-coupling results in N=2 superconformal gauge theories

Abstract: In this talk I will discuss recent developments in the study of different kinds of correlators in four-dimensional N = 2 superconformal gauge theories. Using supersymmetric localization, it is possible to map the computation of these correlation functions, i.e. 3-point functions of chiral primary operators and correlators of n coincident twisted Wilson loops, to an interacting matrix model and obtain expressions that are valid for any value of the ’t Hooft coupling in the planar limit of the theory. In particular, I will focus on the strong-coupling regime, where these expressions allow us to compute the leading and, sometimes, subleading orders of the correlators in an analytic way.

Elli Heyes (U. of London, LIMS)

25 October 2023, 13.45

Location: Å80121

Title: Generating Calabi-Yau Manifolds with Genetic Algorithms

Abstract: Calabi-Yau manifolds can be obtained as hypersurfaces in toric varieties built from reflexive polytopes. We generate reflexive polytopes in various dimensions using a genetic algorithm.  As a proof of principle, we demonstrate that our algorithm reproduces the full set of reflexive polytopes in two and three dimensions, and in four dimensions with a small number of points. Motivated by this result, we construct five-dimensional reflexive polytopes with the lowest number of points. We establish that many of these are not in existing datasets and therefore give rise to new Calabi-Yau four-folds.

Istvan Szecsenyi (Nordita)

18 October 2023, 13.45

Location: Å80121

Title: Regge spectroscopy of higher twist states in N=4 supersymmetric Yang-Mills theory

Abstract: We study a family of higher-twist Regge trajectories in N=4 supersymmetric Yang-Mills theory using the Quantum Spectral Curve. We explore the many-sheeted Riemann surface and show the interplay between the higher-twist trajectories and the several degenerate non-local operators, called (near-)horizontal trajectories, that have a strong connection to light ray operators, objects omnipresent in 4-dimensional Minkowskian CFTs. We resolve the encountered degeneracy analytically by computing the first non-trivial order of the Regge intercept at weak coupling, which exhibits new behaviour: it depends linearly on the coupling. This is consistent with our numerics, which interpolate all the way to strong coupling.

Alessandro Tanzini (SISSA, INFN)

04 October 2023, 13.45

Location: Å80127

Title: Surface defects, Toda equations and BPS spectra

Abstract: We show that the partition functions of 4d supersymmetric gauge theories with 8 supercharges in presence of surface defects obey a non-autonomous version of Toda system and we comment on its M-theory origin. The solution to the corresponding equations provides new recursion relations allowing for instanton counting for all simple groups from A to E. The uplift to 5d is a discrete flow generated by automorphisms of the associated BPS quiver. We show that for a class of theories, the 4d reduction of these discrete flows displays an intriguing new relation with Argyres-Douglas SCFTs.

Giulio Bonelli (SISSA)

Tue 03 October 2023, 13.45

Location: Å80127

Title: Black Hole perturbation theory from 2D CFTs & N=2 D=4 susy gauge theories

Abstract: The study of Black-Hole perturbation theory is a classical problem in General Relativity and crucial to study gravitational waves. Due to the high order of symmetry of the BH gravitational field and the consequent separation of variables at the linear order, the problem reduces to the study of linear ordinary second order differential equations. The resulting ODEs are of Fuchsian type and therefore, as already observed long ago by A.M.Polyakov, can be solved exactly in terms of classical - regular or irregular - Virasoro conformal blocks. By making use of the specific explicit expressions of the latter implied by the AGT dual perspective on the conformal field theory, it is possible to explicitly solve the connection problem of the resulting (confluent)Heun equation and give novel exact and explicit formulas for the grey body factor, quasi-normal modes and Love numbers of diverse black holes. This will be explicitly applied to 4D Kerr and Schwarzschild-(A)de Sitter BHs.

Davide Passaro (Amsterdam U.)

27 September 2023, 13.45

Location: Å80121

Title: Reversing the orientation: new frameworks for the computation of Z-hat invariants for positive Seifert manifolds

Abstract: Z-hat invariants are topological invariants for three manifolds that have deep physical meaning and are intimately related to Cern-Simons theory. Current computational methods only allow for the computation of Z-hat invariants only on a subset of Seifert manifolds which satisfy a negativity property. On such manifolds the Z-hat invariant are Quantum Modular Forms. CP symmetry on Chern-Simons theory suggests a relation between Z-hat invariant on pairs of negative and positive Seifert manifolds related by orientation reversal. A direct application of the Chern-Simons relation on known Z-hat however leads to diverging series. By leveraging the quantum modularity of the Z-hat invariant however it is possible to understand the Chern-Simons relation, and additionaly to predict the specific quantum modular properties of the proposed Z-hat invariant on positive Seifert manifolds. This prediction is known as the False-Mock conjecture. We find that, in specific cases where we can either regularize the diverging series or we can re-express the Z-hat invariant using inverted Habiro series that the relation can be applied the False-Mock conjecture is satisfied.

Franziska Porkert (Bonn U.)

30 August 2023, 13.45

Location: Å80109

Title: Massless Feynman Integrals in 2D & Single-valued Periods

Abstract: In this talk I will show how all massless Feynman integrals in two dimensions with non-integer propagator weights are related to specific single-valued objects. In the framework of intersection theory, those integrals can be evaluated as single-valued periods. At the same time, a sub-class of these integrals, the so-called fishnet integrals, can be considered in the context of Calabi-Yau geometries where they are computed by the Kähler potential or the quantum volume.

Last modified: 2024-04-22