“QFT, Strings and Beyond”

Spring Semester 2021

Tuesday, 16:00, zoom 940 4378 1498

Organised by: Niklas Beisert, Johannes Broedel, Matthias Gaberdiel, Marc-Antoine Fiset, Pietro Longhi

day
date
time
venue
speaker
title
Tue
23.02.
16:00
zoom 940 4378 1498
Ashoke Sen (Harish-Chandra Research Institute)
“D-instanton amplitudes in string theory”
abstract (click to view) D-instantons give non-perturbative contribution to string theory
amplitudes which can be computed using world-sheet techniques. However the
integrals that appear in this computation often have divergences from
corners of the moduli spaces which cannot be tamed by the usual procedure
of analytic continuation. We show how using insights from string field
theory we can extract finite unambiguous results from these apparently
divergent integrals. (click to hide)
Tue
02.03.
16:00
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Edoardo Lauria (École Polytechnique, CPHT)
“Bootstrappping defect-localized interactions”
abstract (click to view) Is there any room for non-trivial unitary and conformal boundary conditions in the theory of a single free massless scalar field? And what about defects? In this talk I will discuss how the free scalar equations of motion and the structure of the bulk-to-boundary operator expansion lead us to a non-trivial system of crossing equations that we analyze numerically for boundaries in four bulk dimensions. We show that large regions of parameter spaces are excluded, but a ‘kink’ in the numerical bounds obeys all our consistency checks and might be an indication of a new conformal boundary condition. For higher co-dimensions, for example a line defect in three bulk dimensions, these constraints are enough to prove that the only unitary conformal defects are essentially trivial. Based on 2005.02413, 2009.03336 and 2012.07733. (click to hide)
Tue
09.03.
15:45
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Christoph Nega (Bonn)
“Analytic Structure of Banana Feynman Integrals”
abstract (click to view) In this talk I will start with a short motivation why Calabi-Yau varieties and therefrom derived geometric tools are useful in Feynman graph computations. These tools will be exemplified on the so called banana Feynman integrals culminating in understanding their analytic properties, first in two dimensions and then in the dimensional regularization prescription. These Feynman integrals in two dimensions have a natural interpretation as relative periods of a complete intersection Calabi-Yau manifold, whose dimension is the loop order minus one of the banana integral. In particular, we find that the leading logarithmic structure in the high energy regime, which corresponds to the point of maximal unipotent monodromy, is determined by a novel Gamma-class evaluation in the ambient space of the mirror CY and the mirror CY itself. In dimensional regularization we use a Mellin-Barnes and a Bessel function representation of the banana Feynman integral to solve them. I will extend these ideas also shortly to the non-equal mass case which can be described similarly. (click to hide)
Tue
16.03.
16:00
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Ömer Gürdoğan (Southampton)
“From integrability to the coaction properties of Feynman periods”
abstract (click to view) Results in Quantum Field Theories, such as anomalous dimensions or scattering amplitudes are known to exhibit rich properities under the motivic coaction that acts on period integrals. I will show how these phenomena arise directly in an integrability setup describing the anomalous dimensions of a four-dimensional scalar model. (click to hide)
Tue
23.03.
16:00
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Till Bargheer (DESY and Hannover)
“Deconstructing AdS/CFT with integrability”
abstract (click to view) I will describe the integrability-based "hexagonalization" approach to
correlation functions in AdS/CFT, with an emphasis on the connection
between the gauge-theory perturbative expansion and the string-theory
moduli space integral, which is nicely captured by the construction. (click to hide)
Tue
13.04.
14:30
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David Skinner (Cambridge)
“Ambitwistor Strings on AdS3 x S3”
abstract (click to view) Ambitwistor strings are purely chiral worldsheet theories that, in the simplest case, provide a worldsheet description of supergravity. Around flat space, they underpin the CHY description of perturbative scattering amplitudes in terms of scattering equations. In this talk, I’ll construct an anomaly-free ambitwistor string describing supergravity on AdS3 x S3 at the NS point. The problem of computing n-point boundary correlation functions in this theory is transformed into a certain Gaudin integrable system. The scattering equations on AdS3 amount to the statement that all eigenvalues of the SL(2) Gaudin Hamiltonians should simultaneously vanish. (click to hide)
Tue
20.04.
16:00
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Mathew Bullimore (Durham)
“Towards a Mathematical Definition of the 3d Superconformal Index”
abstract (click to view) The aim of this talk is to give a mathematical definition of the superconformal index counting local operators in gauge theories with 3d N = 2 supersymmetry. This can be computed exactly using supersymmetric localisation, which leads to an explicit contour integral formula involving infinite q-Pochhammer symbols. I will explain how this result can be interpreted as the Witten index of a supersymmetric quantum mechanics, or index of a twisted Dirac operator on a certain infinite-dimensional space. To illustrate the essential points, I will focus on a concrete example of supersymmetric Chern-Simons theory. (click to hide)
Tue
27.04.
16:00
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Ana Retore (Trinity College Dublin)
“Constructing new solutions of Yang-Baxter equation”
abstract (click to view) There are several well known integrable models, like Hubbard model, Heisenberg spin chain and various versions of the AdS/CFT correspondence. The main ingredient of an integrable theory is an object called R-matrix which satisfies the so-called Yang-Baxter equation. However, constructing new integrable models can be very complicated. In this talk, I will introduce a new method to find solutions of the Yang-Baxter equation, using the so-called boost operator, and use it to classify R-matrices in various set-ups. Using this method we were able to find several new interesting integrable models, including three deformations of lower dimensional
AdS/CFT S-matrices. (click to hide)
Tue
04.05.
16:00
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Miroslav Rapčák (Berkeley)
“M5-M2 Systems and the Affine Yangian”
abstract (click to view) Representation theory of affine Yangians is known to be closely related to the geometry of branes inside toric Calabi-Yau three-folds. M5-branes wrapping four-cycles give rise to W-algebra-like representations. M2-branes wrapping two-cycles lead to Coulomb-branch-like representations. In my talk, we are going to investigate the system of M2-branes ending on M5-branes. We are going to see a novel interpretation of the free-boson vertex operator, a generalization of the Gaberdiel-Li-Peng "high-wall" modules of the affine Yangian and an algebraic refinement of the relation between Donaldson-Thomas and Pandharipande-Thomas topological vertices. (click to hide)
Tue
11.05.
16:00
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Ida Zadeh (ICTP, Trieste)
“Narain to Narnia”
abstract (click to view) Recently, a new holographic correspondence was discovered between an ensemble average of toroidal conformal field theories in two dimensions and an abelian Chern-Simons theory in three dimensions coupled to topological gravity. I will discuss a generalisation of this duality for three families of conformal field theories and show that the correspondence works for toroidal orbifolds but not for K3/Calabi-Yau sigma-models and not always for the minimal models. For toroidal orbifolds, the holographic correspondence is extended to correlation functions of twist operators by using topological properties of rational tangles in the three-dimensional ball. (click to hide)
Tue
18.05.
16:00
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Brice Bastian (Utrecht)
“Modelling General asymptotic Calabi-Yau Periods”
abstract (click to view) I will discuss an approach to the general study of period vectors of Calabi-Yau threefolds in asymptotic regions of complex structure moduli space. These period vectors play an important role in string compacitifcations, making a better understanding of their general structure desirable. The strategy is to exploit constraints imposed by completeness, symmetry, and positivity, which are formalised in asymptotic Hodge theory. Together with the classification of all possible boundaries in moduli space, these principles allow for a systematic construction of models for the asymptotic period vectors. One also gains insight about the necessity of exponentially suppressed corrections to the polynomial part of the period vector when away from the well-studied large complex structure point. I will also present results for the cases of one- and two-moduli boundaries where this method has been carried out explicitly. (click to hide)
Tue
25.05.
16:00
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André Kaderli (Humboldt and Max Planck Institute)
“Elliptic KZB associator and open-string corrections at genus one”
abstract (click to view) A method to recursively calculate the genus-one, open-string corrections to field-theory amplitudes is presented. For this purpose vectors of iterated integrals satisfying an elliptic Knizhnik-Zamolodchikov-Bernard (KZB) system on the punctured torus are constructed. These vectors interpolate between the genus-zero and genus-one, open-string corrections. The two boundary values, containing the open-string corrections, are related by a representation of the elliptic KZB associator, the generating series of elliptic multiple zeta values. This yields a relation which can be used to calculate genus-one, open-string corrections from the well-known genus-zero, open-string corrections solely using matrix operations of explicitly known matrices. Geometrically, two external states of the (n+2)-point, genus-zero worldsheet are glued together to form an n-point, genus-one worldsheet. (click to hide)

last modified: Mon, 17 May 2021, 08:31 CEST

Fall Semester 2021

Tuesday, 14:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Matthias Gaberdiel, Marc-Antoine Fiset, Pietro Longhi

day
date
time
venue
speaker
title
Wed
22.09.
14:00
HIT E41.1
Nana Cabo Bizet (Universidad de Guanajuato)
“The geometry of gauged linear sigma models and T-duality”
abstract (click to view) Mirror symmetry constitutes a correspondence between two different Calabi-Yau varieties M and W, such that compactifications of type IIA and type IIB string theory on them, give rise to equivalent physics. The gauged linear sigma models (GLSM) constitute an UV description of the string world-sheet theory. Abelian T-duality in GLSMs has been proven to be equivalent to mirror symmetry. We construct non-Abelian T-dualities in GLSMs, exploring the geometry of the dual models. We discuss the duality for a supersymmetric (2,2) GLSM whose vacuum is given by the deformed conifold. This is a model with SU(2)xSU(2) global symmetry which is gauged to obtain a Lagrangian that allows to interpolate between dual models. These dualities give rise to new physical equivalences. (click to hide)
Tue
28.09.
14:00
HIT E41.1
Marius Gerbershagen (Universität Würzburg)
“Generalized entanglement measures in AdS3/CFT2”
abstract (click to view) In the AdS/CFT context, generalized entanglement refers to an entanglement measure that takes into account not only quantum correlations between between spatial degrees of freedom, but also between different fields of the theory. In this talk, I will explain how to define one such entanglement measure in AdS3/CFT2 that is dual to the length of a geodesic winding around a naked singularity or black hole horizon. I will discuss the computation of this quantity for pure states dual to conical defects and thermal states dual to BTZ black hole backgrounds in the D1/D5 system at the orbifold point as well as subtleties regarding its gauge invariant definition. Finally, I will comment on deformations away from the orbifold point and consequences for the reconstruction of the bulk geometry in terms of boundary data. (click to hide)
Tue
05.10.
14:00
HIT E41.1
Tommaso Macrelli (ETH)
“Colour-kinematic duality, double copy and homotopy algebras”
abstract (click to view) While colour-kinematic duality and double copy are a well established paradigm at tree level, their loop level generalisation remained for a long time an unsolved problem. Lifting the on-shell, scattering amplitude-based description to an action-based approach, we show that a theory that exhibits tree level colour-kinematic duality can be reformulated in a way such that its loop integrands manifest colour-kinematic duality.
With Yang-Mills theory as our main example, we provide a theoretical toolkit for systematically producing a loop level colour-kinematic duality manifesting action from a theory with colour-kinematic-dual tree level scattering amplitudes. Finally, we discuss an interpretation of colour-kinematic duality and double copy in terms of homotopy algebras, introducing an adequate notion of colour-kinematic factorisation.
This talk is based on arXiv:2007.13803 [hep-th], arXiv:2102.11390 [hep-th], arXiv:2108.03030 [hep-th]. (click to hide)
Tue
19.10.
17:00
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Grant Remmen (UCSB)
“Amplitudes and the Riemann Zeta Function” (UNUSUAL TIME)
abstract (click to view) In this talk, I will connect physical properties of scattering amplitudes to the Riemann zeta function. Specifically, I will construct a closed-form amplitude, describing the tree-level exchange of a tower with masses m^2_n = \mu^2_n, where \zeta(\frac{1}{2}\pm i \mu_n) = 0. Requiring real masses corresponds to the Riemann hypothesis, locality of the amplitude to meromorphicity of the zeta function, and universal coupling between massive and massless states to simplicity of the zeros of \zeta. Unitarity bounds from dispersion relations for the forward amplitude translate to positivity of the odd moments of the sequence of 1/\mu^2_n (click to hide)
Tue
26.10.
14:00
HIT E41.1
Albrecht Klemm (Universitat Bonn)
“Feynman Integrals in Dimensional Regularization and Extensions of Calabi-Yau Motives”
abstract (click to view) We provide a summary of concepts from Calabi-Yau motives relevant to the computation of multi-loop Feynman integrals. From this we derive several consequences for multi-loop integrals in general, and we illustrate them on the example of multi-loop banana integrals. For example, we show how Griffiths transversality, known from the theory of variation of mixed Hodge structures, leads quite generically to a set of quadratic relations among maximal cut integrals associated to Calabi-Yau motives. These quadratic relations then naturally lead to a compact expression for $l$-loop banana integrals in $D=2$ dimensions in terms of an integral over a period of a Calabi-Yau $(l-1)$-fold. This new integral representation generalizes in a natural way the known representations for $l\le 3$ involving logarithms with square root arguments and iterated integrals of Eisenstein series. We show how the results can be extended to dimensional regularization. We present a method to obtain the differential equations for banana integrals with an arbitrary number of loops in dimensional regularization without the need to solve integration-by-parts relations. We also present a compact formula for the leading asymptotics of banana integrals with an arbitrary number of loops in the large momentum limit that generalizes the $\widehat{\Gamma}$-class formalism to dimensional regularization and provides a convenient boundary condition to solve the differential equations for the banana integrals. As an application, we present for the first time numerical results for equal-mass banana integrals with up to four loops and up to second order in the dimensional regulator. (click to hide)
Tue
26.10.
15:00
HIT E41.1
Michael Borinsky, Johannes Broedel, Albrecht Klemm
“From Feynman graphs to Calabi-Yau manifolds” (Block seminars 3pm-6pm)
Wed
27.10.
14:00
HIT E41.1
Michael Borinsky, Johannes Broedel, Albrecht Klemm
“From Feynman graphs to Calabi-Yau manifolds” (Block seminars 2pm-6pm)
Wed
03.11.
14:00
HIT E41.1
Lorenzo Bianchi (Università di Torino)
“A Page curve from boundary quenches” (UNUSUAL DAY)
abstract (click to view) In light of the recent progress in understanding the black hole information paradox, we consider a local quench in a boundary conformal field theory and study the entropy of the emitted radiation. We show that the real time evolution has the features of a Page curve (the entropy grows at early time and decays at late time). We provide a general upper bound on the late time behaviour of the entanglement entropy and we show that this bound is saturated by the holographic result. We conclude by commenting on how this setup is related to black hole radiation. (click to hide)
Tue
09.11.
14:00
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Leron Borsten (Heriot-Watt University, Edinburgh)
“On colour-kinematic duality and the double copy”
abstract (click to view) We begin by reviewing the colour-kinematics duality of (super) Yang-Mills theory and its double copy into (super)gravity. We then show that off-shell colour-kinematics duality can be made manifest in the Yang—Mills Batalin—Vilkovisky action, up to Jacobian counter-terms. The latter imply a departure from what is normally understood by colour-kinematics duality in that the counterterms generically break it. However, this notion of CK duality is very natural and, most importantly, implies the validity of the double copy to all orders in perturbations theory. We then describe generalisations to the non-linear sigma model and super Yang-Mills theory, where Sen’s formalism for self-dual field strengths emerges automatically. We conclude by discussing the mathematical underpinnings of these observations in terms of Homotopy algebras. Figuratively, colour-kinematics duality is a symmetry of Yang—Mills in the same sense that a mug is a donut. (click to hide)
Tue
16.11.
14:00
zoom 62452289765
Roberto Ruiz Gil (Universidad Complutense de Madrid)
“Wess-Zumino-Novikov-Witten spin-chain σ-models”
abstract (click to view) In this talk, I shall present the spin-chain σ-model of the Wess-Zumino-Novikov-Witten (WZNW) model that realises bosonic strings on AdS3 x S3 with pure Neveu-Schwarz-Neveu-Schwarz flux. I shall begin with a review of developments made in the AdS5/CFT4 correspondence on the basis of spin-chain σ-models. I shall then focus on spin-chain σ-models for the SL(2,R) and SU(2) WZNW models. I shall present their construction from both a semi-classical limit in the classical action and a Landau-Lifshitz limit in the underlying integrable spin chain. I shall finish by commenting on open problems. (click to hide)
Tue
23.11.
14:00
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Elli Pomoni (DESY)
“Dynamical spin chains in 4D N = 2 SCFTs”
abstract (click to view) In this talk we will revisit the study of spin chains capturing the spectral problem of 4d N = 2 SCFTs in the planar limit. At one loop and in the quantum plane limit, we will discover a quasi-Hopf symmetry algebra, defined by the R-matrix read off from the superpotential. This implies that when orbifolding the N = 4 symmetry algebra down to the N = 2 one and then marginaly deforming, the broken generators are not lost, but get upgraded to quantum generators. Thereafter, we will demonstrate that these chains are dynamical, in the sense that their Hamiltonian depends on a parameter which is dynamically determined along the chain. At one loop we will show how to map the holomorphic SU(3) scalar sector to a dynamical 15-vertex model, which corresponds to an RSOS model, whose adjacency graph can be read off from the gauge theory quiver/brane tiling. One scalar SU(2) sub-sector is described by an alternating nearest-neighbour Hamiltonian, while another choice of SU(2) sub-sector leads to a dynamical dilute Temperley-Lieb model. These sectors have a common vacuum state, around which the magnon dispersion relations are naturally uniformised by elliptic functions. For the example of the SU(N)xSU(N) quiver theory we will study these dynamical chains by solving the one- and two-magnon problems with the coordinate Bethe ansatz approach. (click to hide)
Tue
30.11.
14:00
HIT E41.1
Carlo Maccaferri (Università di Torino)
“Background Independence of Open String Field Theory”
abstract (click to view) I review the recent construction of analytic classical solutions of open string field theory (OSFT) which describe any boundary conformal field theory (BCFT) as a solution of the OSFT defined on any other BCFT. This establishes that all D-branes are open string solitons of the same space-time theory. The theory of fluctuations on the classical solution can be related to the OSFT directly defined on the new D-brane system by integrating out certain pure gauge degrees of freedom and then by performing a simple field redefinition. I give an explicit construction of this integration-out via a novel application of the homotopy transfer in the framework of the homological perturbation lemma. (click to hide)
Tue
07.12.
14:00
zoom 62452289765
David Tennyson (Imperial College London)
“Topological strings at 1-loop from double complexes”
abstract (click to view) The topological A/B-model have been important tools for studying both string theory and the geometry of Calabi-Yau manifolds. They provide both new geometric invariants of the Calabi-Yau, as well as calculating certain terms in the effective theory of string theory. While topological strings on other special holonomy manifolds have been postulated, they are far less understood. In my talk, I will examine the topological string on G2 and Spin(7) manifolds from the target space perspective. I will show that any special holonomy manifold has a double complex which generalises the Dolbeault complex of Calabi-Yau manifolds and provides the natural candidate for the BRST complex of the topological string. Through this, I will be able to conjecture the cohomology of operators and the 1-loop partition functions of the G2 and Spin(7) topological strings. (click to hide)

last modified: Mon, 6 Dec 2021, 15:04 CET

Spring Semester 2022

Tuesday, 14:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Matthias Gaberdiel, Marc-Antoine Fiset, Francesco Galvagno

day
date
time
venue
speaker
title
Tue
01.03.
14:00
HIT E41.1
Ondřej Hulík (Vrije U., Brussels)
“G-Algebroids: a unified framework for exceptional and generalized geometry”
abstract (click to view) I will describe the concept of G-algebroid, which generalizes both Lie and
Courant algebroids, as well as the Leibniz algebroids used in the
description of exceptional generalized geometry. I will discuss a
classification results and possible applications of G-algebroids in
formulating Poisson-Lie U-duality. The talk is based on a joint work with
Mark Bugden, Fridrich Valach and Daniel Waldram. (click to hide)
Tue
08.03.
14:00
HIT E41.1
Marco Gualtieri (U. of Toronto)
“Recent advances in the geometry of the N=(2,2) supersymmetric 2-dimensional sigma model”
abstract (click to view) I will explain some of the more intriguing recent developments in Generalized Kähler geometry, the general target space geometry of 2-dimensional sigma models with (2,2) supersymmetry. We will focus on the unexpected way that the Kähler potential function arises in the general case, and how this leads, through quantization, to a surprising relation with noncommutative algebraic geometry. (click to hide)
Tue
15.03.
14:00
Zoom: 669 6805 3963
Dalimil Mazáč (Institute for Advanced Study)
“Bootstrapping Boundaries and Branes”
abstract (click to view) I will discuss bootstrap constraints on conformal boundary conditions in 2D CFTs. In particular, I will explain how to derive bounds on the boundary entropy starting from the consistency of the annulus partition function. In the context of string theory, these imply a universal upper bound on the tension of stable D-branes. It turns out that our bounds are often saturated by interesting boundary conditions in rational CFTs. In some cases, the exact saturation can be proven using analytic functionals, which is closely related to the solution of the sphere packing problem in 8 and 24 dimensions. Our bounds at large central charge have potential implications for end-of-the-world branes in pure gravity on AdS_3. The talk will be based on https://arxiv.org/pdf/2112.00750.pdf, which is joint work with Scott Collier and Yifan Wang. (click to hide)
Tue
22.03.
14:00
Zoom: 669 6805 3963
Eduardo Casali (Harvard U.)
“Celestial OPE from twistor strings”
abstract (click to view) Celestial conformal field theory (CCFT) is a conjectured theory living on the celestial sphere of the asymptotic boundary of Minkowski. In analogy to the usual AdS/CFT dictionary, CCFTs would be dual to gravitational theories in the bulk, with bulk scattering amplitudes being dual to correlation functions on the celestial sphere. OPE coefficients are basic building blocks of CFTs which should also have an analogue in CCFTs. It has been shown that CCFT OPEs can be extracted from amplitudes with appropriate wavefunctions for external states, but there's still no direct computation using the CCFT itself since we lack a first principles definition. I will talk about recent work I have done computing these OPEs directly by using twistor strings, circumventing the issue of the target space theory. I will show how the worldsheet CFT of the twistor string gives a realization of the algebra of operators of the CCFT, reproducing the known leading OPE terms, as well as how it can be used to compute further regular terms in the OPE, beyond what is currently known. As a bonus, the worldsheet OPE also organizes the spectrum naturally in terms of the infinite dimensional symmetry algebras of CCFTs. (click to hide)
Tue
29.03.
14:00
Zoom: 669 6805 3963
Gabriel Larios (Madrid, IFT and Michigan U., LCTP)
“Lessons and surprises from Kaluza-Klein spectra”
abstract (click to view) Infinite towers of massive modes arise for every compactification of higher dimensional theories. Understanding the properties of these Kaluza-Klein towers on non-trivial solutions with an AdS factor has been a longstanding issue with clear holographic interest, as they describe the spectrum of single-trace operators of the dual CFTs at strong coupling and large N. In this talk, I will focus on two classes of solutions of such kind. The first class consists of AdS4 S-fold solutions of Type IIB supergravity that can be obtained from maximal gauged supergravity in D=4. For the latter part, I will describe new families of solutions in N=(1,1) supergravity in D=6 which uplift from half-maximal supergravity in D=3. In both cases, the spectra can be computed using recent techniques from Exceptional Field Theory, and the information thus obtained leads to several questions from the CFT side and unexpected conclusions. (click to hide)
Tue
05.04.
14:00
HIT E41.1
Gabriel Cuomo (Stony Brook U., New York)
“Taxonomy of Wilson lines”
abstract (click to view) I will discuss some results on the space of Wilson lines in
conformal (and quasi-conformal) gauge theories. I will first discuss 4d
theories, focussing on the illustrative examples of massless scalar and
fermionic QED. I will show in particular that lines with sufficiently large
charge are subject to an instability towards charge screening from matter
fields. I will discuss the physical consequences of this instability and
its relation with a novel class of Wilson lines. Similar results apply in
nonAbelian conformal gauge theories, such as N = 4 SYM. I will finally
mention the generalization of these results to 3d conformal gauge theories,
and discuss possible applications in condensed matter systems. Based on a
work in progress with Ofer Aharony, Zohar Komargodski, Ma ́rk Mezei and
Avia Raviv-Moshe. (click to hide)
Tue
12.04.
14:00
HIT E41.1
Federico Zerbini (IPhT (CEA-Saclay))
“String amplitudes, polylogarithms and KZB connections”
abstract (click to view) The perturbative expansion of string theory amplitudes is an important testing ground for double-copy relations between gravity and gauge theories, and the AdS/CFT correspondence. It is indexed by an integer which can be interpreted as the genus of a surface. In the last decade, the combined effort of mathematicians and physicists led to great progress in our understanding of the genus-zero and genus-one coefficients. I will report on this progress, with special focus on the role of Knizhnik-Zamolodchikov-Bernard (KZB) connections, which arise from Wess-Zumino-Witten models, and of polylogarithm functions. At the end I will report on higher-genus perspectives, based on a joint work with Benjamin Enriquez. (click to hide)
Tue
03.05.
14:00
HIT E41.1
Shota Komatsu (CERN)
“Large Charge and Coulomb Branch of N=4 SYM”
abstract (click to view) We explore the relationship between the large charge sector and
the Coulomb branch of N=4 super-Yang-Mills (SYM) both in the large N limit
and in a theory with the SU(2) gauge group. In particular, we propose
concrete formulae relating the correlation functions of the large charge
operators and the correlation functions on the Coulomb branch and discuss
their interplay with the OPE and the form factor expansion. We also argue
that the spectrum of non-BPS operators in the large charge sector of N=4
SYM with the SU(2) gauge group is governed by the centrally-extended
SU(2|2) symmetry---the symmetry which played a crucial role in the analysis
of the large N limit. (click to hide)
Tue
17.05.
14:00
HIT E41.1
Andrew Mcleod (CERN)
“A Three-Point Form Factor through Eight Loops, and a New Form Factor/Amplitude Duality”
abstract (click to view) Traditional methods for computing quantities such as scattering amplitudes and form factors in quantum field theory become intractable at high perturbative orders. However, a great deal is now known about the mathematical properties of these quantities, especially in supersymmetric gauge theories. In this talk, I will describe how this knowledge can be leveraged to 'bootstrap' amplitudes and form factors directly, by constructing an ansatz with the appropriate mathematical structure and requiring it to have certain expected behavior in special kinematic limits. I will focus on the example of three-point form factors in maximally supersymmetric gauge theory, which have recently been bootstrapped through eight loops. I will then describe a remarkable new duality between this form factor and certain six-particle amplitudes in the same theory, which holds order by order in perturbation theory. (click to hide)
Tue
24.05.
14:00
Zoom: 669 6805 3963
Silvia Nagy (Queen Mary, U. of London)
“Different approaches to gravity from Yang-Mills squared”
abstract (click to view) The idea of writing various quantities in gravity as double copies of the analogous objects in Yang-Mills gauge theory has been gaining a lot of traction in recent years - I will give an overview of the numerous different formulations that have arisen from this drive. Then I will focus on 2 particular ones: the first is based on certain double copy replacement rules in the self-dual sector, and the second links with twistor theory. These have allowed for a recent expansion of the remit of the double copy in the context of symmetries and classical solutions. Finally, I will make some comments on a more ambitious question: is it possible to unify the various different formulations into a single framework? (click to hide)
Tue
31.05.
14:00
HIT E41.1
Ben Hoare (Durham U.)
“Integrable deformations of Z2 and Z4 permutation cosets”
abstract (click to view) Integrable 2d sigma models on Z2 and Z4 permutation cosets, with G x G symmetry group, describe strings on AdS3 space-times. The product structure of the symmetry group leads to a richer space of integrable deformations. In this talk I will outline recent progress in mapping out this space, before discussing a special class of deformations of AdS3 x S3 x T4 that preserve half the supersymmetry. Interestingly, these deformations can either be found via Yang-Baxter deformations, proving their integrability, or by U-duality transformations. (click to hide)
Tue
07.06.
11:30
HIT E41.1
Jnan Maharana (Institute of Physics, Bhubaneswar)
“Is the scattering amplitude analytic in a field theory with a compact spatial coordinate?”
abstract (click to view) N.N. Khuri, in 1995, investigated analytcity property of scattering
amplitude in potential scattering where one spatial dimension was
compactified on a circle of radius R. He showed that the forward
scattering amplitude, in this case does not satisfy dispersion relations
whereas in potentials without a compact coordinate the amplitude is
analytic, known for a long time. If this result were valid for a
relativistic QFT with a compact spatial coordinate then it will be
a matter of serious concern. I consider a massive scalar field theory in flat
5-dimensional space and then compactify one spatial cordinate on a circle.
I employ LSZ formalism and show that forward scattering amplitude satisfies
dispersion relations. Properties of nonforward amplitude are discussed
which goes beyond Khuri's result. Possible consequences of decompactification
at LHC energies will be discussed. (click to hide)

last modified: Wed, 1 Jun 2022, 09:24 CEST

Autumn Semester 2022

Wednesday, 15:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Matthias Gaberdiel, Francesco Galvagno

day
date
time
venue
speaker
title
Thu
06.10.
11:00
Zoom: 384 022 1288
Takuya Matsumoto (Nagoya University)
“Drinfeld realization of the centrally extended psl(2|2) Yangian algebra with the manifest coproducts”
abstract (click to view) The Lie superalgebra psl(2|2) is recognized as a pretty special one in
both mathematics and theoretical physics.
In this talk, I will propose the Drinfeld realization of the Yangian
algebra associated with the centrally extended Lie superalgebra
psl(2|2).
Furthermore, I show that it possesses the Hopf algebra structures,
particularly the coproducts.
The idea to prove the existence of the manifest coproducts is the following.
Firstly, I shall introduce them to Levendorskii's realization, a
system of a finite truncation of the Drinfeld generators.
Secondly, I show that Levendorskii's realization is isomorphic to the
Drinfeld realization by induction.
If time allows, I would like to mention the related topics and some
future directions.
This work is based on the preprint [arXiv:2208.11889 [math.QA]]. (click to hide)
Wed
12.10.
15:00
HIT E41.1
Hynek Paul (IPHT Saclay)
“Integrated Correlators in N=4 SYM via SL(2,Z) Spectral Theory”
abstract (click to view) I will describe the computation of integrated four-point correlation functions of half-BPS operators in N=4 SYM with gauge group SU(N). We focus on correlators of the form <22pp>, which are computable by supersymmetric localisation and yet are non-trivial functions of the complexified gauge coupling \tau. By employing the SL(2,Z) spectral decomposition, we find explicit and remarkably simple results for these observables, exactly as a function of N and \tau. They turn out to be polynomials in the spectral parameter, obeying linear algebraic equations relating different N and p. Our results include the full matrix of integrated correlators at low values of p as well as a certain infinite class involving operators of arbitrary p. Based on [https://arxiv.org/abs/2209.06639]. (click to hide)
Wed
19.10.
15:00
HIT E41.1
Laurentiu Rodina (Queen Mary University of London)
“The geometry of EFT and CFT”
abstract (click to view) The space of EFT couplings and 2D CFT partition functions can be described by identical geometries. I will present an analytical approach that allows one to include constraints which so far have been less explored, such as the unitarity upper bound (for EFT) and degeneracy integrality (for CFT). These lead to interesting reductions in allowed theory space. (click to hide)
Wed
26.10.
15:00
HPL D32
Anthony Houppe (IPHT Saclay)
“Non-BPS microstate geometries and holography”
abstract (click to view) The correspondence between heavy states of the D1-D5 orbifold CFT and classical supergravity solutions asymptotic to AdS3 x S3 is well established for a large number of BPS states. This dictionary is however poorly understood for non-BPS states, because of the difficulty of generating non-supersymmetric solutions in the bulk, and because the matching of these solutions with CFT states is complicated by the absence of protected operators. In this talk I will review the construction of non-BPS, asymptotically-AdS supergravity solutions that are microstates of the D1-D5-P system, whose CFT duals can remarkably also be identified. (click to hide)
Wed
02.11.
15:00
HIT E41.1
Fabio Apruzzi (Bern University)
“Non-Invertible Symmetries from Holography and Branes”
abstract (click to view) Generalised non-invertible symmetries have emerged in the past year as a new type of symmetry in d≥ 4 QFTs. This has lead to a new understanding of certain constraints on the dynamics of QFTs, such as QED. In this talk I will describe a systematic approach to deriving symmetry generators of Quantum Field Theories in holography. Central to this are the Gauss law constraints in the Hamiltonian quantization of Symmetry Topological Field Theories (SymTFTs), which are obtained from supergravity. Crucially we also realize the symmetry generators from world-volume theories of D-branes in holography. I will particularly focus on non-invertible symmetries, by presenting the application of our proposal in the holographic setup, dual to 4d N=1 SU(M) or PSU(M) Super-Yang Mills (SYM). In the brane-picture, the fusion of non-invertible symmetries naturally arises from the Myers effect on D-branes. In addition the action of the topological non-invertible defects t’Hooft on line is modeled by the Hanany-Witten effect. For SU and PSU SYM, we also identify the infra-red (IR) 4d field theory rom the dual gravity description, which describe the domain-walls and confining/deconfining behaviour in the IR. (click to hide)
Thu
10.11.
11:30
HIT E41.1 and Zoom: 384 022 1288
Tim Adamo (University of Edimburgh)
“Graviton scattering and hyperkähler geometry”
abstract (click to view) From the perspective of traditional perturbation theory, the computation of gravitational scattering amplitudes is a nightmare, as the non-linearities of general relativity induce an infinite number of Feynman rules. Yet in recent years, remarkably compact formulae for tree-level graviton scattering have been discovered whose origins in general relativity are obscure. I will discuss how these expressions can be derived from first principles using the interplay between perturbative general relativity, hyperkähler geometry and twistor theory. This perspective also enables new calculations for gravitational scattering in curved space-time that are not accessible with other approaches. (click to hide)
Wed
16.11.
15:00
HIT E41.1
Davide Bufalini (Southampton University)
“Microstate correlators from the worldsheet”
abstract (click to view) To account for all the bulk microstates of a three-charge black hole, the supergravity approximation may not suffice and full control over string theory may be essential.
Recently, a specific family of black hole microstates was shown to admit an exact string worldsheet description. The worldsheet theory is a coset of the well-studied AdS3xS3xT4 model. This allows full control over the entire alpha' corrections.
I will show how to construct the physical vertex operators of these coset models, and how to explicitly compute an extensive set of novel heavy-light correlators. Finally, I will present a closed formula for correlators with an arbitrary number "n" of light insertions on top of the microstate background, written as a function of the corresponding n-point function on pure AdS3xS3xT4.
A subset of these provides the first match between worldsheet correlators in black hole microstates and the holographically dual conformal field theory, in a highly non-trivial way. (click to hide)
Wed
23.11.
15:00
HIT E41.1
Sibylle Driezen (Santiago de Compostela University)
“Integrable deformations and dualities of string sigma-models”
abstract (click to view) In this talk, I will review recent work on deformations and generalised
T-dualities which preserve the integrability of string sigma-models. As a
guiding exemplar, I will focus on the so-called Homogeneous Yang-Baxter
deformations, which are a class of deformations that interpolate between a
sigma-model and its non-abelian T-dual. As a special case they capture the
well-known TsT-transformations involving standard abelian T-duality. At the
level of the low-energy string as well as worldsheet integrability it has
been understood that many of the attractive features of TsT carry over to
the generalised Yang-Baxter case. Using the framework of Double Field
Theory, I will first show how one can easily understand Yang-Baxter
deformations as solution-generating techniques of supergravity, and I will
argue how a large web of transformations with the same feature can be more
generally classified. At the same time, these transformations can be
understood as canonical transformations of the worldsheet. I will show in
the Yang-Baxter case how this implies that they can be equivalently
described on-shell in terms of a twisting of the worldsheet boundary
conditions of the undeformed model. This feature makes it particularly
efficient to employ integrable methods such as the classical spectral curve
and its semi-classical quantisation to obtain energy corrections, and thus
opens a route to study integrable deformations of AdS/CFT. I will report on
progress obtained for a Homogeneous Yang-Baxter deformation of the AdS5 x
S5 superstring. (click to hide)
Wed
30.11.
15:00
HIT E41.1
Cristian Vergu (Niels Bohr Institute)
“On-shell spaces, critical points and singularities of amplitudes”
abstract (click to view) I will discuss singularities of amplitudes from the point of view of critical points of projection maps between on-shell spaces. The simplest type of critical values, called $S_1^+$, are of codimension one and such that the Hessian around the critical value is positive or negative definite. For such singularities one can write (by an application of Picard-Lefschetz theorem) the discontinuity as a Cutkosky integral, which can itself be analyzed by the same methods. This provides a framework for discussing the compatibility of a large class of singularities thus generalizing the Steinmann relations. (click to hide)
Wed
07.12.
15:00
HIT E41.1
Stephan Stieberger (Munich, Max Planck Institute)
“Elements of Celestial Conformal Field Theory”
abstract (click to view) I will introduce into subject of holographic description of four-dimensional massless physics
as conformal field theory on the celestial sphere and report on progress on celestial conformal field theory (CCFT).
In celestial holography, four-dimensional scattering amplitudes are considered as two-dimensional conformal correlators of a putative two-dimensional CCFT. The simplest way of converting momentum space amplitudes into CCFT correlators is by taking their Mellin transforms with respect to light-cone energies. For massless particles, like gluons, however, such a construction leads to three-point and four-point correlators that vanish everywhere except for a measure zero hypersurface of celestial coordinates. This is due to the four-dimensional momentum conservation law that constrains the insertion points of the operators associated with massless particles. These correlators are reminiscent of Coulomb gas correlators that, in the absence of background charges, vanish due to charge conservation. We supply the background momentum by coupling Yang-Mills theory to a background dilaton field, with the (complex) dilaton source localized on the celestial sphere. We show that the celestial Yang-Mills amplitudes evaluated in the presence of a spherical dilaton shockwave are given by the correlation functions of primary field operators factorized into the holomorphic current operators times the "light" Liouville operators. They are evaluated in the semiclassical limit of Liouville theory (the limit of infinite central charge) and are determined by the classical Liouville field describing metrics on the celestial sphere. (click to hide)
Wed
14.12.
15:00
HIT E 41.1 and Zoom: 384 022 1288
Daniel Thompson (Swansea University)
“Aspects of chiral dynamics and resurgence in E-models”
abstract (click to view) This is a talk in two parts. A variety of integrable sigma models can be interpreted as ${\cal E}$ models; a first order description with chiral currents defined on a group manifold of double the dimension of the sigma target space. I will outline some recent developments of topological aspects of these the theories. I will further move on to review Severa's construction of these ${\cal E}$ models as boundary dynamics of 3d Chern Simons which will allow us to make some novel remarks on the treatment of Lorentz invariant formulations of chiral dynamics. In the second part of the talk, I will describe recent emerging findings of the resurgent structure of lambda deformations giving a snapshop into the asymptotic behaviour of an asymptotic CFT. (click to hide)
Tue
31.01.
14:00
HIT E41.1
Shruti Paranjape (University of California, Davis)
“Non-Planar Geometries from Tree-Level Superymmetric Yang-Mills”
abstract (click to view) The special structure of interactions in maximally supersymmetric Yang-Mills (SYM) allows us to construct certain scattering amplitudes on-shell. Most known geometric constructions work for N=4 SYM in the planar limit. In this talk, we make a first step towards non-planar SYM. To do this, we express tree-level amplitudes as a sum of "non-planar" contributions. These non-planar puzzle pieces appear on unitarity cuts of non-planar loop integrands. We give a nice geometric interpretation of these terms and discuss the extension of these non-planar geometries to more general cases, including a possible extension to theories of gravity. (click to hide)

last modified: Mon, 30 Jan 2023, 21:27 CET

Spring Semester 2023

Wednesday, 14:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Matthias Gaberdiel, Francesco Galvagno

day
date
time
venue
speaker
title
Wed
22.02.
14:00
HIT E41.1
Brian McPeak (University of Pisa)
“Bounding EFTS with gravity”
abstract (click to view) In this talk, I will review recent methods for deriving two-side bounds on EFT coefficients using dispersion relations. In the presence of gravity, the so-called "t-channel pole" invalidates the simplest methods for deriving such bounds, so I will explain how smeared functionals allow for the derivation of bounds in EFTs with gravity. Applications to be discussed will include photon scattering and the weak gravity conjecture, as well as EFTs for massive vectors and gravitons. (click to hide)
Wed
01.03.
14:00
HIT E41.1
Ivano Basile (Munich, Max Planck Institute)
“Dark energy & braneworlds”
abstract (click to view) Model building based on string compactifications faces difficult
challenges: moduli can be tricky to stabilize, scales to separate, dark
energies to uplift and supersymmetry to break in a controlled fashion.
String theories where the latter is broken at the string scale can offer
different corners of the landscape to explore, with different pros and
cons. I will describe how the instabilities of these models leave room for
potentially realistic braneworld cosmologies, focusing on the simplest
known examples. (click to hide)
Wed
08.03.
14:00
HIT E41.1
Michelangelo Preti (King's College, London)
“Bootstrability in defect CFT”
abstract (click to view) We study how the exact non-perturbative integrability methods in 4D N = 4 Super-Yang-Mills can work efficiently together with the numerical conformal bootstrap techniques to go beyond the spectral observables and access previously unreachable quantities such as correlation functions at finite coupling. We consider the 1D defect CFT living on a 1/2-BPS Wilson line, whose non-perturbative spectrum is governed by the Quantum Spectral Curve (QSC). In addition, we use that the deformed setup of a cusped Wilson line is also controlled by the QSC. In terms of the defect CFT, this translates into two nontrivial relations connecting integrated 4-point correlators to cusp spectral data, such as the Bremsstrahlung and Curvature functions – known analytically from the QSC. Combining these new constraints and the spectrum of the 10 lowest-lying states with the Numerical Conformal Bootstrap, we obtain very sharp rigorous numerical bounds for the structure constants of the first non-protected states. Furthermore, we also develop analytic functional bootstrability obtaining weak coupling results for several structure constants. (click to hide)
Wed
15.03.
14:00
HIT H 42
Thomas Mertens (University of Gent)
“From JT to 3d pure gravity”
abstract (click to view) Taking inspiration from our understanding of 2d JT gravity, we develop aspects of 3d pure gravity. In particular, we propose an effective model of 3d pure gravity and discuss its factorization across entangling surfaces. Finally, we highlight some differences between gravity in its metric formulation and its first order gauge theoretic formulation, focussing on the underlying algebraic structure. Largely based on arXiv:2210.14196 and the earlier JT story in arXiv:1812.00918. (click to hide)
Wed
22.03.
14:00
HIT E41.1
Johan Henriksson (University of Pisa)
“Error-correcting codes and an ensemble of SU(2) CFTs”
abstract (click to view) Recent advances indicate that a 3d gravity partition function may be dual
not to a single CFT but to an average over an ensemble of CFTs. In my talk
I will discuss an explicit ensemble of CFTs deriving from classical binary
error-correcting codes. Such codes have been studied and classified by
discrete mathematicians for decades and give rise to chiral CFTs via a
lattice construction. By this construction, the average over the ensemble
of error-correcting codes translates to an average over CFTs with enhanced
SU(2)^c symmetry. The averaged partition function shows some gravitational
features and matches with a Poincaré sum corresponding to a sum over bulk
geometries. (click to hide)
Wed
29.03.
11:30
HIT E41.1
Lorenz Eberhardt (IAS, Princeton)
“Evaluating one-loop string amplitudes”
abstract (click to view) I will explain recent work with S. Mizera in which we give explicit evaluations of one-loop open string amplitudes at finite alpha’. Our method involves various deformations of the contour integral over the modular parameter. We directly verify that the one-loop string amplitude satisfies unitarity constraints. I will show plots of the amplitude which allows us to explore physical conjectures about their behavior, especially at high energies. (click to hide)
Wed
29.03.
14:00
HIT E41.1
Jingxiang Wu (Oxford University)
“Holomorphic Twist and Confinement”
abstract (click to view) I will describe a general procedure, known as holomorphic twist, to isolate
protected quantities in supersymmetric quantum field theories. The
result is a holomorphic, interacting quantum field theory that has infinite
dimensional symmetries. This is the natural analog of the holomorphic
sector of a 2D CFT.
I will explain how to study quantum corrections to these symmetries
and other higher operations, which together form the so-called
holomorphic factorisation algebra.
As a surprise, we find a novel UV manifestation of confinement, dubbed
as "holomorphic confinement," in the example of pure SU(N) super
Yang-Mills. (click to hide)
Thu
30.03.
12:30
HIT E41.1
Sunil Mukhi (CERN and ICTS, Bengaluru)
“Classification of Rational Conformal Field Theories With A Single Critical Exponent”
abstract (click to view) I will present the classification of all unitary,
rational conformal field theories with one non-trivial primary and central
charge c < 25 (with Brandon Rayhaun, arXiv: 2208.05486). I will also, more
briefly, review a partial classification of theories with
two nontrivial primaries, as well as some new predictions on the existence
of meromorphic CFT with c > 24. (click to hide)
Wed
05.04.
14:00
HIT E41.1 & https://ethz.zoom.us/j/3840221288
Boan Zhao (DAMTP, Cambridge)
“Higgs branch localisation on manifolds with boundary”
abstract (click to view) Supersymmetric localisation is a powerful tool to compute supersymmetric indices. The supersymmetric indices of 3d N=2 theories may be computed in two different ways: Coulomb branch localisation and Higgs branch localisation. The former scheme localizes the supersymmetric path integral to constant background magnetic fields and vanishing matter fields. The Higgs branch localisation scheme localizes the path integral to BPS vortex configurations satisfying the 2d Bogomolny equation. Such vortices are nonperturbative contributions to the index of a 3d gauge theory. Thus far, Higgs branch localisation has been performed only on closed manifolds without boundary. In this talk, I will explain how the Higgs branch localisation scheme may be generalised to three manifolds with boundary, using the hemisphere times a circle as an example. The method requires a careful consideration of supersymmetric boundary conditions for the fields in order to obtain well-behaved vortex solutions on the hemisphere. I will interpret the Higgs branch localisation calculation geometrically in terms of based quasimap moduli space from P^1 to CP^{N-1}. The talk is based on upcoming papers with Samuel Crew and Nicholas Manton. (click to hide)
Thu
20.04.
11:00
HIT E41.1
Andrea Cavaglia' (University of Torino)
“Quantum Spectral Curve for AdS3/CFT2: the proposal at work”
abstract (click to view) Recently a new integrability tool - known as Quantum Spectral Curve - was
proposed for the study of string theory on AdS3xS3xT4 with pure
Ramond-Ramond flux.
Conjecturally, these equations encode the full planar spectrum of the
theory at finite string tension, which is extremely hard to study with
direct methods.
I will review how the proposal was obtained, taking lessons from
integrability in N=4 SYM and ABJM theory and singling out, under simple
assumptions, the mathematical structure of the Quantum Spectral Curve
(QSC). Then I will present recent work on how the new equations can be
solved, which involves new challenges with respect to previous QSC
examples. Assuming the correctness of the conjecture, in this way we obtain
a rare glimpse of the non-protected spectrum of this AdS3/CFT2 duality. I
will discuss the distinctive form of these results and the many future
possibilities.
Based on arXiv: 2109.05500 and 2211.07810. (click to hide)
Wed
26.04.
14:00
HIT E41.1
Nat Levine (ENS Paris)
“Universal 1-loop divergences for integrable sigma-models”
abstract (click to view) I will show that the 1-loop divergences of integrable sigma-models take a "universal" form, under some general assumptions. "Universality" means the result depends on the choice of theory only in a coarse way: through the poles of the Lax connection in the spectral plane. We reproduce various known 1-loop beta-functions and compute some new ones. Using these universal formulae, I will show equivalence of integrable 2d sigma-models and 4d Chern-Simons theory at the level of the 1-loop RG flow.
Based on [arXiv:2209.05502] and work to appear. (click to hide)
Wed
03.05.
14:00
HIT E41.1
Dani Kaufman (University of Copenhagen)
“3d Chern-Simons Theory and Moduli of Local Systems on Surfaces”
abstract (click to view) Quantised Chern Simons theory with a compact gauge group has long been known to have connections to the representation theory of quantum groups e.g. through the construction of knot invariants. In this talk I will introduce a variation of 3d Chern-Simons with a non-compact gauge group and special boundary conditions and explain how infinite Wilson lines in this theory carry representations of non-compact quantum groups. I will also give an indication of how this story is a realisation within TQFT of the quantised moduli spaces of local systems on surfaces defined by Goncharov and Shen. Based on joint work with Nanna Aamand (University of Copenhagen). (click to hide)
Wed
10.05.
13:30
HIT E41.1
Benedikt Koenig (AEI Potsdam)
“Aspects of (gauged) 2d Supergravity”
abstract (click to view) Maximal supergravity theories in low dimensions possess exceptional symmetries. In this talk we discuss various aspects of two-dimensional maximal supergravity (2d) and its infinite dimensional exceptional symmetry group $\mathrm{E}_9$ and the compact subgroup $K(\mathrm{E}_9)$. We illustrate how to gauge subgroups of $\mathrm{E}_9$. For this, the representation theory of $K(\mathrm{E}_9)$ and the branching of $\mathrm{E}_9$ representations into $K(\mathrm{E}_9)$ representations is developed. Gauged supergravities contain a scalar potential supporting AdS solutions. Thus, in the context of holography, gauged 2d supergravity is dual to conformal quantum mechanics, for example the dWHN-BFSS matrix model. (click to hide)
Wed
17.05.
14:00
HIT E41.1
Lucía Cordova (CERN)
“O(N) monolith reloaded: sum rules and form factor bootstrap”
abstract (click to view) In this talk I will discuss the space of two-dimensional quantum field theories with a global O(N) symmetry. Previous works using S-matrix bootstrap revealed a rich space in which integrable theories appear at special points and an abundance of unknown models hinting at a non conventional UV behaviour. In order to gain more information about the unknown models, we extend the S-matrix set-up by including into the bootstrap form factors and spectral functions for operators like stress tensor and symmetry currents. I will explain how this extended set-up works and show how the associated sum rules allow us to put bounds on quantities like the central charge of the underlying conformal theories in the UV. Based on work in progress with M. Correia, A. Georgoudis and A. Vuignier. (click to hide)
Wed
24.05.
14:00
HIT E41.1
Raschid Abedin (ETH Zurich)
“Topological Lie bialgebras on power series algebras”
abstract (click to view) Lie bialgebras are algebraic structures which see applications in the theory of integrable systems and are fundamental to the theory of quantum groups. Many important infinite dimensional Lie bialgebra structures can be completed to topological Lie bialgebra structures on power series algebras. In this talk, I will give a brief introduction to Lie bialgebras and outline some classification results for these structures. In particular, I will present the recently developed classification of topological Lie bialgebra structures on the aforementioned power series algebra. (click to hide)
Wed
31.05.
14:00
HIT E41.1
Martijn Hidding (Uppsala University)
“Derivation algebra of modular iterated integrals”
abstract (click to view) Modular graph forms (MGFs), arising in the low-energy expansion of gravitational string amplitudes at genus one, are non-holomorphic modular forms expressible through specific combinations of iterated integrals of Eisenstein series. The number-theoretic properties of MGFs motivated an alternative construction of non-holomorphic modular forms from so-called equivariant iterated Eisenstein integrals by Brown. Our exploration goes beyond the depth-one case of the non-holomorphic Eisenstein series, shedding light on the relationship between the two formalisms. In this talk, I will present recent developments in our work centered around elements denoted sigma_k, which reside in a particular derivation algebra and which are pivotal to our construction of equivariant iterated integrals via generating series. I will discuss a constructive way to establish the sigma_k, which effectively predict the coefficients of the Laurent polynomials of MGFs in our construction. (click to hide)
Wed
23.08.
11:30
HIT E41.1
Ji Hoon Lee (Perimeter Institute)
“Trace relations and open string vacua”

last modified: Mon, 21 Aug 2023, 16:09 CEST

Autumn Semester 2023

Wednesday, 14:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Sibylle Driezen, Matthias Gaberdiel, Edward Mazenc

day
date
time
venue
speaker
title
Wed
27.09.
14:00
HIT E41.1
Upamanyu Moitra (ICTP)
“Finite Entanglement Entropy in String Theory”
abstract (click to view) The finiteness of the entanglement entropy in string theory has crucial implications for the information paradox, quantum gravity, and holography. In my talk, I will describe the recent progress made on establishing this finiteness. I will describe the orbifold construction appropriate for analyzing entanglement in string theory, the tachyonic divergences that one encounters and how we get a finite and calculable answer for the entanglement entropy. Time permitting, I will also discuss some additional examples where this method bears fruits. (Based on works in collaboration with Atish Dabholkar) (click to hide)
Wed
04.10.
14:00
HIT E41.1
Edward Mazenc (ETH)
“Strings from Feynman Diagrams”
abstract (click to view) To understand Holography is to understand precisely how large N gauge theories can be recast as a sum over two-dimensional worldsheets. In the simplest case, where the gauge theory reduces to a matrix integral, we can carry out this program explicitly. This talk will sketch how strings concretely emerge from gauge theory Feynman diagrams - both at the level of the worldsheet, as well as its embedding into the target space. Along the way, we will see how several open string descriptions can give rise to the same closed string background. Finally, by reinterpreting the worldsheet directly as a 2d „bulk“ spacetime, we discuss how the story of Stanford-Shenker-Saad can be upgraded away from the double-scaling limit, giving rise to new mathematical ideas such as „discrete Weil-Petersson volumes“ and exact bulk descriptions of the low-energy sector of double-scaled SYK. (Works in progress with R. Gopakumar, P. Maity, S. Komatsu, R. Kaushik & D. Sarkar) (click to hide)
Wed
11.10.
14:00
HIT E41.1
Shota Komatsu (CERN)
“Worldsheet for 2d Yang-Mills and symmetric product orbifold”
abstract (click to view) Two-dimensional Yang-Mills theory is arguably the simplest confining gauge theory and its large N expansion can be interpreted as a genus expansion of string theory. Nevertheless its worldsheet description has not been fully understood. I will propose a bosonic string dual to a chiral sector of two-dimensional Yang-Mills. The worldsheet theory consists of $\beta \gamma$-system deformed by a chiral analog of the Polchinski-Strominger term, and can be viewed as a noncritical version of nonrelativistic string theory introduced by Gomis and Ooguri. I will then comment on extensions of our worldsheet theory which are candidate duals of symmetric product orbifolds of arbitrary seed CFTs and their $T\bar{T}$ deformation. (click to hide)
Wed
18.10.
14:00
HIT E41.1
Frank Coronado (ETH)
“Correlator/amplitude duality and ten-dimensional symmetry.”
abstract (click to view) In planar N=4 SYM, correlation functions of the stress tensor are dual to massless scattering amplitudes when the operators form a light-like polygon. I will present a (conjectured) generalization of this duality which equates correlators of determinant operators, in a special ten-dimensional null limit, with massive scattering amplitudes in the Coulomb branch of N=4. By using a novel twistor space representation for the determinant operators and matrix duality we compute the planar loop-integrands of these correlators. We show these planar integrands contain only ten-dimensional distances which combine the spacetime and R-charge space distances. This is amenable to the null limit that corresponds to the amplitude. (click to hide)
Wed
25.10.
14:00
HIT E41.1
Martijn Hidding (ETH)
“Special Functions in String Amplitudes and Feynman Integrals”
abstract (click to view) In this talk, I'll cover various aspects of my research exploring the role of special functions in string amplitudes and quantum field theory. First, I'll review the appearance of multiple polylogarithms and elliptic multiple polylogarithms in (open-)string amplitudes of genus 0 and 1 and Feynman integrals relevant to massive QCD. The next part of the talk will focus on elliptic modular graph forms, based on the treatment in arXiv:2208.11116, which show up in closed-string amplitudes at genus-one. I'll explain how these functions can be expressed in terms of iterated integrals, and discuss their modular covariance properties. Next, I will introduce the function space of equivariant iterated Eisenstein integrals, which we studied in arXiv:2209.06772, and will examine what combinations of iterated integrals are modular covariant. I'll conclude by briefly mentioning work on new polylogarithmic functions on Riemann surfaces of arbitrary genus (arXiv:2306.08644) and its role in amplitude computations. (click to hide)
Wed
01.11.
14:00
HIT E41.1
Priyadarshi Paul (ICTS)
“The Hilbert space & holography of information in de Sitter quantum gravity”
abstract (click to view) We obtain solutions of the Wheeler-DeWitt equation with positive cosmological constant for a closed universe in the large-volume limit. We argue that this space of solutions provides a complete basis for the Hilbert space of quantum gravity in an asymptotically de Sitter spacetime. Our solutions take the form of a universal phase factor multiplied by distinct diffeomorphism invariant functionals, with simple Weyl transformation properties, that obey the same Ward identities as a CFT partition function. Each functional can be thought of as specifying a “theory” and, in this sense, the space of solutions is like “theory space”.
We propose that the norm on this space of solutions is obtained by integrating the squared wavefunctional over field configurations and dividing by the volume of the diff-and-Weyl group. We apply our formalism to cosmological correlators and propose that they should be understood as gauge-fixed observables. In a theory of quantum gravity, we demonstrate a version of the principle of holography of information: cosmological correlators in an arbitrarily small region suffice to completely specify the state. (click to hide)
Wed
08.11.
14:00
HIT E41.1
Anthony Ashmore (Sorbonne)
“Machine learning for geometry and string compactifications”
abstract (click to view) Understanding Calabi-Yau metrics and hermitian Yang-Mills connections has long been a challenge in mathematics and theoretical physics. These geometric objects play a crucial role in constructing realistic models of particle physics in string theory. However, with no closed-form expressions for them, we are unable to compute basic quantities in top-down string models, such as particle masses and couplings.
Breakthroughs in machine learning have opened a new path to tackle this problem. After recalling the relationship between these geometric ingredients and 4d effective field theory, I will review recent progress in using machine learning to calculate these metrics and connections numerically. Finally, I will highlight how this newly available geometric data can be used, including studying the spectrum of Laplace-type operators on a Calabi-Yau in the presence of a background gauge field. (click to hide)
Wed
15.11.
14:00
HIT E41.1
Tim Meier (Humboldt U. Berlin)
“Twist noncommutative gauge theories”
abstract (click to view) Applying the Yang-Baxter (YB) deformations to the famously integrable AdS5 x S5 string give rise to a variety of new integrable models. In the context of the AdS/CFT correspondence, these models are conjectured to be dual to gauge theories on various noncommutative spacetimes obtained via Drinfel’d twists. To date, however, it was unclear how to formulate such noncommutative gauge theories precisely beyond the simplest case of constant noncommutativity. In my talk, I will show how to construct gauge invariant noncommutative Yang-Mills actions for a broad class of noncommutative structures, relying on a deformed version of the Hodge star operation. I will also show how to include matter fields and hence how to construct noncommutative versions of N=4 SYM which give promising candidates for the dual theory to YB deformations of the AdS5 x S5 string. I will construct gauge invariant operators for the deformed models. Finally, I will comment on the connection to a possible spin chain picture for the one loop anomalous dimension of such operators. (click to hide)
Wed
22.11.
11:30
HIT E41.1
Erez Urbach (Weizmann Institute)
“The Black Hole/String Transition in Anti-de Sitter Space”
abstract (click to view) String stars, or Horowitz-Polchinski solutions, are string theory saddles with normalizable condensates of thermal-winding strings. In the past, string stars were offered as a possible description of stringy (Euclidean) black holes in asymptotically flat spacetime, close to the Hagedorn temperature. I will discuss the thermodynamic properties of string stars in asymptotically (thermal) anti-de Sitter background (including AdS3 with NS-NS flux), their possible connection to small black holes in AdS, and their implications for holography. I will also present new ``winding-string gas'' saddles for confining holographic backgrounds such as the Witten model, and their relation to the deconfined phase of 3+1 pure Yang-Mills. (click to hide)
Wed
22.11.
14:00
HIT E41.1
Fiona Seibold (Imperial College London)
“S-matrix on effective strings and compactified membranes.”
abstract (click to view) The low-energy dynamics of confining strings is captured by the Nambu-Goto area action, which in critical dimension is related to an integrable TTbar deformation of a free theory. In this talk I will consider the setup of a membrane compactified on a circle, leading to a tower of massive modes. I will present the perturbative worldsheet S-matrix, compare with the Nambu-Goto case, and discuss the integrability of the model. (click to hide)
Wed
06.12.
11:30
HIT E41.1
Anthony Houppe (ETH)
“Microstate geometries without supersymmetry”
abstract (click to view) Using supersymmetry, large families of microstate geometries have been constructed in AdS3. The holographic dictionary of these solutions is now well established, and has been extensively used to compute vevs and correlators of the states of the D1-D5 CFT directly from the bulk, with a remarkable matching with the CFT values. The situation is however very different away from the BPS regime: few bulk geometries are known, and the matching is complicated by the absence of protected operators. In this talk, I will present recent advances on the construction of non-supersymmetric microstate geometries in AdS3, and on the identification of their CFT dual. (click to hide)
Wed
06.12.
14:00
HIT E41.1
Paul Balduf (University of Waterloo)
“Statistics of Feynman periods in phi^4-theory.”
abstract (click to view) The Feynman period is the contribution of a subdivergence-free log-divergent graph to the beta function, or equivalently the simple pole of its amplitude in dimensional regularization. We have used an algorithm recently developed by Borinsky to compute numerical approximations to the periods of 1.3 million distinct graphs in phi^4 theory, including all subdivergence-free graphs up to and including 13 loops. On the one hand, we obtain an accurate numerical value for the primitive beta function of phi^4 theory at 13 loops. On the other hand, and more importantly, this large data set allows us to accurately determine distribution parameters, growth rates, and correlations between the period and numerous graph-theoretic properties.
In my talk, I will show some of these numerical and qualitative results. A special focus will be the distribution of periods, the presence of exotic "outlier" amplitudes, and the implications of these results for non-complete samples of Feynman graphs at large loop order. (click to hide)

last modified: Tue, 28 Nov 2023, 15:17 CET

Spring Semester 2024

Wednesday, 14:00, HIT E41.1

Organised by: Niklas Beisert, Johannes Broedel, Sibylle Driezen, Matthias Gaberdiel, Edward Mazenc

day
date
time
venue
speaker
title
Wed
28.02.
14:00
HIT E41.1
Vladimir Kazakov (ENS Paris)
“Principal chiral model in arbitrary magnetic field: exact solution in planar limit”
abstract (click to view) The two-dimensional Principal Chiral Model (PCM) has been considered since long as an instructive example of a QFT bearing certain similarities with QCD: asymptotic freedom, dimensional transmutation with a physical mass spectrum and a non-trivial 't Hooft's large N limit. In addition, it is an integrable QFT, with the known physical S-matrix. In our 1994 paper with V.Fateev and P.Wiegmann, we found not only the exact but also explicit solution of the vacuum energy of SU(N)xSU(N) PCM in the 't Hooft limit in the presence of specific, albeit arbitrary strong, "magnetic" field (the chemical potential of density of physical particles). The shape of this field repeated the Perron-Frobenius (PF) mode on the su(N) Dynkin diagram. I will present our recent work with E.Sobko and K.Zarembo (arxiv:2312.04801) where we explicitly solved the Bethe equation for the magnetic field of arbitrary shape. We also studied this solution in the case of small deviations of the magnetic field from the PF mode and found a perfect correspondence with the known perturbative and strong coupling results. I will also mention our results of 1/N expansion of the energy and a possible interpretation of PCF as a 2+1-dimensional noncritical string theory, where the role of the 3rd dimension is played by Dynkin diagram. (click to hide)
Wed
06.03.
14:00
HIT E41.1
Petr Kravchuk (King’s College London)
“AdS three-body problem at large spin”
abstract (click to view) Motivated by the problem of understanding multi-twist operators in general CFTs, I will discuss the interacting spectrum of large-spin three-particle states in AdS. In particular, I will explain that thanks to the AdS curvature this particular limit of the three-body problem is tractable. The large spin limit effectively becomes a semiclassical limit of a Berezin-Toeplitz Hamiltonian, which allows us to analyze the leading-twist spectrum analytically. Work in progress with Jeremy Mann. (click to hide)
Thu
07.03.
12:30
HIT E41.1
Fedor Popov (New York University)
“Holography on the Quantum Disk”
abstract (click to view) Motivated by recent study of DSSYK and the non-commutative nature of its bulk dual, I will review and analyze an example of a non-commutative spacetime known as the quantum disk proposed by L. Vaksman. The quantum disk is defined as the space whose isometries are generated by the quantum algebra U_q(su_{1,1}). I will review how this algebra is defined and its associated group SL_q(2) that it generates, highlighting its non-trivial coproduct that sources bulk non-commutativity. After that I will analyze the structure of holography on the quantum disk and study the imprint of non-commutativity on the putative boundary dual. (click to hide)
Wed
13.03.
14:00
HIT E41.1
Michele Galli (Humboldt U. Berlin)
“Consistent truncations and KK spectra via exceptional field theory”
abstract (click to view) 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. (click to hide)
Wed
20.03.
14:00
HIT E41.1
Victor Gorbenko (EPFL Lausanne)
“Quantum groups as global symmetries”
abstract (click to view) We would like to answer the following question: can a global internal symmetry of a quantum filed theory be a quantum group, and if yes, what are the the consequences of such symmetry? We discuss a concrete example where this situation is realized in a non-local and non-unitary 2D CFT. This allows us to derive constraints that are similar to the case of usual symmetries and that should be satisfied by a quantum-group-symmetric theory generically. (click to hide)
Wed
27.03.
14:00
HIT E41.1
Yoann Sohnle Moreno (Uppsala University)
“Solving a Feynman integral depending on two elliptic curves: the 5 mass Kite family”
abstract (click to view) We consider the 5-mass kite family of self-energy Feynman integrals and present a systematic approach for putting its associated differential equation into a convenient form (also called the epsilon or canonical form).
We show that this is most easily achieved by making a change of variables from the kinematic space to the function space of two tori with punctures.
We demonstrate how the locations of relevant punctures on these tori, which are required to parametrize the full image of the kinematic space onto this moduli space, can be extracted from integrals over the solution of homogeneous differential equations (also called maximal cuts).
A boundary value is provided to systematically solve the differential equation in terms of iterated integrals over so-called Kronecker-Eisenstein coefficients -- the equivalents of rational functions on a torus. (click to hide)
Wed
17.04.
14:00
HIT E41.1
Saskia Demulder (Ben Gurion U.)
“R-defects: topological defects in non-Abelian Chern-Simons”
abstract (click to view) Topological defects defy our conventional understanding of what symmetries are. Known topological defects are however mostly confined to discrete or Abelian continuous and compact groups. We construct a new class of topological defects in the Chern Simons theory with non-Abelian, non-compact gauge groups. This new class of defects are characterised by a solution of the so-called modified-classical Yang-Baxter equation and are thus linked to Lagrangian subalgebras. This algebraic description enables us to tackle their fusion algebra both using a Lagrangian path integral and an Hamiltonian perspective. If time permits we will discuss possible applications to 3d gravity and its higher spin generalisation.
This is work in progress with A.S. Arvanitakis, L.T. Cole, and D.C. Thompson. (click to hide)
Wed
24.04.
14:00
HIT E41.1
Nejc Ceplak (Trinity College Dublin)
“Black Hole Singularity from OPE”
abstract (click to view) Eternal asymptotically AdS black holes are dual to thermofield double states on the boundary CFT. It has long been known that black hole singularities have certain signatures in boundary thermal two-point functions via the so-called bouncing geodesics. However, the understanding of these signatures from the CFT point of view has been elusive. In this talk I will try present some progress in answering this question.
I will analyse the boundary CFT correlation function of scalar operators and decompose them using the Operator Product Expansion (OPE). I will show that the stress-tensor sector of the correlator develops singularities precisely at the points that are connected by bulk bouncing geodesics. This means that black hole singularities are encoded in the analytic behavior of the boundary correlators determined by multiple stress tensor exchanges.
Furthermore, I will show that in the limit where the conformal dimension of the operators is large, the stress-tensor contribution develops a branch point singularity as predicted by the geodesic analysis. I will also argue that the appearance of complexified geodesics, which play an important role in computing the full correlator, is related to the contributions
of the double-trace operators in the boundary CFT. (click to hide)
Thu
02.05.
12:30
HIT E41.1
Jnan Maharana (Bhubaneswar, NISER)
“Production of KK states in large radius compactification scenario”
abstract (click to view) We consider production of Kaluza-Klein states at LHC in the Large Radius
Compactification scenario. In thi proposal the compactification scale
could be in the TeV range. Therefore, some of the predictions can be
subject to experimental tests at LHC. Thousands of models have been proposed following the papers of ADD and AADD. We derive boulds on (a)
total cross sections for production of KK states and (b) differential cross section for this inelastic reaction from general principles of local field theories. The results have minimal model dependent. There are intricate problems in study of inelastic unequal mass scatterings. Attentions will be paid to overcome the associated problems. (click to hide)
Wed
08.05.
14:00
HIT E41.1
Enrico Pajer (U. of Cambridge)
t.b.a.
Wed
15.05.
14:00
HIT E41.1
Alexander Tumanov (LPENS Paris)
t.b.a.
Wed
22.05.
14:00
HIT E41.1
Carlos Mafra (Southampton U.)
t.b.a.

last modified: Wed, 24 Apr 2024, 18:54 CEST