Non-invertible symmetries, anomalies and scattering amplitudes.

We show that crossing symmetry of S-matrices is modified in certain theories with non-invertible symmetries or anomalies. Focusing on integrable flows to gapped phases in two dimensions, we find that S-matrices derived previously from the bootstrap approach are incompatible with non-invertible symmetries along the flow. We present consistent alternatives, which however violate standard crossing symmetry and obey modified rules dictated by fusion categories. Based on work with Christian Copetti and Shota Komatsu.

12th March 2024, 14:30

Orientifold reductions with fluxes and dynamical open strings

I will explain in detail how a compactification of type II string theory with orientifold planes and parallel D-branes with dynamical open strings may be effectively described by a lower-dimensional half-maximal gauged supergravity coupled to a generic number of vector multiplets. In particular, I will illustrate it explicitly in the context of orientifold reductions of type IIB down to 6d. Then I’ll sketch how this machinery can be applied to massive IIA reductions to 4d, as well. I will also discuss some preliminary results concerning 6d & 4d vacua.

5th March 2024, 14:30

Non-supersymmetric heterotic strings on tori

In the absence of experimental evidence for supersymmetry, compactifications of the non-supersymmetric heterotic strings make their reappearance in the landscape of possibly phenomenologically-relevant backgrounds. Furthermore, they have been recently used to build non-supersymmetric AdS backgrounds, which according to one of the swampland conjectures, should not be part of the landscape. In this talk we will analyse compactifications on string-size tori, focusing on the phenomenon of gauge symmetry enhancement at special points in moduli space.Concentrating on the circle, we find all the points that have non-Abelian gauge symmetries of maximal rank, and analyze their matter spectrum. We show that all gauge symmetry enhancements, and where they are realised in moduli space, can actually be obtained from an extended Dynkin diagram. We will show the one-loop cosmological constant, as well as its Hessian at points of maximal enhancement, finding a surprising result. Finally, we will discuss their use in building non supersymmetric AdS backgrounds.

27th February 2024, 14:30

Quantum Spacetime, Noncommutative Geometry and Quantum Observers

Since the dynamical variable of general relativity is spacetime itself, it is natural to think that a quantization of gravity requires a quantization of spacetime, possibly described by a noncommutative geometry. Such a quantum spacetime requires quantum symmetries, and a quantization of observers/references frames. I will introduce the necessity for a quantum spacetime, and describe some instances for which symmetries and observers are likewise quantized.

20th February 2024, 14:30

Quantized Strings and Instantons in Holography

I will present two examples where we compute worldsheet instanton contributions to holographic observables in type IIA string theory. In the first case, the string lives in a ten-dimensional background geometrically realized by spherical D4-branes and dual to maximally supersymmetric Yang-Mills on a five-dimensional sphere. In the second example the background is AdS4 x CP3, which is dual to ABJM in the type IIA limit. Our computations match non-perturbative corrections to the dual field theory free energy obtained via supersymmetric localization. If time allows, I will also discuss the extension of such analysis to semiclassical M2 brane partition functions in eleven-dimensional backgrounds, and their field theory duals.

13 February 2024, 14:00

Bootstrapping the Long-Range Ising model

We combine perturbation theory with analytic and numerical bootstrap techniques to study the critical point of the long-range Ising (LRI) model in two and three dimensions. This model can be interpreted as a conformal defect in an auxiliary, free scalar bulk CFT. We explain how this interpretation can be used in order to gain non-perturbative information on the critical behaviour of LRI. When we combine these approaches within the numerical bootstrap. We find a family of sharp kinks for two- and three-dimensional theories which compare favourably to perturbative predictions, as well as some Monte Carlo simulations for the two-dimensional LRI. (Based on 2311.02742.)

7 February 2024, 14:00

Harmonic analysis and the conformal bootstrap reloaded

I will discuss a connection between harmonic analysis on hyperbolic n-manifolds and conformal field theory in n-1 dimensions. Used in one direction, this connection leads to new spectral bounds on hyperbolic manifolds. Used in the other direction, it offers a new viewpoint on the spectral data of conformal field theories.

30 January 2024, 14:00

Low d singularities

We study black holes in two and three dimensions that have spacelike curvature singularities behind horizons. The 2D solutions are obtained by dimensionally reducing certain 3D black holes, known as quantum BTZ solutions. Furthermore, we identify the corresponding dilaton potential and show how it can arise from a higher-dimensional theory. Finally, we show that the rotating BTZ black hole develops a singular inner horizon once quantum effects are properly accounted for, thereby solidifying strong cosmic censorship for all known cases.

23 January 2024, 14:00

The Regge bootstrap for weakly coupled dual model amplitudes

Dual models describe the tree-level exchange of infinitely many higher spin resonances, as in tree-level string theory and large N gauge theories. They are the simplest non-trivial scattering amplitudes that one can hope to build explicitly. Yet, numerically bootstrapping them has proven extremely difficult, in part because of the slow convergence of their expressions as infinite sums. In this talk I will present a numerical linear programming bootstrap to construct dual model amplitudes from the data of their Regge trajectories. The bootstrap method relies on an efficient parametrization of the amplitude in terms of Mandelstam-Regge poles, and a thorough understanding of the analytical structure of this expansion in the complex plane. After introducing some basic notions on Regge theory and explaining the method, I will show some first results obtained with it: Firstly I will explain how it is possible to "rediscover" the Veneziano amplitude within this framework by constraining our ansatz for the amplitude to a restricted parameter space, and then I will use the lessons learned from this exercise to investigate a toy-model deformation with bending trajectories mimicking some features of QCD.

16 January 2024, 14:00

Perturbative three-point functions and uniform transcendentality in N=4 SYM

In this talk I will present a few conjectures on the transcendental weight of certain two-point functions of local operators in N=4 SYM, at perturbative level. I will also describe a three-loop calculation of structure constants in N=4 SYM with two spinning operators, which inspired those conjectures.

09 January 2024, 14:00