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25/05/2020, 15:00 — 16:00 — Online

Marcus Berg, *Karlstad University*

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Plane gravitational waves and Jacobi-Maass forms

I will first review the classical Kronecker 2^{nd} limit formula, viewed as a relation between partition functions and Green’s functions in orbifolds of flat space (as discussed for example in arXiv:1407.0027, appendix E). I will then discuss the generalization of this relation to orbifolds of the gravitational plane wave, a Penrose limit of AdS (dual of the BMN limit in gauge theory). This provides a natural one-parameter deformation of Kronecker-Eisenstein series, and more generally of Jacobi-Maass forms. This talk is based on arXiv:1910.02745.

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18/05/2020, 15:00 — 16:00 — Online

Shinji Hirano, *University of the Witwatersrand*

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Random Boundary Geometry and Gravity Dual of $T {\bar T}$ Deformation

We study the random geometry approach to the $T \bar T$ deformation of $2d$ conformal field theory developed by Cardy and discuss its realization in a gravity dual. In this representation, the gravity dual of the $T \bar T$ deformation becomes a straightforward translation of the field theory language. Namely, the dual geometry is an ensemble of $AdS_3$ spaces or BTZ black holes, without a finite cutoff, but instead with randomly fluctuating boundary diffeomorphisms. This reflects an increase in degrees of freedom in the renormalization group flow to the UV by the irrelevant $T \bar T$ operator.

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11/05/2020, 15:00 — 16:00 — Online

Kevin Grosvenor, *University of Wuerzburg*

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Information geometry in quantum field theory: lessons from simple examples

We study the Fisher metrics associated with a variety of simple systems and derive some general lessons that may have important implications for the application of information geometry in holography. Some sample systems of interest are the classical 2d Ising model and the corresponding 1d free fermion theory, the instantons in 3+1d massless phi-fourth theory, and coherent states of free bosons and fermions.

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04/05/2020, 15:00 — 16:00 — Online

Edward Hirst, *University of London*

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Machine-Learning Dessins d'Enfants: Explorations via Modular and Seiberg-Witten Curves

We apply machine-learning to the study of dessins d'enfants. Specifically, we investigate a class of dessins which reside at the intersection of the investigations of modular subgroups, Seiberg-Witten curves and extremal elliptic K3 surfaces. A deep feed-forward neural network with simple structure and standard activation functions without prior knowledge of the underlying mathematics is established and imposed onto the classification of extension degree over the rationals, known to be a difficult problem. The classifications exceeded 0.93 accuracy and around 0.9 confidence relatively quickly. The Seiberg-Witten curves for those with rational coefficients are also tabulated.

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27/04/2020, 15:00 — 16:00 — Online

John McKay, *Concordia University*

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The Monster and its Moonshine Functions

This group of astronomical order is slowly yielding its secrets. It is the symmetry group of a rational conformal field theory. In this introductory talk, I will discuss the functions that constitute monstrous moonshine and explain the importance of the monster group and its connections with better established parts of mathematics.

Video seminar @ Perimeter

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20/04/2020, 15:00 — 16:00 — Online

Gábor Sárosi, *Theory Division CERN*

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Holographic Probes of Inner Horizons

In the context of the AdS/CFT correspondence, charged and rotating thermal ensembles are dual to black holes with inner Cauchy horizons. We argue that an uneventful inner horizon requires certain analytic properties of correlation functions in the dual boundary ensemble which are not consistent with causality and unitarity for charged black holes and rotating black holes in $D>3$. However, they are satisfied for correlators of a holographic $2d$ CFT in a rotating thermal ensemble. This suggests that strong cosmic censorship is enforced in gravity theories with a CFT dual, with the possible exception of the rotating BTZ black hole.

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13/04/2020, 15:00 — 16:00 — Online

Alejandra Castro, *University of Amsterdam*

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The Holographic Landscape of Symmetric Product Orbifolds

I will discuss the application of Siegel paramodular forms to constructing new examples of holography. These forms are relevant to investigate the growth of coefficients in the elliptic genus of symmetric product orbifolds at large central charge. The main finding is that the landscape of symmetric product theories decomposes into two regions. In one region, the growth of the low energy states is Hagedorn, which indicates a stringy dual. In the other, the growth is much slower, and compatible with the spectrum of a supergravity theory on $AdS_3$. I will provide a simple diagnostic which places any symmetric product orbifold in either region. The examples I will present open a path to novel realizations of $AdS_3/CFT_2$.

Video seminar @ Perimeter

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23/03/2020, 15:00 — 16:00 — Room P3.10, Mathematics Building

Gábor Sárosi, *Theory Division CERN*

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Holographic Probes of Inner Horizons

We study the inner horizons of rotating and charged black holes in anti-de Sitter space. These black holes have a classical analytic extension through the inner horizon to additional asymptotic regions. If this extension survives in the quantum theory, it requires particular analytic properties in a dual CFT, which give a prescription for calculating correlation functions for operators placed on any asymptotic boundary of the maximally extended spacetime. We show that for charged black holes in three or greater dimensions, and rotating black holes in four or greater dimensions, these analytic properties are inconsistent in the dual CFT, implying the absence of an analytic extension for quantum fields past the inner horizon. Thus, we find that strong cosmic censorship holds for all AdS black holes except rotating BTZ.

Cancelled due to Covid-19 containment measures.

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02/03/2020, 15:00 — 16:00 — Room P3.10, Mathematics Building

Simon Ross, *Durham University*

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Generalized Gibbs Ensemble and KdV charges in 2d CFTs

2d CFTs have an infinite set of commuting conserved charges, known as the quantum KdV charges. There is a generalised Gibbs ensemble for these theories where we turn on chemical potentials for these charges. I will describe some partial results on calculating this partition function, both in the limit of large charges and perturbatively in the chemical potentials.

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16/12/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

João Caetano, *Simons Center for Geometry and Physics*

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Integrability in and beyond AdS/CFT

In this talk, I am going to review some aspects of the current state of the art of Integrability in the AdS/CFT correspondence and beyond. I will first review a general nonperturbative approach to compute multipoint correlation functions of local operators in the $N=4$ SYM theory which allows us to explore the theory even beyond the planar level. In the second part, I will describe my recent work about exploring deformations of $N=4$ SYM by irrelevant operators, which revives an old attempt of generalizing the AdS/CFT correspondence. Here integrability seems to also play an important role and opens the door for its application for non-conformal field theories.

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09/12/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Paolo Benincasa, *Niels Bohr Institute*

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Understanding $\operatorname{AdS}_2$: From Calogero-like models and SLE to $4d$ black hole microstate entropy

Extremal black holes show the presence of an $\operatorname{AdS}_2$ factor as an universal feature. This fact provides a strong motivation for getting a deeper understanding of $\operatorname{AdS}_2$ spacetimes. In this talk, I will argue how $\operatorname{AdS}_2$ systems have a natural description in terms of $1d$ Calogero-type models and, in turn to SLE curves, which describe the geodesic motion of particles in $\operatorname{AdS}_2$. This treatment allows to compute the dimension of the phase space of these geodesics, linking it to the leading Bekenstein-Hawking black hole entropy and the black hole degeneracy.

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18/11/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Francesca Ferrari, *SISSA Trieste*

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A look into $3d$ modularity

Since the 1980s, the study of invariants of 3-dimensional manifolds has benefited from the connections between topology, physics and number theory. Motivated by the recent discovery of a new homological invariant (corresponding to the half-index of certain $3d$ $N=2$ theories), in this talk I describe the role of quantum modular forms, mock and false theta functions in the study of $3$-manifold invariants. The talk is based on 1809.10148 and work in progress with Cheng, Chun, Feigin, Gukov, and Harrison.

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22/10/2019, 16:00 — 17:00 — Room P3.10, Mathematics Building

Michele Cirafici, *University of Trieste*

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Supersymmetric line operators and their spectral problem

I will discuss BPS invariants associated with quantum line operators in certain supersymmetric quantum field theories. Such operators can be specified via geometric engineering in the UV by assigning a path on a certain curve. In the IR they are described by representation theory data. I will discuss the associated BPS spectral problem and the relevant indices.

Note: unusual date

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27/09/2019, 16:00 — 17:00 — Room P3.10, Mathematics Building

Debashis Ghoshal, *Jawaharlal Nehru University*

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Designing matrix models for zeta functions

The apparently random pattern of the non-trivial zeroes of the Riemann zeta function (all on the critical line, according to the Riemann hypothesis) has led to the suggestion that they may be related to the spectrum of an operator. It has also been known for some time that the statistical properties of the eigenvalue distribution of an ensemble of random matrices resemble those of the zeroes of the zeta function. With the objective to identify a suitable operator, we start by assuming the Riemann hypothesis and construct a unitary matrix model (UMM) for the zeta function. Our approach, however, could be termed *piecemeal*, in the sense that, we consider each factor (in the Euler product representation) of the zeta function to get a UMM for each prime, and then assemble these to get a matrix model for the full zeta function. This way we can write the partition function as a trace of an operator. Similar construction works for a family of related zeta functions.

Note: unusual date

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24/06/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Stefano Andriolo, *Hong Kong University of Science and Technology*

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The Weak Gravity Conjecture

We discuss various versions of the weak gravity conjecture.

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20/05/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Vishnu Jejjala, *University of the Witwatersrand*

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Experiments with Machine Learning in Geometry & Physics

Identifying patterns in data enables us to formulate questions that can lead to exact results. Since many of the patterns are subtle, machine learning has emerged as a useful tool in discovering these relationships. We show that topological features of Calabi–Yau geometries are machine learnable. We indicate the broad applicability of our methods to existing large data sets by finding relations between knot invariants, in particular, the hyperbolic volume of the knot complement and the Jones polynomial.

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07/05/2019, 10:00 — 11:00 — Room P5.18, Mathematics Building

Nils Carqueville, *University of Vienna*

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TQFTS, Orbifolds and Topological Quantum Computation

I will review basic notions and results in topological quantum field theory and discuss its orbifolds, with the aim to apply them in the context of topological quantum computation.

Unusual day and hour and room.

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06/05/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Ceyda Simsek, *University of Groningen*

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Spacetime geometry of non-relativistic string theory

Non-relativistic string theory is described by a sigma model that maps a two dimensional string worldsheet to a non-relativistic spacetime geometry. We discuss recent developments in understanding the spacetime geometry of non-relativistic string theory trying to provide several new insights. We show that the non-relativistic string action admits a surprisingly large number of symmetries. We introduce a non-relativistic limit to obtain the non-relativistic string action which also provides us the non-relativistic T-duality transformation rules and spacetime equations of motion.

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01/04/2019, 15:00 — 16:00 — Room P3.10, Mathematics Building

Davide Masoero, *Faculdade de Ciências, Universidade de Lisboa*

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Meromorphic opers and the Bethe Ansatz

The Bethe Ansatz equations were initially conceived as a method to solve some particular Quantum Integrable Models (IM), but are nowadays a central tool of investigation in a variety of physical and mathematical theories such as string theory, supersymmetric gauge theories, and Donaldson-Thomas invariants. Surprisingly, it has been observed, in several examples, that the solutions of the same Bethe Ansatz equations are provided by the monodromy data of some ordinary differential operators with an irregular singularity (ODE/IM correspondence).

In this talk I will present the results of my investigation on the ODE/IM correspondence in quantum $g$-KdV models, where $g$ is an untwisted affine Kac-Moody algebra. I will construct solutions of the corresponding Bethe Ansatz equations, as the (irregular) monodromy data of a meromorphic $L(g)$-oper, where $L(g)$ denotes the Langlands dual algebra of $g$.

The talk is based on:

- D Masoero, A Raimondo, D Valeri, Bethe Ansatz and the Spectral Theory of affine Lie algebra-valued connections I. The simply-laced case. Comm. Math. Phys. (2016)
- D Masoero, A Raimondo, D Valeri, Bethe Ansatz and the Spectral Theory of affine Lie algebra-valued connections II: The nonsimply-laced case. Comm. Math. Phys. (2017)
- D Masoero, A Raimondo, Opers corresponding to Higher States of the $g$-Quantum KdV model. arXiv 2018.