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.
Vincent Menet (Paris, LPTHE)
13 December 2023, 15.15
Xin Wang (KIAS)
Tue 12 December 2023, 13.45
Horatiu Nastase (Sao Paolo, IFT)
29 November 2023, 13.45
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
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
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
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
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
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
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
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.
Souvik Banerjee (Würzburg U.)
Tue 13 June 2023, 13.45
Title: A universal approach to complexity
Abstract: In this talk, I shall present a general framework in which both the state and the operator complexities can be put on the same footing. This will follow from a generalized definition of complexity based on the violation of the Eigenstate Thermalization Hypothesis. In our formalism, the state complexity is defined in terms of the density matrix of the associated state which, for the operator complexity, lives on a doubled Hilbert space obtained through the channel-state map. I shall discuss how this framework also encompasses nicely, the holographic notions of complexity and explains the universal late-time growth of complexity, followed by saturation. I shall conclude with some open questions.
Paul-Konstantin Oehlmann (Northeastern U.)
Fri 09 June 2023, 13.45
Title: The geometry of twisted compactifications in M-theory
Abstract: Geometric Engineering is an important tool to engineer interesting and non-Lagrangian theories in various dimensions. If a theory admits a discrete 0-form symmetry, there is the possibility to twist by it when performing a circle reduction. Since F-theory is related to M-theory by circle reductions, this begs the question which geometries capture such twisted compactifications, what their algebraic description may be and how their moduli spaces look like. In this talk I will show that so called genus-one fibrations capture the respective twisted reductions in M-theory. I will explore the moduli space by relating twisted to untwisted compactifications via Higgs transitions of KK-charged multiplets in five dimensions. I close by outlining various applications. This talk is based on upcoming work with L. Anderson and J. Gray.
Piotr Tourkine (Annecy, LAPTh)
Thu 08 June 2023, 13.45
Title: Scattering amplitudes from dispersive iterations of unitarity
Abstract: In the late 60s, D. Atkinson proved in a series of papers the existence of functions satisfying rigorously the constraints of the S-matrix bootstrap for the 2-to-2 S-matrix of scalar, gapped theories, following an approach suggested by Mandelstam. Beyond the mathematical results themselves, the proof, based on establishing the existence of a fixed point of a certain map, also suggests a procedure to be implemented numerically and which would produce fully consistent S-matrix functions via iterating dispersion relations, and using as an input a quantity related to the inelasticity of a given scattering process. In this talk, I will present the results of a recent paper in collaboration with A. Zhiboedov, about the first implementation of this scheme. I will first review some basic concepts of the S-matrix program, and state our working assumptions. I will then present our numerical non-perturbative S-matrices, and discuss some of their properties. They correspond to scalar, massive phi^4-like S-matrices in 3 and 4 dimensions, and have interesting and non-trivial high energy and near-threshold behaviour. They also allow to make contact with the running of the coupling constant. I will also compare to other approaches to the S-matrix bootstrap in the literature.
Stijn van Tongeren (Humboldt U.)
31 May 2023, 13.45
Location: Zoom https://uu-se.zoom.us/j/61066833009
Title: Gauge theory duals of deformed integrable strings
Abstract: Integrable examples of the AdS/CFT correspondence admit numerous deformations on the AdS side, preserving this integrability. These can be viewed as AdS analogues of the real-beta Lunin-Maldacena deformation of (AdS5 x) S5. I will discuss how we can similarly deform the CFT side, in the setting of noncommutative field theory, to (hopefully) give duals of these deformed strings. The resulting noncommutative gauge theories admit a planar equivalence theorem for their Feynman diagrams, and have twisted superconformal symmetry, providing the first hints of their likely planar integrability.
Francesco Galvagno (ETH)
24 May 2023, 13.45
Title: Holographic perspectives for N=2 SCFTs in the tensionless limit
Abstract: In this talk we discuss the holographic properties of some 4d planar gauge theories in the zero coupling limit, corresponding to the tensionless limit from the string dual perspective. In particular, we consider a special family of theories, arising as orbifolds of N=4 SYM, which realize a circular quiver theory preserving N=2 superconformal invariance. Following the Gaberdiel-Gopakumar derivation, we propose a free field worldsheet theory in the tensionless string limit which is dual to the orbifold gauge theory at the free theory point. In particular, after imposing some specific gauge constraints on the worldsheet degrees of freedom, the spectrally flowed worldsheet spectrum is in one-to-one correspondence with the single trace operators of the 4d theory. Finally, we discuss possible generalizations of this approach, mentioning N=2 SCQCD as the main example.
Subhajit Mazumdar (Seoul Natl. U.)
10 May 2023, 13.45
Title: Kite and Triangle diagrams through Symmetries of Feynman Integrals
Abstract: The Symmetries of Feynman Integrals (SFI) is a method for evaluating Feynman Integrals which exposes a novel continuous group associated with the diagram which depends only on its topology and acts on its parameters. Using this method we study the kite diagram (a two-loop diagram with two external legs) and the most general triangle diagram (one-loop diagram with three external legs) with arbitrary masses and space-time dimensions. Generically, this method reduces a Feynman integral into a line integral over simpler diagrams. We identify the locus/loci in parameter space where the integrals further reduce to a mere linear combination of simpler diagrams. We generalize and revisit some known results.
Eric D'Hoker (UCLA)
26 April 2023, 13.45
Title: Cascade flow from N=2 to adjoint QCD
Abstract: The renormalization group flow is considered of N=2 super Yang Mills theory in the presence of a supersymmetry soft breaking operator, with the help of the Seiberg-Witten solution. An Abelian Higgs model is proposed as the magnetic dual to this flow near a multi-monopole point on the Coulomb branch and argued to lead from the Coulomb phase to the maximal Higgs phase through a cascade of mixed phases.
Nikolay Bobev (KU Leuven)
19 April 2023, 13.45
Title: Large N Partition Functions, Holography, and Black Holes
Abstract: I will discuss the large N behavior of partition functions of the ABJM theory on compact Euclidean manifolds. I will pay particular attention to the S^3 free energy and the topologically twisted index for which I will present closed form expressions valid to all orders in the large N expansion. These results have important implications for holography and the microscopic entropy counting of AdS_4 black holes which I will discuss. I will also briefly discuss generalizations to other SCFTs arising from M2-branes.
Irene Valenzuela (CERN and IFT Madrid)
29 March 2023, 13.45
Location: Zoom https://uu-se.zoom.us/j/61066833009
Title: Where do we live in the string landscape?
Abstract: In this talk, I will discuss the possibility that our universe lies near the boundary of the field space in string theory, including the theoretical challenges and the exciting phenomenological implications. These boundaries share some universal properties imposed by quantum gravity (sometimes promoted to Swampland constraints) that resemble our universe, like weak couplings, approximate global symmetries or small (time-dependent) vacuum energy. However, it remains as an open challenge to get an accelerated cosmology. We study whether the runaway behaviour of stringy scalar potentials towards in finite distance can produce an accelerated expanding cosmology a la quintessence, finding some potential examples in F-theory flux compactifications. I will discuss the caveats of these examples and the comparison to Swampland bounds. Furthermore, a universal feature of these regions is that there is a light infinite tower of states which is correlated to the value of the vacuum energy. I will show how experimental constraints force this tower to correspond to a KK tower (of mass of order neutrino scale) of a single extra mesoscopic dimension of order 10-6 m, which we denote as the Dark Dimension.
Pedro Liendo (DESY)
22 March 2023, 15.15
Title: Bootstrapping line defects with O(2) global symmetry
Abstract: We discuss 1d conformal line defects with O(2) symmetry using the numerical bootstrap. We start with an agnostic approach and perform a systematic bootstrap study of correlation functions of two canonical defect operators: the displacement and the tilt, without making any assumptions regarding the spectrum of the theory. We then move on to study a specific model: a localized magnetic field line defect, where we use analytic input coming from an epsilon-expansion. The interplay between analytical and numerical techniques gives intriguing results which we explore. We also comment on the generalization of our analysis to fermionic CFTs.
Giulia Isabella (IPhT, Saclay and IJCLab, Orsay)
15 March 2023, 13.15
Title: Quantum and Classical Eikonal Scattering
Abstract: I will discuss the eikonal scattering of two gravitationally interacting bodies, showing that exponentiation of the scattering phase matrix is a direct consequence of the group contraction $SU(2) \rightarrow ISO(2)$, in the large angular momentum limit. The emergence of the classical limit is understood in terms of the continuous-spin representations admitted by $ISO(2)$. We will compare the competing classical and quantum corrections to the leading classical eikonal scattering in the transplanckian regime and discuss how observables are extracted from the scattering phase matrix.
Alexander Monin (EPFL, USC)
08 March 2023, 13.45
Location: Zoom https://uu-se.zoom.us/j/61066833009
Title: Going beyond perturbative for large quantum numbers
Abstract: It is generally expected that states with large quantum numbers can be described semiclassically. In the context of CFT with additional $U(1)$ symmetry semiclassical methods allow to find the spectrum of large charge primary operators in a class of models. I will explain the methodology with an example of a scalar theory at Wilson Fisher fixed point in $d=3-\epsilon$ dimensions and show how CFT data (scaling dimensions and fusion coefficients) can be obtained systematically as the inverse charge power series. I will also present a construction allowing to identify all spinning primary operators with number of derivatives bounded by the charge in a free 3d scalar theory.
Souvik Banerjee (Würzburg U.) -- POSTPONED
01 March 2023, 13.45
Shruti Paranjape (UC Davis, QMAP)
25 January 2023, 15.15
Title: Non-Planar Geometries from Tree-Level Supersymmetric Yang-Mills
Abstract: The special structure of interactions in maximally supersymmetric Yang-Mills (SYM) allows us to construct certain scattering amplitudes on-shell. Most known geometric constructions work for N=4 SYM in the planar limit. In this talk, we make a first step towards non-planar SYM. To do this, we express tree-level amplitudes as a sum of “non-planar” contributions. These non-planar puzzle pieces appear on unitarity cuts of non-planar loop integrands. We give a nice geometric interpretation of these terms and discuss the extension of these non-planar geometries to more general cases, including a possible extension to theories of gravity.