String Theory Group at the University of Torino

Defect Central Charges

Conformal defects can be characterised by their contributions to the Weyl anomaly. The coefficients of these terms, often called defect central charges, depend on the particular defect insertion in a given conformal field theory. I will review what is currently known about defect central charges across dimensions, and present novel results. I will discuss many examples where they can be computed exactly without requiring any approximations or limits. These include defects in free theories, and recently developed tools for defects in superconformal field theories.

16th of November 2021, 14:30

Resurgence in TTbar deformed theories: from JT gravity to Yang-Mills.

In this talk, I will consider two examples of TTbar deformed theories and discuss the crucial role played by nonperturbative corrections in the deformation parameter. The first part is dedicated to JT gravity at finite cutoff, as given by its proposed formulation in terms of a deformed Schwarzian quantum mechanics. Resurgence gives a prescription to fix the instantonic terms shaping the spectrum of the theory on arbitrary topologies. The second part is devoted to TTbar deformed two-dimensional Yang-Mills theory. I will show how to extend previous results to any finite value of the gauge rank and how to characterize the rich phase diagram that the theory exhibits for both positive and negative values of the deformation parameter.

9th of November 2021, 14:30

Emergent strings and duality with broken supersymmetry

We explore the dramatic consequences of string-scale supersymmetry breaking. We focus on the USp(32) and U(32) orientifolds of the type IIB and type 0B strings, as well as the SO(16) x SO(16) projection of the exceptional heterotic string, which provide non-tachyonic settings with no moduli directly in ten dimensions. While deceptively innocuous at the level of worldsheet perturbation theory, dynamical gravitational tadpoles backreact on spacetime in a dramatic fashion. We discuss how branes can tame this effect to a certain extent, finding that spacetime universally breaks down at a finite distance, ending in a strongly coupled, highly curved singularity. Remarkably, the dynamics of branes in these settings remains consistent among different complementary regimes despite the absence of supersymmetric protection. We connect the resulting picture with a number of swampland criteria, including the weak gravity, de Sitter and distance conjectures, which are realized via novel mechanisms and provide tantalizing hints for a candidate S-dual heterotic construction of the USp(32) orientifold with “brane supersymmetry breaking”.

19th of October 2021, 14:30

Exact solutions to N=2 D=4 Gauged Supergravity coupled to abelian vector multiplets

Known exact solutions to N=2, D=4 and their properties will be discussed. In particular I will focus on new non BPS solution that consists in a closed universe with two extremal black holes of equal size, surrounding two singularities. They have opposite magnetic charges (and no electric charges), but stay in static equilibrium thanks to the positive pressure of a cosmological constant. The geometry is perfectly symmetric under the exchange of the black holes and the flip of the sign of the charges. However the scalar field is non constant and non symmetric, with different values at the horizons, which depend on a real modulus, remarkably we show that it satisfies the attractor mechanism and the entropy indeed depends only on the magnetic charges. At one of the horizon the solution becomes 1/2-BPS supersymmetric, while at the other one there is no supersymmetry, but the entropy remains independent from the scalar modulus

Sala Fubini

12th of October 2021, 14:30

N=1 inherithed S-duality for oriented quivers

We study necklace quiver gauge theories obtained from type IIA string theory with O-planes. It has been recently observed that such models, that describe different singularities before the projection, become dual after the addition of the O-planes and of the necessary amount of fractional branes, enforcing anomaly cancellations. In this talk we provide the field theory interpretation of this process, in terms of inherited S-duality on the conformal manifold. We then extend the class of conformally S-dual models obtained through orientifold projections and provide further checks of the duality, matching the central charges, the t’ Hooft anomalies and, for low gauge ranks, the superconformal index. We conclude by discussing various extensions and generalizations.

5th of October 2021, 14:30, sala Wataghin

Superconformal theories from S-fold geometries

The term S-folds denotes F-theory compactifications which involve non-trivial S-duality transformations. In this talk I will discuss 4d N=2 preserving S-folds and the worldvolume theories on D3-branes probing them. They consist of two new infinite series of superconformal theories whose distinction lies in the discrete torsion carried by the S-fold and in the difference in the asymptotic holonomy of the gauge bundle on the 7-brane. These models are connected by an interesting web of RG flows and their Higgs branches provide new examples of instanton moduli spaces.

1st of April 2021, 14:30

Radiation in conformal field theories.

We overview recent developments in the study of radiation in conformal field theories. We show that in conformal field theories including scalar fields, the radiative energy density is not positive definite, the radiated power is not Lorentz invariant and it depends on the derivative of the acceleration. We then discuss the coupling dependence of radiation, and we present unified results for conformal field theories with extended supersymmetry by introducing a novel technique which allows us to calculate the Wilson loop and the partition function for these theories. The results we obtain are all-order expressions in the 't Hooft coupling in the planar limit.

1st of December 2020, 14:30

2d (super)gravity and exceptional geometry

Upon torus reduction to two dimensions, (super)gravity theories exhibit an infinite-dimensional group of global symmetries – such as the Geroch group for GR, and E9 for maximal supergravity. These symmetries can be gauged to give rise to more non-trivial dynamics, possibly reflecting flux compactifications on complicated backgrounds. For instance, AdS2 solutions in 2d gauged supergravity may arise from reduction on the compact part of black hole near-horizon geometries. The full structure of these gauged models has so far been elusive and little is known about the flux compactifications leading to them.

I will describe the construction of exceptional field theory for affine Lie algebras, a formalism that promotes the (Geroch/E9) symmetries of 2d (super)gravity to formal invariances of their higher-dimensional parent theories, which greatly simplifies the study of certain classes of flux compactifications and should help us complete the construction of the associated two-dimensional gauged models.

17th of November 2020, 14:30

Quantum extremal islands made easy

Recent discussions of the information paradox involve rather puzzling regions in spacetime called ‘Quantum extremal islands’. We show how these are easily understood from the standard Ryu-Takayanagi formula in the presence of Randall-Sundrum branes in arbitrary dimensions.

10th of November 2020, 14:30

Type B anomalies (Mis-)Matching

In this talk we analyse several aspects related to type B conformal anomalies associated with Coulomb branch operators in 4d N=2 SCFTs. In particular, when the vacuum preserves the conformal symmetry, these anomalies coincide with the two point function coefficients in the Coulomb branch chiral ring. We analyse the behaviour of these anomalies on the Higgs branch, where conformal symmetry is spontaneously broken. We review the argument developed in arXiv:1911.05827 and, following it, we argue that these anomalies are covariantly constant on conformal manifolds. In some cases this can be used to show that the anomalies match in the broken and unbroken phases. Then, in the second part of the talk, we focus on some specific 4d N=2 SCFTs and we test type B anomaly (Mis-)Matching through an explicit Feynman diagram computation. We finally observe that an implication of Type B anomaly Mismatching is the existence of a second covariantly constant metric on the conformal manifold that imposes restrictions on its holonomy group.

3rd of November 2020, 14:30