Consistent truncations and KK spectra via exceptional field theory
In this seminar I will discuss how Exceptional field theory provides us with a natural framework to study AdS vacua and their CFT duals. I will start with a review of consistent truncations and their construction in ExFT, I will then describe two recent examples. In the first we constructed a new consistent truncation of type IIB supergravity on S^3xS^3xS^1. We then found several families of AdS3 vacua preserving various amounts of supersymmetry in 3 dimensions and uplifted the solutions to 10 d. In the second example we found a domain wall solution interpolating between the squashed and round S^7 vacua of 11 d supergravity. We then used the machinery of KK spectrometry to compute the quadratic couplings of fluctuations along the flow.
21 November 2023, 15:00
Approximate CFTs and Random Tensor Models
Over the past few years, the importance of chaos in the physics of quantum black holes has become clear. This is particularly well understood in two-dimensional gravity, where the boundary system is quantum mechanics. Quantum chaos is well understood in quantum mechanics, going back several decades to the work of Wigner, in terms of random matrix universality: the statistical spectral correlations of a chaotic hamiltonian are indistinguishable from those of a random matrix drawn from the appropriate ensemble. Quantum chaos is much less understood in quantum (and conformal) field theories, which appear in top-down realizations of AdS/CFT. What is the right ensemble of theories to draw from in the case of field theories, similar to the random matrix ensembles of Wigner? In this talk, I will review progress on this front, and explain how to incorporate the many CFT constraints into a framework of ensemble of CFTs.
14 November 2023, 14:30
Recently, there has been considerable interest in quantum field theories in two dimensions deformed by the irrelevant “TTbar” operator defined by the determinant of the stress-energy tensor. TTbar-like flows have also been shown to characterise effective field theories in higher dimensions. In this talk, I will review part of this research topic and describe results on TTbar deformation of supersymmetric theories, the role of TTbar-like flows for theories of non-linear electrodynamics in D=3,4, and the definition of a new (classically) marginal Root-TTbar deformation in 2D.
07 November 2023, 14:30
Higher derivative supergravity from superspace
In this talk, I will review key ingredients used to construct off-shell higher-derivative invariants in (gauged) supergravity theories. The construction is based on an interplay between the superconformal tensor calculus, the superform approach to construct supersymmetric invariants, and novel off-shell superspace techniques. I will discuss how to obtain curvature-squared (four-derivative) invariants for (gauged) minimal supergravities in five (5D) and six (6D) dimensions, including the Gauss-Bonnet invariant, which is linked to the description of alpha'-corrections to the low-energy limit of compactified string theory. Time permitting, I will review how to obtain the two 6D N=(1,0) and single 6D N=(2,0) (six-derivative) conformal supergravity actions that describe type B anomalies of six-dimensional conformal field theories.
06 November 2023, 14:30
Decoding discrete distances
Characterizing vacua is one of the first targets when studying a physical system. In string theory, vacua near boundaries of moduli spaces have distinguished properties, which are related to their underlying geometry in a simple way. This is the essence of the swampland distance conjecture. I will extend these ideas to a notion of geometry for discrete sets of isolated vacua, which ought to arise when moduli are stabilized. To this end, geodesics in moduli space are "discretized" by domain walls interpolating between isolated vacua. This picture is connected to renormalization group flows and the information metric via holography, and provides a framework in which geometric properties of the string landscape and constraints on effective field theories can be studied in more realistic settings.
24 October 2023, 14:30
BCFT One-point Functions of Coulomb Branch Operators
I will present our effort to analytically obtain the 1-point functions of chiral operators in N=2 gauge theories in four dimensions, when the theory is placed in the upper half-plane with 1/2-BPS boundary conditions. I will discuss such boundary conditions, along with the complications, and their solutions, for obtaining exact results via localization. As a non-trivial example, I will consider a bulk U(1) theory interacting with the boundary. A closed formula for its 1-point functions will be presented, together with the SL(2,Z)'s action in this set up and, finally, consistency checks also up to non-perturbative regimes (both analytically and via Padé resummations).
17 October 2023, 15:00
Scalar charges and black hole hair
Black holes can have no hair. Scalar charges, which do not seem to obey any conservation law and have no consistent definition, are considered hair. Nevertheless, many black holes seem to have this kind of hair because there are very special values of the scalar charge which seem to be allowed by the no-hair conjecture because they are considered “secondary hair.” It has been argued that these scalar charges play a role in the first law of black-hole mechanics, in spite of their lacking a consistent definition.
In this talk I will propose a consistent definition of scalar charge in stationary black-hole spacetimes which I will use to determine its possible allowed value and formulate no-hair theorems. In order to describe this definition, I will review the definition of conserved charges associated to local and global symmetries in a pedagogical way.constraints on the coupling of the TT̄bar deformation in two dimensions.
26 September 2023, 14:30
Bootstrapping bulk RG flows from the boundary
For QFTs in AdS the boundary correlation functions remain conformal even if the bulk theory has a scale. This property allows one to constrain RG flows with numerical conformal bootstrap methods. We analyze two-dimensional flows between different CFTs with a focus on deformations of the tricritical and ordinary Ising models. We provide non-perturbative constraints for the boundary correlation functions of these flows and compare them with conformal perturbation theory in the vicinity of the fixed points. We also discuss bounds on deformations around arbitrary CFTs, in particular reproducing constraints on the coupling of the TT̄bar deformation in two dimensions.
15 June 2023, 10:00
From scattering amplitudes to gravitational waves
Scattering amplitudes of elementary particles exhibit a fascinating simplicity, which is entirely obscured in textbook Feynman-diagram computations. While amplitudes find their primary application to collider physics, describing the dynamics of the tiniest particles in the universe, they also characterise the interactions among some of its heaviest objects, such as black holes. Violent collisions among black holes occur where tremendous amounts of energy are emitted in the form of gravitational waves, and it is now crucial to develop novel efficient methods for highly needed high-precision predictions. Thanks to their inherent simplicity, amplitudes are ideally suited to this task, but one faces the challenge of extracting classical contributions efficiently.
I will describe how working in a Heavy-mass Effective Field Theory (HEFT) allows to achieve this goal, dropping quantum-suppressed terms and hyper-classical corrections from the get go, i.e. before any integrations are performed. I will then discuss two important applications of the HEFT amplitudes: the computation of the two-loop (or third post-Minkowskian) scattering angle of two spinless black holes; and the determination of the subleading (one-loop) gravitational waveform in the frequency and time domains. These computations are performed using HEFT amplitudes, in conjunction with the Bern-Carrasco-Johansson double copy and generalised unitarity. I will conclude with prospects for future work.
8 June 2023, 14:30
The Witten Diagram Bootstrap for Holographic Defects
We compute correlation functions of two local operators and one defect in holographic conformal field theories. In the supergravity description, the local operators are dual to certain Kaluza-Klein modes, while the defects are dual to probe branes preserving part of the supersymmetry. For concreteness, this talk focuses on correlators of two chiral-primary operator and one Maldacena-Wilson line in N=4 SYM. To obtain the leading strong-coupling correction to this correlator, we make an ansatz in terms of Witten diagrams and fix it with the help of superconformal Ward identities and localization. The result admits a closed-form expression, which takes a surprisingly simple form in Mellin space.
31 May 2023, 14:30