# GCS postdocs and students colloquium

Meeting monthly

An occasion to discuss and share insights for students and postdocs

https://sites.google.com/perimeterinstitute.ca/gcs-colloquium/home

# On the 6d Origin of Non-invertible Symmetries in 4d

Bashmakov, Del Zotto, Hasan, https://arxiv.org/abs/2206.07073

# Global structures from the IR

Del Zotto, García Etxebarria, https://arxiv.org/abs/2204.06495

# Annual Meeting

Simons Foundation, November 17-18, 2022

Ingrid Daubechies Auditorium

162 Fifth Avenue, Flatiron Institute

New York, NY

Thurs.: 8:30 AM—5 PM

Fri.: 8:30 AM—2 PM

# Modular tensor categories, subcategories, and Galois orbits

Plavnik, Schopieray, Yu, Zhang, https://arxiv.org/abs/2111.05228

# GCS2022 School

The GCS2022 School is the second week of the program *Global Categorical Symmetries 2022*, held at the Perimeter Institute for Theoretical Physics June 6-17. Videos are available at https://pirsa.org/C22008.

## Minicourses

- Clay Córdova:
*Introduction to anomalies in quantum field theory* - Dan Freed:
*Finite symmetry in QFT* - Mike Hopkins:
*Lattice systems and topological field theories* - Kantaro Ohmori:
*Introduction to symmetries in quantum field theory*

Problem sessions will be TAed by Arun Debray and Ho Tat Lam.

## Suggested readings

- Córdova, Freed, Lam, and Seiberg, Anomalies in the Space of Couplings I.
- Córdova and Ohmori, Anomaly Obstructions to Symmetry preserving Gapped Phases.
- Freed, The cobordism hypothesis.
- Gaiotto, Kapustin, Seiberg, and Willett, Generalized Global Symmetries.
- Lurie, On the classification of topological field theories.
- Teleman, Five lectures on topological field theory. Errata.
- Thorngren and Wang, Fusion Category Symmetry I.

## Lecture notes

- Notes by Dan Freed: https://web.ma.utexas.edu/users/dafr/Freed_perim.pdf
- Notes by Arun Debray: https://www.math.purdue.edu/~adebray/lecture_notes/gcs2022_notes.pdf
- Notes by Davi Costa: https://www.overleaf.com/read/cdspwyfhszsh

## Problem sets

- Dan Freed: Homework 1. Homework 2. Homework 3.
- Clay Cordova: Homework.
- Kantaro Ohmori: Homework.
- Mike Hopkins: Homework.

## Detailed Schedule

#### Monday, June 13

9:30-10:30: Ohmori, *Introduction to symmetries in quantum field theory*

11:30-12:30: Freed, *Finite symmetries in QFT*

14:00-15:00: Cordova, *Introduction to anomalies in quantum field theory*

16:00-17:00: Hopkins, *Lattice systems and topological field theories*

#### Tuesday, June 14

9:00-10:00: Freed, *Finite symmetries in QFT*

11:00-12:00: Ohmori, *Introduction to symmetries in quantum field theory*

13:30-14:30: Cordova, *Introduction to anomalies in quantum field theory*

15:00-17:00: *Problem session / open discussion*

17:00-19:00: BBQ

#### Wednesday, June 15

9:00-10:00: Hopkins, *Lattice systems and topological field theories*

11:00-12:00: Freed, *Finite symmetries in QFT*

13:30-14:30: Ohmori, *Introduction to symmetries in quantum field theory*

15:00-17:00: *Problem session / open discussion*

#### Thursday, June 16

9:00-10:00: Cordova, *Introduction to anomalies in quantum field theory*

11:00-12:00: Ohmori, *Introduction to symmetries in quantum field theory*

13:30-14:30: Hopkins, *Lattice systems and topological field theories*

15:00-17:00: *Problem session / open discussion*

#### Friday, June 17

9:00-10:00: Freed, *Finite symmetries in QFT*

11:00-12:00: Hopkins, *Lattice systems and topological field theories*

13:30-14:30: Cordova, *Introduction to anomalies in quantum field theory*

15:00-17:00: *Problem session / open discussion / goodbye*

# GCS2022 conference schedule and abstracts

This is the schedule for the first week of the GCS2022 conference and school. Videos are available at https://pirsa.org/C22008.

## Schedule

(All times are in Eastern Daylight Time}

### Monday, June 6

9:30-9:45: *Welcome and opening remarks*

9:45-10:45: Justin Kaidi — *Non-Invertible Symmetries in d>2*

10:45-11:45: *Coffee break*

11:45-12:45: Andrei Okounkov — *Monodromy and derived equivalences*

12:45-14:00: *Lunch*

14:00-15:00: Emily Nardoni — *Lessons from SU(N) Seiberg-Witten Geometry*

15:00-15:45: *Coffee break*

15:45-16:45: Kevin Costello — *Vertex algebras and self-dual Yang-Mills theory*

### Tuesday, June 7

9:00-10:00: Shu-Heng Shao — *Non-invertible Global Symmetries in the Standard Model*

10:00-10:45: *Coffee break*

10:45-11:45: Pavel Etingof — *Analytic Langlands correspondence over C and R*

11:45-12:00: *Short break*

12:00-13:00: Colleen Delaney — *Hopf algebras play an analogous role in some topological and non-topological QFTs*

13:00-14:45: *Lunch*

14:45-17:00: Gong show

17:00-18:00: *Reception*

### Wednesday, June 8

9:00-10:00: Cris Negron — *A (kind of) monoidal localization theorem for the small quantum group*

10:00-11:00: *Coffee break*

11:00-12:00: Iñaki García-Etxebarria — *Symmetries from string theory*

12:00-14:00: *Lunch*

14:00-15:00: Nathan Seiberg (Colloquium) — *Quantum Field Theory, Separation of Scales, and Beyond*

15:00-16:00: *Coffee break*

### Thursday, June 9

9:00-10:00: André Henriques — *All unitary 2D QFTs share the same state space*

10:00-10:45: *Coffee break*

10:45-11:45: Mina Aganagic — *Knot categorification from homological mirror symmetry*

11:45-12:00: *Short break*

12:00-13:00 David Reutter — *Higher S-matrices and higher modular categories*

13:00-14:45: *Lunch*

14:45-15:45: Federico Bonetti — *’t Hooft anomalies of QFTs realized in string theory*

15:45-16:30: *Coffee break*

### Friday, June 10

9:00-10:00: Sakura Schäfer-Nameki — *Non-Invertible Higher-Categorical Symmetries*

10:00-10:45: *Coffee break*

10:45-11:45: Thomas Dumitrescu — *Line Defect Quantum Numbers and Anomalies*

11:45-12:00: *Short break*

12:00-13:00: Tudor Dimofte — *TQFT’s and flat connections*

13-14:45: *Lunch*

14:45-16:00: Posters and goodbyes

## Abstracts

### Aganagic: *Knot categorification from homological mirror symmetry*

Khovanov showed in ‘99 that the Jones polynomial arises as the Euler characteristic of a homology theory. The knot categorification problem is to find a general construction of knot homology groups and to explain their meaning: what are they homologies of?

Homological mirror symmetry, formulated by Kontsevich in ’94, naturally produces hosts of homological invariants. Sometimes, it can be made manifest, and then its striking mathematical power comes to fore. Typically though, it leads to invariants which have no particular interest outside of the problem at hand.

I will explain that there is a vast new family of mirror pairs of manifolds for which homological mirror symmetry does lead to interesting invariants, and solves the knot categorification problem.

### Federico Bonetti: *’t Hooft anomalies of QFTs realized in string theory*

String theory constructions allow one to realize vast classes of non-trivial quantum field theories (QFTs), including many strongly coupled models that elude a conventional Lagrangian description. ’t Hooft anomalies for global symmetries are robust observables that are particularly well-suited to explore QFTs realized in string theory. In this talk, I will discuss systematic methods to compute anomalies of theories engineered with branes, using as input the geometry and flux configuration transverse to the non-compact directions of the branes worldvolume. Examples from M-theory and Type IIB string theory illustrate the versatility of this approach, which can capture both ordinary and generalized symmetries, continuous or discrete.

### Costello: *Vertex algebras and self-dual Yang-Mills theory*

I’ll discuss a vertex algebra whose correlators are scattering amplitudes (and form factors) of self-dual Yang-Mills theory, for certain gauge groups and matter. The vertex algebra is a kind of vertex quantum group, and is a cousin of the affine Yangian. This is joint work with Natalie Paquette.

### Delaney: *Hopf algebras play an analogous role in some topological and non-topological QFTs*

A frequent theme in mathematical approaches to quantum field theory is being able to draw intuitive but rigorous pictures of particle interactions. For example, in theories like QED and QCD, Feynman diagrams can be organized into a Hopf algebra structure in such a way that models renormalization of Feynman integrals. One can draw an analogy with the role of Hopf algebras in (2+1)D topological quantum field theory, where in this second setting one can think of certain string diagrams as Feynman diagrams whose Witten-Reshetikhin-Turaev amplitudes are encoded by the representation theory of some (weak) Hopf algebra. This talk is intended to (1) be accessible to both mathematicians and physicians, (2) invite a dialogue about the meaningfulness of this analogy and (3) serve as an aperitif to the later talks.

### Dimofte: *TQFT’s and flat connections*

I will discuss some of the (higher) structure of TQFT’s that can be deformed by flat connections for continuous global symmetries, focusing on examples coming from twists of 3d supersymmetric theories, and the manifestation of this structure in boundary VOA’s.

### Dumitrescu: *Line Defect Quantum Numbers and Anomalies*

I will consider four-dimensional gauge theories whose global symmetries admit certain discrete ’t Hooft anomalies that are intimately related to the (fractionalized) global-symmetry quantum numbers of Wilson-’t Hooft line defects in the theory. Determining these quantum numbers is typically straightforward for Wilson lines, but requires a careful analysis of fermion zero modes for ’t Hooft lines, which I will describe for several classes of examples. This in turn leads to a calculation of the anomaly. Along the way I will comment on how this understanding relates to some classic and recent examples in the literature.

### Etingof: *Analytic Langlands correspondence over ***C** and **R**

**C**and

**R**

I will review the analytic component of the geometric Langlands correspondence, developed recently in my joint work with E. Frenkel and D. Kazhdan (based on previous works by other authors, including A. Braverman, R. Langlands, J. Teschner, M. Kontsevich), with a special focus on archimedian local fields, especially R. This is based on our work with E. Frenkel and D. Kazhdan and insights shared by D. Gaiotto and E. Witten.

### García-Etxebaria: *Symmetries from string theory*

It is possible to construct interesting field theories by placing string theory on suitable singular geometries, and adding branes. In the fairly special cases where Lagrangians are known for the resulting theories, field theory arguments often show that these theories have generalised symmetry structures. In this talk I will review recent work developing a dictionary, valid even in the absence of a known Lagrangian description, between properties of the string theory geometry and generalised symmetries of the associated field theories.

### Henriques: *All unitary 2D QFTs share the same state space*

A unitary 1d QFT consists of a Hilbert space and a Hamiltonian. A group acting on a 1d QFT is a group acting on the Hilbert space, commuting with the Hamiltonian. Note that the *data* of an action only involves the Hilbert space. The Hamiltonian is only there to provide a constraint. Moreover, all 1d QFT have isomorphic Hilbert spaces (except in special cases, e.g. in the case of a 1d TQFT, when the Hilbert space is finite dimensional).

A unitary 2d QFT consists of the 0-dimensional and 1-dimensional part of the QFT, along with the data of the Stress-energy tensor. An action of a fusion category on a 2d QFT is again something where the *data* only involves the 0-dimensional and 1-dimensional part of the QFT, while the Stress-energy tensor is only there to provide a constraint. The upshot is that it makes sense to act on the 0-dimensional and 1-dimensional part of the QFT. Moreover, I conjecture that all 2d QFTs have isomorphic 0-dimensional + 1-dimensional parts (except in special cases, e.g. in the case of a chiral CFT).

### Kaidi: *Non-Invertible Symmetries in d>2*

In this talk I will review some recent progress in the study of non-invertible symmetries in dimensions d>2. After introducing known constructions and describing how they lead to constraints on RG flows, I will discuss how non-invertible symmetries can also be used to obtain *new* RG flows. This involves the notion of “non-invertible twisted compactification,” which can be used to construct e.g. novel 3d N=6 theories from 4d N=4 SYM. Finally, I will describe upcoming work in which we give a partial criterion for determining whether a given non-invertible symmetry is “intrinsically non-invertible”, or whether it can be recast (in an appropriate sense) as a standard invertible symmetry with an anomaly.

### Okounkov: *Monodromy and derived equivalences*

This will be an introductory discussion of our joint work with Roman Bezrukavnikov. Given a symplectic resolution X, one may study its Gromov-Witten theory and the monodromy group of the curve-counting functions in the Kähler variables. There is also a large group of derived autoequivalences of X coming from its quantization in large prime characteristic, as studied by Bezrukavnikov and collaborators. Conjecturally, the action of the latter group on K(X) is identified with the former group, and we prove this for many X.

### Nardoni: *Lessons from SU(N) Seiberg-Witten Geometry*

Motivated by applications to soft supersymmetry breaking, we revisit the Seiberg-Witten solution for N=2 super Yang-Mills theory in four dimensions with gauge group SU(N). We present a simple exact Taylor series expansion for the periods obtained at the origin of moduli space, thereby generalizing earlier results for SU(2) and SU(3). With the help of these analytic results and others, we analyze the global structure of the Kahler potential, presenting evidence for a conjecture that the unique global minimum is the curve at the origin of moduli space.

Two applications of these results are considered. Firstly, we analyze candidate walls of marginal stability of BPS states on special slices for which the expansions of the periods simplify. Secondly, we consider soft supersymmetry breaking of the N=2 theory to non-supersymmetric four-dimensional SU(N) gauge theory with two massless adjoint Weyl fermions (“adjoint QCD”). The Seiberg-Witten Kahler potential and strong coupling spectrum play a crucial role in this analysis, which ultimately leads to an exploration of the adjoint QCD phase diagram.

### Negron: *A (kind of) monoidal localization theorem for the small quantum group*

I will talk about a monoidal localization theorem for the small quantum group u_q(G), where G is a reductive algebraic group and q is a root of unity. In joint work with Julia Pevtsova, we show that the category of representations for u_q(G) admits a fully faithful tensor embedding into the category of coherent sheaves over a “quantum” flag variety. This quantum flag variety is, essentially, some finitely fibered space over the classical flag variety G/B. I will explain how this embedding theorem codifies certain relationships between the small quantum group and its quantum Borels.

### Reutter: *Higher S-matrices and higher modular categories*

Every braided fusion category has a `framed S-matrix pairing’ which records the braiding between simple objects. Non-degeneracy/Morita invertibility of the category (aka `modularity’ in the oriented case) is equivalent to non-degeneracy of this pairing. I will define higher-dimensional versions of S-matrices which pair morphisms of complementary dimension in higher semisimple categories and sketch a proof that these pairings are non-degenerate if and only if the higher category is. Along the way, I will introduce higher semisimple categories and higher fusion categories and interpret these results in terms of the associated anomalous topological quantum field theories. This is based on joint work in progress with Theo Johnson-Freyd.

### Schafer-Nameki: *Non-Invertible Higher-Categorical Symmetries*

I will discuss a proposal for generating non-invertible symmetries in QFTs in d>2, by gauging outer automorphisms. First this will be illustrated in 3d, where the framework is relatively well established, and then extended to higher dimensions. For 4d gauge theories, a comparison to other approaches to non-invertible symmetries is provided, in particular the map to gauging theories with mixed anomalies. This talk is based on work that appeared in 2204.06564 and in progress, with Lakshya Bharwaj (Oxford), Lea Bottini (Oxford) and Apoov Tiwari (Stockholm).

### Seiberg: *Quantum Field Theory, Separation of Scales, and Beyond*

We will review the role of Quantum Field Theory (QFT) in modern physics. We will highlight how QFT uses a reductionist perspective as a powerful quantitative tool relating phenomena at different length and energy scales. We will then discuss various examples motivated by string theory and lattice models that challenge this separation of scales and seem outside the standard framework of QFT. These lattice models include theories of fractons and other exotic systems.

### Shao: *Non-invertible Global Symmetries in the Standard Model*

We identify infinitely many non-invertible generalized global symmetries in QED and QCD for the real world in the massless limit. In QED, while there is no conserved Noether current for the axial symmetry because of the ABJ anomaly, for every rational angle, we construct a conserved and gauge-invariant topological symmetry operator. Intuitively, it is a composition of the axial rotation and a fractional quantum Hall state coupled to the electromagnetic U(1) gauge field. These conserved symmetry operators do not obey a group multiplication law, but a non-invertible fusion algebra over TQFT coefficients. These non-invertible symmetries lead to selection rules, which are consistent with the scattering amplitudes in QED. We further generalize our construction to QCD, and show that the neutral pion decay can be understood from a matching condition of the non-invertible global symmetry.

# Non-Invertible Chiral Symmetry and Exponential Hierarchies

Córdova, Ohmori, https://arxiv.org/abs/2205.06243

# Non-invertible Condensation, Duality, and Triality Defects in 3+1 Dimensions

Choi, Córdova, Hsin, Lam, Shao, https://arxiv.org/abs/2204.09025

# GCS2022 Conference and School

**Perimeter Institute for Theoretical Physics**, 6-17 June 2022

The conference and school will be “hybrid” style: most speakers will be in-person, with some virtual speakers; about half of the participants will be in-person, and talks will also be live-streamed on Zoom. Videos will be archived on pirsa.org. Further details can be found at Perimeter’s conference website. Registration has now closed.

Immediately following GCS2022 will be the school and conference QFT for Mathematicians. Although the two events are logically separate, with different organizing teams and registrations, we purposefully scheduled the two schools to be back-to-back so that students can attend both.

## Program

### 6-10 June 2022: Research Conference

**Speakers:** Mina Aganagic, Federico Bonetti, Kevin Costello, Colleen Delaney, Tudor Dimofte, Thomas Dumitrescu, Pavel Etingof, Iñaki García Etxebarria, André Henriques, Justin Kaidi, Emily Nardoni, Cris Negron, Andrei Okounkov, David Reutter, Sakura Schäfer-Nameki, Nathan Seiberg, Shu-Heng Shao

Conference schedule, titles, and abstracts

### 13-17 June 2022: School

**Lecturers:** Clay Córdova, Dan Freed, Mike Hopkins, Kantaro Ohmori

**TAs:** Arun Debray, Ho Tat Lam

# Generalized Global Symmetries, Quantum Field Theory, and Geometry

Simons Center for Geometry and Physics, 19-23 September 2022

Satellite event of the collaboration organised thanks to the support of the SCGP.

# Long-range entanglement from measuring symmetry-protected topological phases

Tantivasadakarn, Thorngren, Vishwanath, Verresen, https://arxiv.org/abs/2112.01519

# 2-Group Symmetries and M-theory

Del Zotto, García Etxebarria, Schäfer-Nameki, https://arxiv.org/abs/2203.10097

# Corner Structure of Four-Dimensional General Relativity in the Coframe Formalism

Canepa, Cattaneo, https://arxiv.org/abs/2202.08684

# Generalized Symmetry Breaking Scales and Weak Gravity Conjectures

Córdova, Ohmori, Rudelius, https://arxiv.org/abs/2202.05866

# Higher Symmetries of 5d Orbifold SCFTs

Del Zotto, Heckman, Meynet, Moscrop, Zhang, https://arxiv.org/abs/2201.08372

# Thorngren Scandinavian Lectures

**Uppsala University** ~~May 27-June 3, 2022~~ (POSTPONED)

The precise program will be announced on this page closer to the date. It is possible to follow these lectures from zoom. Please, contact the organizer to be added to the mailing list.

Lecture 1 – ~~May 27, 2022~~

Lecture 2 – ~~May 30, 2022~~

Lecture 3 – ~~June 1st, 2022~~

Lecture 4 – ~~June 3rd, 2022~~

Organizer: Michele Del Zotto

# The Geometry of Decoupling Fields

Bah, Bonetti, Leung, Weck, https://arxiv.org/abs/2112.07796

# Symmetry TFTs from String Theory

Apruzzi, Bonetti, García Etxebarria, Hosseini, Schäfer-Nameki, https://arxiv.org/abs/2112.02092

# M5-branes Probing Flux Backgrounds

Bah, Bonetti, Leung, Weck, https://arxiv.org/abs/2111.01790

# Anomaly Matching Across Dimensions and Supersymmetric Cardy Formulae

Ohmori, Tizzano, https://arxiv.org/abs/2112.13445

# San Diego Focus Meeting

January 10-14, 2022

Meeting for members of the collaboration only.

PARTICIPANTS

Ibrahima Bah (JHU)

Alberto Cattaneo (University of Zurich)

Clay Córdova (University of Chicago)

Michele Del Zotto (Uppsala University)

Thomas Dumitrescu (UCLA)

Dan Freed (University of Texas, Austin)

Iñaki García Etxebarria (Durham University)

Michael Hopkins (Harvard)

Ken Intriligator (UCSD)

Theo Johnson-Freyd (Dalhousie University and PI)

David Jordan (University of Edinburgh)

Nytia Kitchloo (JHU)

Julia Plavnik (Indiana University)

Ryan Thorngren (KITP)

SCHEDULE

Mornings 9-12 and Afternoons 14-16: structured talks/discussions. All the other times: free discussions/collaboration. The precise agenda for each day is decided by the participants on the day prior.

**Local organizer:** Ken Intriligator

# Kramers-Wannier-like duality defects in (3 + 1)d gauge theories

Kaidi, Ohmori, Zheng, https://arxiv.org/abs/2111.01141

# Non-Invertible Duality Defects in 3+1 Dimensions

Choi, Cordova, Hsin, Lam, Shao, https://arxiv.org/abs/2111.01139

# We Are Hiring!

# Zesting produces modular isotopes and explains their topological invariants

Delaney, Kim, Plavnik. https://arxiv.org/abs/2107.11374

# Claudia Scheimbauer on “Dualizabitility, higher categories, and topological field theories”

Claudia has given a series of seven lectures at the Copenhagen Center for Geometry and Topology.

**Dualizabitility, higher categories, and topological field theories**

In the past decade, using higher categories has proven to be an essential ingredient in the study of topological field theories (TFTs) from a mathematical perspective. The most prominent and seminal result is the Cobordism Hypothesis, which gives a beautiful classification of “fully extended” topological field theories. Here, fully extended means that our TFT can be evaluated at manifolds and bordisms of all dimensions below a given one; conversely, the mathematical language needed to describe the structure is that of higher categories and dualizability therein. In physics, we can interpret these values at all dimensions as (possibly higher) categories of boundary conditions, as point insertions/observables, line operators or higher dimensional operators, etc., depending on the stiuation.

The main goal of this master class will be to explain how to use the cobordism hypothesis to construct TFTs and variations thereof. One example we will look at in detail arises from factorization homology for E_n-algebras, which will also be a key tool in the parallel master class. We will discuss (∞,n)-categories and dualizability in detail, and, time permitting, some extensions and variations.

# Fusion Category Symmetry II: Categoriosities at c = 1 and Beyond

Thorngren and Wang. https://arxiv.org/abs/2106.12577

# Matching higher symmetries across Intriligator-Seiberg duality,

Lee, Ohmori, Tachikawa. https://arxiv.org/abs/2108.05369

# Dan Freed lectures on “Topics in field theory and topological phases of matter”

Dan has given a series of lectures at the Korean Institute for Advanced Studies as part of a long running series organized by Minhyong Kim.

# Theo Johnson Freyd on “Operators and higher categories in quantum field theory”

Theo has given a lecture series at the Korean Institute for Advance Studies, as part of a long-running series organized by Minhyong Kim. The abstract for the talks read:

I. A complete mathematical definition of quantum field theory does not yet exist. Following the example of quantum mechanics, I will indicate what a good definition in terms could look like. In this good definition, QFTs are defined in terms of their operator content (including extended operators), and the collection of all operators is required to satisfy some natural properties.

II. After reviewing some classic examples, I will describe the construction of Noether currents and the corresponding extended symmetry operators.

III. One way to build topological extended operators is by “condensing” lower-dimensional operators. The existence of this condensation procedure makes the collection of all topological operators into a semisimple higher category.

IV. Topological operators provide “noninvertible higher-form symmetries”. These symmetries assign charges to operators of complementary dimension. This assignment is a version of what fusion category theorists call an “S-matrix”.

V. The Tannakian formalism suggests a way to recognize higher gauge theories. It also suggests the existence of interesting higher versions of super vector spaces with more exotic tangential structures.

# GCS: Kick-Off Meeting

October 11-13, 2021

**Simons Center for Geometry and Physics** (Stony Brook, NY), **International Centre for Mathematical Sciences** (Edinburgh, UK), and **Cyberspace**

Videos are available on the SCGP video repository.

If you are interested in attending this event from cyberspace you are welcome! Please register here

# Schedule

Indicated times are New York / Edinburgh. The program for the event with title and abstracts can be found below.

### MONDAY

9 / 14 Welcome and Introduction (Teleman, Del Zotto)

9:30 / 14:30 * Discussion: What is QFT?* (Freed, Seiberg)

10:30 / 15:30 Coffee

11 / 16 Scheimbauer (Zoom)

12 / 17 Kitaev (live SCGP)

1 Lunch / 18 Dinner

2:30 / 19:30 Hopkins (live SCGP)

3:30 Tea / 20:30 Scottish Tea

4 / 21 Kapustin (Zoom)

5 / 22 free/ad hoc/informal discussions

### TUESDAY

9 / 14 Check-in with ICMS, free discussion

9:30 / 14:30 García Etxebarria (live ICMS)

10:30 / 15:30 Coffee

11 / 16 Plavnik (live SCGP)

12 / 17 Xiao-Gan Wen (Zoom)

1 Lunch / 18 Dinner

2:30 / 19:30 ** Discussion: Non-invertible symmetries **(Komargodski, Ohmori, Shao,Thorngren)

3:30 Tea / 20:30 Scottish Tea

4 / 21 Gaiotto (Zoom)

5 / 22 free/informal/ad hoc discussion

### WEDNESDAY

9 / 14 Check-in with ICMS

9:30 / 14:30 ** Discussion: Perspectives on gauge theories** (Moore, Nekrasov)

10:30 / 15:30 Coffee

11 / 16 Schäfer-Nameki (live ICMS)

12 / 17 Cordova/Dumitrescu (live SCGP)

1 / 18 Closing remarks, Lunch/Dinner, and Goodbyes

# Program

## Discussion sessions

**What is quantum field theory?** – *Dan Freed and Nathan Seiberg*

**Non-invertible symmetries** – *Zohar Komargodski, Kantaro Ohmori, Shu-Heng Shao, and Ryan Thorngren*

**Perspectives on gauge theories** – *Greg Moore and Nikita Nekrasov*

## Guest Lectures

**Davide Gaiotto:** **Condensation of topological phases**

I will review an higher-dimensional generalization of the notion of projector introduced in my work with Theo Johnson-Freyd.

**Anton Kapustin:** **A local Noether theorem for quantum lattice systems and topological invariants of gapped states**

In field theory, conserved currents have well-known ambiguities. Thanks to the Poincare lemma, these ambiguities are physically harmless. Similar issues arise for lattice systems, but have not been explored previously. I will explain some general results which both ensure the existence of local currents on a lattice and describe the corresponding ambiguities. A starring role in this problem is played by a certain 1-shifted differential graded Lie algebra attached to a quantum lattice system. A similar 1-shifted DG Lie algebra can also be attached to any gapped state of a quantum lattice system. I explain how to use this algebraic structure to extract a topological invariant out of a gaped state of a 2d lattice system invariant under a U(1) symmetry. This invariant is the zero-temperature Hall conductance. This is joint work with Nikita Sopenko.

**Alexei Kitaev: ****Short-range entangled quantum states.**

This ongoing work aims to understand topological properties of ground states of gapped lattice Hamiltonians. In the special case of free-fermion systems, the homotopy type of the space of states is given by a shifted K or KO spectrum (depending on imposed symmetry). I will consider more general short-range entangled states, focusing on Bose systems with no symmetry. By definition, short-range entangled states are “r-constructible” and “(2r,epsilon)-pure”, where r is some length characterizing the extent of entanglement and epsilon is an error parameter. Some important properties include invertibility (i.e. the existence of an “anti-state”), gluing, and error reduction. Using this toolkit, one can, hopefully, show that the space of short-range entangled states is an Omega-spectrum.

*Sakura Schäfer-Nameki: *Generalized Symmetries in 5d and 6d

I will give an overview of recent developments in 5d and 6d superconformal field theories, describing their higher-form symmetries, as we all as higher-group structures.

Most of the analysis will be based on the geometric realization of these field theories in M-theory or F-theory on canonical three-fold singularities, and we will discuss how the generalized symmetries are imprinted in the underlying geometry.

**Xiao-Gan Wen:** **A categorical view of symmetry and a holographic view of symmetry**

Symmetry are usually described by groups or higher groups. Here I will described a more general view of symmetry in terms of fusion higher category. Symmetries described by different groups and/or different fusion higher categories can be equivalent. There is an even better way to describe symmetries in terms of braided fusion higher category, ie in terms of topological order in one higher dimension. The equivalent symmetries will be described by the same braided fusion higher category (ie the same topological order in one higher dimension).

## Lectures from our collaboration

*Clay Córdova/Thomas Dumitrescu: *Higher Symmetry in Gauge Theory

We will review a few of the many ways in which higher form and higher group symmetries arise in quantum field theory and how they can be used to analyze and organize renormalization group flows. For concreteness, we focus on non-supersymmetric gauge theory examples in four dimensions. In addition to recent progress, we will also highlight some open problems of possible mathematical and physical interest.

**Iñaki García Etxebarria:** **Categorical Symmetries and String Theory**

String theory provides a way to associate field theories to singular geometries. The resulting class of theories is very rich but the individual theories are often poorly understood, and in particular we generically don’t know how to define them starting from a Lagrangian. In this talk I will review part of what we know about deriving the symmetry structure of this class of theories from the geometry of their string theory construction.

*Mike Hopkins: *Topology and quantum field theory

*Julia Plavnik: *Gauging, condensation and zesting as quantum symmetries

In this talk, we will present the zesting construction for modular categories. Zesting was first introduced in 2012 and further developed for applications to fermionic theories in 2016. We will give some examples and properties of this construction and compare it with other constructions of modular categories like gauging and condensation.

*Claudia Scheimbauer: *Higher categorical tools for defects and boundary theories

Nowadays we have many mathematical tools, ie higher categorical, tools to construct and study TQFTs, boundary and defect theories (coupling). In this talk we will give an overview of the state of the art and discuss applications to various examples, such as Reshetikin-Turaev/Chern-Simons theory and lattice field theory and gauge theory.

** Curators: **Michele Del Zotto, Thomas Dumitrescu, David Jordan, Constantin Teleman