Mathematical Physics Group

The seminars begin at 2.30pm if not stated otherwise.

Oct 9th: Ji Hoon Lee (ETH) - Aula S

Title: AdS3 quantum gravity and finite N chiral primaries 

Abstract: We suggest a bulk explanation for the stringy exclusion principle in AdS3 duals of symmetric orbifold CFTs at finite N. In this context, a sum over one-loop partition functions of an infinite set of bulk geometries that are asymptotic to AdS3 x S3 x T4 or K3 will be shown to reproduce the integer spectrum of chiral primaries in the symmetric orbifold of T4 or K3 at finite N. 

Oct 16th: Ohad Mamroud (SISSA) - Aula C

Title: Branes in the superconformal index 

Abstract: I'll discuss the superconformal index of N=4 SU(N) super Yang-Mills and its holographic interpretation as the partition function of type IIB string theory on AdS_5 x S^5. The latter contains various gravitational saddles, such as Euclidean black holes and orbifolds thereof. It also contains saddles with various SUSY branes on top of these backgrounds. I will identify these contributions within the superconformal index and explain the origin of the branes both in a Cardy-like limit (as eigenvalue instantons) and at large N (as certain continuous solutions in the Bethe Ansatz approach). This understanding allows us to suggest a connection between the branes and the orbifolds, and to better explain the phase diagram of the theory. 

Nov 6th: Claudio Dappiaggi (Pavia U.) - Aula C

Title: Scalar Quantum Field Theory on AdS spacetimes: Boundary conditions and Hadamard states

Abstract: We discuss the quantisation of a real, massive scalar field on the Poincaré patch of an anti–de Sitter (AdS) spacetime. Our goal is twofold. On the one hand, we aim to highlight the role of boundary conditions in the identification of the underlying fundamental solutions and in the construction of Hadamard state, two-point correlation functions with a prescribed singular structure that serve as the building blocks for a covariant formulation of Wick polynomials. On the other hand, we wish to discuss and comment on the open mathematical problems that arise in this setting, in particular by contrasting them with the globally hyperbolic case, where the quantisation procedure and the construction of Hadamard states are by now well understood and under full control.

Nov 13rd: Cristoforo Iossa (Geneva U.) - Aula S

Title: Bouncing off a stringy singularity

Abstract: A sharp signature of black hole singularities in holography is a divergence of the boundary thermal two-point function at a specific point in complex time, arising from a null geodesic bouncing off the singularity. At finite ’t Hooft coupling, stringy corrections modify the bulk dynamics and the fate of this geodesic is an open question. 

We relate these divergences to the analytic structure of the two-point function in momentum space, and propose a simple scenario in which the divergences are smoothed into finite bumps. We illustrate this mechanism explicitly in the Sachdev–Ye–Kitaev model at infinite temperature.

Dec 4th: Alejandro Ruiperez (Rome U. Tor Vergata) - Aula S

Title: Bubbling saddles of the gravitational index

Abstract: I will consider the five-dimensional supergravity path integral that computes a supersymmetric index. Assuming a U(1)^3 isometry, I will report on the recent construction of an infinite family of saddle points with bubbling topology. These are complex finite-temperature configurations asymptotic to S^1 x R^4, which solve the supersymmetry equations. The solutions are characterized by a rod structure specifying the fixed loci of the U(1) isometries and their three-dimensional topology. These fixed loci may correspond to multiple horizons or three-dimensional bubbles, and they may have S^3, S^2 x S^1, or lens space topology.  I will then describe in more detail some physically relevant cases, focusing on configurations with a single horizon and a possibly a bubble just outside of it, which correspond to the saddles associated to extremal BMPV black hole, black ring and black lens. Finally, I will show how the corresponding saddle-point contributions to the gravitational index can be computed very efficiently using equivariant localization, and discuss the resulting thermodynamics. 

Dec 18th: Paolo Arnaudo (University of Southampton) - Aula S

Title: One-loop effective actions and thermodynamics of near-extremal Kerr black holes

Abstract: In this talk, I present an analytic method for performing exact computations of one-loop effective actions in black hole backgrounds. The method is based on a generalisation of the Gelfand-Yaglom formalism to second-order linear ordinary differential equations, where the resulting expressions are governed by the connection coefficients of equations belonging to the Heun class.

As an application, I focus on linear perturbations around Kerr black holes within the Teukolsky formalism, and I present results for the logarithmic corrections to the entropy for massless particles of spin s=1,2. Finally, I briefly discuss the case of Kerr-de Sitter black hole, where different near-extremal configurations can appear.

Jan 29th: Francesco Mignosa (University of Oviedo) - Aula Magna

Title: R-symmetry operators from non-BPS branes 

Abstract: Symmetries play a fundamental role in the study of Quantum Field Theories (QFTs). They provide selection rules, constrain the dynamics of QFTs, and, through anomalies, offer a method to test IR or UV dualities among different QFTs. It is then crucial to understand the symmetries that a theory can enjoy. This recently motivated the study of generalized global symmetries and the description of discrete symmetries through the symmetry Topological Field Theory (symTFT), which separates the symmetry structure from the field theory dynamics. Holography represents a natural laboratory to deal with these aspects: string theory reduced on the internal space of the holographic background realizes the symTFT, and BPS branes describe the charged and topological operators of the dual theory. However, the characterization of continuous symmetry operators in holography is still unclear. 

In this talk, I will briefly review how topological operators implementing continuous symmetries captured by fluctuations of the RR or NSNS gauge fields are realized in terms of non-BPS branes. Then I will extend this concept to R-symmetries, realized as isometries of the internal space of the holographic background, which will be implemented by another non-BPS object, namely a non-BPS KK monopole. I will then apply this general result to the 4d Klebanov-Witten theory. I will review its symmetry Theory (symTh), obtained by reducing supergravity on the dual background, and I will describe how its charged and topological operators and their anomalies are realized by BPS and non-BPS branes respectively, providing a non-trivial check of the proposal. Based on JHEP 02 (2025), 066 with O. Bergman, E. Garcia-Valdecasas, and D. Rodriguez-Gomez, and on  JHEP 10 (2025), 107 with H. Calvo and D. Rodriguez-Gomez. 

Feb 12th: Giulio Bonelli (SISSA) - Aula S

Title: Applied SUSY QFT & BHPT: On one loop corrections to near extremal (dS-)Kerr thermodynamics 

Abstract: 

•The study of Black-Hole perturbation theory [BHPT] is a classical problem in General Relativity and crucial to study gravitational waves etc..

•As the high order of symmetry of the BH gravitational field implies separation of variables, BHPT reduces to the study of 2nd order linear ordinary differential equations (ODE).

•These ODEs have particular rational potentials and are solved exactly by classical Virasoro conformal blocks.

•The latter have an explicit expression because of AGT duality (BPS sector in susy gauge theory ≡CFT2) and the classical limit of crossing relations generate the explicit solution of the connection problem of the ODE.

•Bringing the solution back to BHPT, one gets a powerful computational technique.

•Quantitative and qualitative (exact) results in BHPT: grey-body factors, Love numbers, quasi-normal modes, BH scattering amplitudes, effective actions in BH backgrounds.

•In particular, combining with a generalisation of the Gelfand-Yaglom formula for singular potentials one gets an exact expression for the one loop (dS-)Kerr effective action and a description of the phase diagram of the BH. The universal scaling properties at low Hawking temperature for the near extremal (dS-)Kerr BH are computed and the resulting leading coefficient is shown to coincide with the one computed under the hypothesis that Schwarzian modes only contribute. 

Feb 19th: Pietro Longhi (Uppsala University) - Aula 3 - Time: 11.30

Title: Quiver structures of knot invariants, open strings, and recursion 

Abstract: The knots-quivers correspondence relates HOMFLY-PT polynomials of knots colored by symmetric partitions to motivic Donaldson-Thomas partition functions of symmetric quivers. I will discuss an interpretation of this relation based on string theory, where quivers encode interactions of M2 branes mediated by an M5 brane. Invariance of this picture under deformations leads to a generalization of the knots-quivers correspondence corroborated by wall-crossing type phenomena associated with skein relations among M2 brane boundaries. If time permits, a generalization to multiple M5 branes will be discussed. Based on joint works with Ekholm, Kucharski, Nakamura, and Shende. 

Feb 19th: Andrea Conti (University of Oviedo) - Aula Magna

Title: Defect entanglement entropy for super-(conformal) monodromy defects 

Abstract: Recently, there has been an increasing interest in the study of defects in quantum field theories, with holography providing a powerful framework to explore various aspects of these super-(conformal) gauge theories.

In this talk, I will discuss supergravity solutions that are dual to codimension-2 superconformal monodromy defects. These solutions are obtained using gauged supergravities in D=4,5,6 and 7 dimensions. I will present a prescription to compute the defect entanglement entropy, outlining the renormalization procedure needed to regularise its divergencies. In some cases, we are also able to express this quantity in terms of the free energy/Weyl anomaly of the defect and its conformal weight.

If time allows, I will also discuss some new results for non-conformal monodromy defects.

Mar 5th: Emmanuele Battista (Laboratori Nazionali di Frascati) - Aula Monod

Title: Lorentzian-Euclidean black holes in general relativity

Abstract: We investigate a Schwarzschild-type geometry in which the metric exhibits a signature change across the event horizon, leading to a configuration that we call “Lorentzian-Euclidean black hole”. Since the signature shift can introduce nonstandard distributional behavior at the horizon, we employ the Hadamard partie finie prescription to regularize the geometry.  This technique provides a consistent treatment of otherwise ill-defined expressions and allows us to demonstrate that the resulting geometry satisfies the vacuum Einstein equations in a suitable regularized (weak) sense. We then analyze the geodesic structure of the model. A key result  is that the signature-change mechanism prevents geodesics from reaching the central r=0 singularity.

We conclude by discussing possible observational consequences of such a near-horizon modification and potential signatures that could distinguish the Lorentzian-Euclidean model from the standard Schwarzschild black hole.

The talk is based on:   ArXiv: 2404.17267, 2507.08431 , 2601.10806 

Mar 12th: Alberto Zaffaroni (Università di Milano Bicocca) - Aula Professori

Title: Fortuity in ABJM

Abstract: In recent years the entropy of BPS black holes in AdS has been recovered by counting operators in the dual field theory.

The counting has been done using localization techniques and the explicit form of the operators dual to black hole micro-states is still unknown. 

In the talk I first review the recently introduced concept of fortuity, that could answer to this question, and then I will apply it to the ABJM theory 

and to black holes in AdS4 times S7.

Mar 19th: Matteo Fontana (University of Insubria) - Aula 5

Title: Local Observers in Stationary Axisymmetric Dust Spacetimes 

Abstract: We construct a locally inertial reference system adapted to a geodesic observer in stationary, axisymmetric dust solutions of the Einstein equations employed as effective models of a portion of a galactic disc. To ensure a consistent spatial orientation among different local observers, we also introduce the radially locked reference system, in which one spatial axis is aligned with the radial direction defined by null geodesics passing through the galactic center. Within this framework, we analyze how the dust configuration is described by such observers by computing the frequency shift of photons exchanged between pairs of dust geodesics. Building on this construction, we outline a procedure to reconstruct spectroscopic and astrometric relative velocities with respect to locally inertial observers, providing a coherent foundation for the study of galactic kinematics in a fully general relativistic context. 

Apr 10th: Valentine Maris (ENS de Lyon) - Aula Marro - Time: 11.30

Title: Introduction to noncommutative geometry and deformed quantization 

Abstract: Noncommutative geometry provides a representation of spacetime in terms of associative algebras of operators. The ultimate goal is to arrive at a "quantum spacetime" that encodes quantum gravity effects, at least at an effective level. I will introduce the theory of deformed quantization, which provides tools to build noncommutative spacetimes. Then I will give you an explicit construction of a particular kind of noncommutative spacetimes, which are deformations of Minkowski, and detail their properties.

Apr 16th: Pietro Glorioso (Università di Milano Statale) - Aula Professori

Title: Bethe Ansatz at finite rank: new developments

Abstract: The superconformal index of four-dimensional theories has been widely used to access the microstate counting of a large class of AdS5 black holes. In this framework, the Bethe Ansatz approach has emerged as a powerful technique to compute the index as a sum over vacua. I start by reviewing the main aspects of the Bethe Ansatz method and then I discuss the new results that I have recently obtained. First, I present a low rank analysis of N=1 quiver gauge theories with SU(2) gauge nodes. By inspection I show that a comprehensive study of the index is possible for certain examples (specifically, the conifold and the suspended pinch point singularities). Then, I discuss an ongoing work that aims to generalize these results to the N=2 necklace theories, where new families of Bethe vacua emerge.

Apr 23rd: Palash Jitendra Singh (Università di Milano Bicocca) - Aula Professori

Title: Bad Theories and Distributional Observables in 3d and 5d 

Abstract: We study bad supersymmetric theories with eight supercharges in three and five dimensions. In 3d, these are characterised by sphere

partition functions that are sums of distributions rather than ordinary functions. We identify a distinguished family of bad theories, which we call broken theories, for which the distributional action admits an interpretation as the partial Higgsing of a gauged symmetry. We show that an analogous structure appears in 5d N=1 SCFTs engineered by five-brane webs: suitable nilpotent Higgsings render the superconformal index distributional, and in broken examples its action again admits an interpretation in terms of partial Higgsing. Finally, we connect the 3d and 5d pictures through magnetic quivers. 

May 26th: Anton Galaev (University of Hradec Kralove) - Aula Professori

Title: Holonomy of contact sub-Riemannian manifolds

Abstract: 

The JC internal webpage of can be found here.

The webpage of the season 2024-25 can be found here.

The webpage of the season 2023-24 can be found here.

The webpage of the season 2022-23 can be found here.