Scattering of arbitrarily excited strings with applications
I will present a recent extension of the Veneziano and Shapiro-Virasoro amplitudes to the case of arbitrarily excited strings (AES) in critical bosonic string theory. I will also discuss several novel applications, such as the absorption universality emerging from the absorption cross section of AES and the emission rate of AES with particular focus on the photon and graviton emission spectrum. Finally I will comment on the spin multipole expansion and the classical infinite spin limit of three-point Heavy-Light-Heavy string amplitudes where the heavy states belong to both leading and sub-leading Regge trajectories.
28 October 2025, 14:30
Disturbing news about the 2+epsilon expansion
The O(N) Non-Linear Sigma Model (NLSM) in d=2+epsilon has long been conjectured to describe the same conformal field theory as the Wilson-Fisher O(N) fixed point obtained from the (phi^2)^2 model in d=4-epsilon. In this talk, we put this conjecture into question, building on the recent observation [Jones,2024] that the NLSM CFT possesses a protected operator with dimension N-1, which is instead absent in the WF O(N) CFT. We propose several scenarios that may explain this discrepancy.
21 October 2025, 14:30
Quantum Field Theory as a set of coupled ODEs
Correlation functions of local operators in Quantum Field Theory (QFT) on hyperbolic space can be fully characterized by the “QFT data”: scaling dimensions of boundary operators, boundary Operator Product Expansion (OPE) coefficients and Boundary Operator Expansion (BOE) coefficients for each bulk operator. We derive a universal set of first order Ordinary Differential Equations (ODEs) that encode the variation of the QFT data under an infinitesimal change of a bulk relevant coupling, for simplicity in the case in which the bulk is two dimensional.
In principle, our ODEs can be used to follow a Renormalization Group (RG) flow starting from a solvable QFT into a strongly coupled phase and to the flat space limit. As such, they are a novel non-perturbative tool to formulate predictions in weakly and strongly coupled QFTs.
07 October 2025, 14:30
Covariant phase space and L_\infty algebras
We describe a new approach to Hamiltonian mechanics based on homotopy algebras, with the aim of defining conserved charges and Poisson brackets in the context of string (field) theory,
30 September 2025, 14:30
Non-supersymmetric branes and discrete topological terms
In this talk, I will discuss the presence of a discrete topological term in heterotic strings and its implications for the consistency of the worldvolume theory of the non-supersymmetric NS5-brane. In particular, I will present evidence for the existence of this term in the non-supersymmetric heterotic theory. Furthermore, I will delve into its relation with anomaly inflow cancellation on the worldvolume of the NS5-brane. These insights will allow us to assess the consistency of candidate spectra for the six-dimensional theory living on these defects.
23 September 2025, 14:30
The holography of solitons
I will discuss the relation between different states in a QFT to the existence of soliton solutions in supergravity. Based on: 2104.14572, 2210.06319
08 July 2025, 14:30
External probes of conformal field theories (CFTs) introduce novel observables and provide new insights into their structure. Well-known examples include CFTs in curved space, at finite temperature, or with a non-zero chemical potential. A key tool in this exploration is the low-energy effective action, which can be systematically constructed using symmetry principles. In this talk, we will focus on three-dimensional CFTs with a global U(1) symmetry coupled to a background magnetic field. Assuming that the magnetic field drives the CFT to a gapped phase, we will examine the associated effective action and use it to define two-point functions of the conserved current and stress-energy tensor. Leveraging dispersive arguments, we will derive constraints on the effective action coefficients and explore their implications for physically relevant observables.
17 June 2025, 14:30
A Geometric Relational framework for General Relativistic theories
After reminding why relationality is the paradigmatic physical insight of General Relativistic theories, we discuss the bundle geometry of their field space. In that context we present a framework that allows to systematically produce a diffeomorphism-invariant and manifestly relational reformulation of a theory. This approach is shown to encompass various constructions found in the literature, old and new. We finish by stressing how the framework extends naturally to general-relativistic gauge field theories, and how it leads naturally to what we call 'relational quantization'.
10 June 2025, 14:30
I will discuss on-going efforts to solve constructively crossing equations in the context of the conformal bootstrap. Emphasis will be given to numerical approaches based on large-scale, non-convex optimization methods and the potential to address such problems with Machine Learning techniques. I will present one successful application of these methods in the framework of bootstrability for half-BPS Wilson lines in 4d N=4 SYM theory.
20 May 2025, 14:30
Dualities and the Compactifiability of Moduli Space
After introducing (self-)dualities in string theory and their action on the field content & spectrum of the theory, I will present the notion of compactifiability for the moduli space of massless fields as the condition that its volume is finite or grows no faster than Euclidean space. I will argue that compactifiability generically implies the existence of non-trivial dualities by providing evidence from string theory. Moreover, I will explain how one can connect compactifiability to the condition that the spectrum of objects charged under the duality group transform in a semisimple representation. Finally, I will provide a bottom-up argument for compactifiability, and argue that it (at least in supersymmetric cases) can be explained by the finiteness of the number of massless states upon compactification to 1D. Based on arXiv:2412.03640.
06 May 2025, 14:30