mathematical string theory meeting

Previous southeastern regional mathematical string theory meetings:

Video of many of these talks can be found here, in the string theory folder.

- 25th meeting: Saturday September 23, 2023, at NCSU.
Schedule:
- Friday September 22: Optional informal dinner, starting at 7 pm,
at the Raleigh Times,
located at 14 E. Hargett St in downtown Raleigh, NC.
See e.g. here
for parking locations in downtown. If you want to join us, please RSVP
Eric Sharpe by Thurs Sept 21 at noon, so that he can make a suitable
reservation.
- Saturday September 23: All talks will be held in Riddick Hall,
room 314.
Group photos
here,
here.
- 10:00 - 11:00: Robert Bryant (Duke), "The G_2 Laplacian flow"
- Abstract: 7-manifolds with holonomy G_2 are important as background for M-theory, and understanding the compact solutions, possibly with singularities, is a significant goal of the subject. The G_2-Laplacian flow is the G_2-analog of the Kahler-Ricci flow for Calabi-Yau metrics in complex geometry. In this talk, I’ll give an introduction to the subject and describe the current state of knowledge, in particular some of the results and problems related to the study of solitons of the flow.
- Photos here, here, here, here, here, here

- 11:15 - 12:15: Changha Choi (Perimeter), "Deconfinement in three dimensional gauge theories"
- Abstract: One of the most important characterizations in gauge theory is the nature of confinement. What makes 3d gauge theory particularly captivating is its tendency to exhibit robust deconfinement in various scenarios. We elucidate how this phenomenon can sometimes be comprehended exclusively through the lens of symmetries and anomalies. Furthermore, to shed more light on the dynamics at play, we delve into the minimal supersymmetric Yang-Mills-Chern-Simons theory and initiate the semiclassical analysis by placing it on the small circle.
- Photos here, here, here

- 12:30 - 2:00: Lunch
- 2:00 - 3:00: Diana Vaman (UVA),
"Tree-level Graviton Scattering in the Worldline Formalism"
- Abstract: We use the worldline formalism to study tree-level scattering processes involving gravitons. A massless spin 2 particle is described by an N=4supersymmetric worldline action which is also O(4) symmetric. More generally, N=2S supersymmetric worldline actions exhibiting O(N) symmetry describe free spin S particles. Recently a BRST approach was used to construct the on-shell background graviton emission vertex from a graviton worldline. Nonetheless, an action describing the coupling of higher spin (S≥2) particles with generic background gravity is unknown. In this paper, we found that in order to reproduce Einstein's general relativity 3-point graviton vertex, interpreted as the emission of an off-shell graviton from the worldline, the coupling to background gravity must break the O(4) symmetry to O(2)×O(2). In addition to this symmetry-breaking feature, we also found that the coefficient β of the worldline action counterterm βR differs from previous results in the literature. By comparing the linearized graviton and photon emission vertex operators from different worldlines, we noticed that they obey a squaring relation. For MHV (Maximal Helicity Violating) amplitudes, these squaring relations among the linearized vertex operators directly result in double-copy-like relations between the scattering amplitudes.
- Unfortunately, Diana had to cancel, but she did send her slides.
- slides

- 3:15 - 4:15: Theodore Jacobson (UCLA),
"Emergent 1-form symmetries and confinement"
- Abstract: We discuss the conditions under which higher-form symmetries can emerge in various limits. Such symmetries can appear as one tunes microscopic parameters, such as the masses of charged particles, or in the long-distance limit of a fixed quantum field theory. In the latter case, a minimal requirement for a 1-form symmetry to emerge is that the would-be symmetry generators behave topologically at long distances, and that they have non-trivial correlation functions. These conditions are met when the would-be symmetry is spontaneously broken or involved in 't Hooft anomalies, in which case the emergent symmetries have dramatic effects on the ground state structure. We comment on the lack of emergent 1-form symmetry in the 't Hooft large N limit of QCD with fundamental quarks, as well as in the long-distance limit of QCD at fixed finite N with heavy quarks.
- slides
- Photos here, here

- 4:30 - 5:30: Mendel Nguyen (NCSU)

- 10:00 - 11:00: Robert Bryant (Duke), "The G_2 Laplacian flow"

- Friday September 22: Optional informal dinner, starting at 7 pm,
at the Raleigh Times,
located at 14 E. Hargett St in downtown Raleigh, NC.
See e.g. here
for parking locations in downtown. If you want to join us, please RSVP
Eric Sharpe by Thurs Sept 21 at noon, so that he can make a suitable
reservation.

- 24th meeting: Saturday April 8, 2023 at Virginia Tech.
Schedule:
- Friday Apr 7: Optional informal dinner at
Zeppoli's at 810 University City Boulevard in Blacksburg, at 7:30 pm.
- Saturday Apr 8: All talks will be held in Robeson Hall, room 210.
Group photo
here and
here.
Schedule below:
- 10:00 - 11:00: Ibrahima Bah (Johns Hopkins),
"Non-invertible symmetry, holography and branes"
- Abstract: In this talk I will discuss some general methods for realizing topological symmetry generators in holography. In particular I will present a specific realization of non-invertible symmetry generators and their fusion rules in holographic duals of SU(N)/Z_N N=1 SYM. This will be both from a bottom-up perspective from an effective theory in AdS5, and from a top-down perspective in terms of D-branes in AdS5 backgrounds.

- 11:15 - 12:15: Tristan Hubsch (Howard),
"Generalized Mirror Models Beyond Algebraic Toric Spaces"
- Abstract: Calabi-Yau hypersurfaces in toric (complex algebraic) varieties and their mirror models are well understood, including the gauged linear sigma model (GLSM) and other stringy corrections to their cohomology ring structures. That however is but the tip of the iceberg. Non-convex, flip-folded and multi-winding (but "regularly subdivisible") variants of polytopes and fans encode U(1)^n-equivariant (co)homology on smooth manifolds with GLSM U(1)^n-action that are generically not algebraic, but have well-defined Calabi-Yau hypersurfaces. Surprisingly, at least some of these generalizations already turned up within deformation families of otherwise well understood algebraic constructions.
- audio
- Slides: pdf, key

- 12:30 - 2:00: Lunch
- 2:00 - 3:00: Naomi Gendler (Cornell),
"The Visible Axiverse"
- Abstract: In this talk, I will review the construction of an ensemble of axion models arising from type IIB string theory on toric hypersurface Calabi-Yau threefold orientifolds. I’ll first recount the absence of a Peccei-Quinn quality problem in this landscape of theories, and then explain some of the observational constraints on these string theory axions, coming from dark matter bounds as well as axion-photon coupling experiments. Finally, I’ll explain a mechanism that suppresses axion-photon couplings compared to naive estimates, and present some preliminary data on these couplings.
- video

- 3:15 - 4:15: Yichul Choi (Stony Brook),
"Noninvertible Gauss Law and Axions"
- Abstract: In the past years, the notion of global symmetry in quantum field theory has gone through a rapid evolution to include generalized symmetries generated by topological defects of higher codimensions and/or with noninvertible fusion algebras. A prototypical example of a generalized global symmetry is the electric 1-form symmetry in free Maxwell theory. An electric 1-form symmetry is a modern, symmetry-based way to describe the Gauss law. In this talk, we will consider axion-Maxwell theory, where the presence of the axion-photon coupling explicitly breaks the naïve electric 1-form symmetry, hence making the Gauss law anomalous. We will see that, however, the electric 1-form symmetry can be resurrected if we give up invertibility. The noninvertible electric 1-form symmetry leads to a modified version of the Gauss law, which we call the noninvertible Gauss law.
- slides
- video (Note: audio doesn't begin until 2/3 through.)

- 4:30 - 5:30: Max Hubner (Univ Pennsylvania),
"The Branes Behind Generalized Symmetry Operators"
- Abstract: We discuss a new place to wrap branes. Given a QFT geometrically engineered in String/M-theory branes can be wrapped on asymptotic cycles of the internal space at metric infinity. Whenever the asymptotic cycles are formally of infinite volume the space-time dimensions of the wrapped branes support at best a topological field theory. Further, such `branes at infinity' are at infinite distance from the localized QFT and therefore interact with it only topologically. Overall, such wrappings construct topological operators in the QFT which we argue to generate generalized global symmetries. We give examples in well-known theories.
- video
- slides

- 10:00 - 11:00: Ibrahima Bah (Johns Hopkins),
"Non-invertible symmetry, holography and branes"

- Friday Apr 7: Optional informal dinner at
Zeppoli's at 810 University City Boulevard in Blacksburg, at 7:30 pm.
- 23rd meeting: Saturday October 8, 2022 at Duke University.
Videos of all the talks are available
here.
Group photos are
here,
here,
here,
here.
Schedule:
- Friday Oct 7: Informal dinner at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham. If you wish to join us,
aim to be there by 7:45 - 8 pm, and please let Eric Sharpe
know by Thursday Oct 6 around lunchtime, so that he can make a
reservation.
- Saturday Oct 8: (All talks will be at Duke University,
physics building room 119. Although the talks will be in-person, we will
also attempt to broadcast on zoom, details to appear later.)
- 10:00-11:00: Mithat Unsal (NCSU),
"Adiabatic continuity, anomaly preserving compactifications, and
calculable confinement"
- Abstract: I will describe the idea of adiabatic continuity which can be used to continuously connect strongly coupled gauge theories on R^4 to compactified gauge theories on R^2 x T^2 by using 't Hooft flux background. In this process, I will describe how to perform semi-classical fractional instanton analysis in the 't Hooft flux background in a general class of theories. In the weak coupling (small T^2) regime, properties such as confinement, chiral symmetry breaking, and multi-branch structure as a function of theta angle are semi-classically calculable. As opposed to common beliefs emanating from the 70s, which emphasize that these are necessarily strong coupling phenomena, all of them can be realized in weak coupling regime. I will mention the roles of fractional instantons, resurgence, and TQFT couplings, and state some open problems.
- slides

- 11:15-12:15: Daniel Robbins (University of Albany),
"Topological defects and decomposition"
- Abstract: Decomposition is the idea that a d-dimensional quantum field theory with a global (d-1)-form symmetry is equivalent to a disjoint union of quantum field theories. A rich source of examples comes from 2D orbifolds in which a subgroup of the orbifold group acts trivially on local operators. I will review that story using the language of topological defect operators and discuss the role of discrete torsion and anomalies. I will also briefly discuss theories in higher dimensions, and how decomposition plays a role in the fusion of condensation defects.
- slides

- 12:30-2:00: Lunch
- 2:00-3:00: Patrick Jefferson (MIT),
"Euclidean D3 instantons and O3 planes in 4D F-theory vacua"
- Abstract: In F-theory, O3 planes are understood to correspond to terminal Z2 singularities in the compactification space that do not admit crepant resolutions and are hence difficult to analyze using classical tools in complex and algebraic geometry. I will describe a conjectural algorithm for analyzing the Hodge diamonds and intermediate Jacobians of vertical divisors of elliptic Calabi-Yau fourfolds in the presence of terminal Z2 singularities. This algorithm, which circumvents many of the computational difficulties introduced by these singularities, has immediate applications for analyzing the contributions of Euclidean M5 instantons to the superpotential of 4D F-theory compactifications in the Sen limit. Based on forthcoming work with Manki Kim (MIT).

- 3:15-4:15: Callum Brodie (VT),
"Target Space Duality from Gauge-Gravity Pair Creation"
- Abstract: Unlike for Type II string theory, it is currently not known whether it is possible for compactifications of the heterotic string to pass through a topological transition. This is due to the added complication of a background gauge bundle, whose consistent path across a topological transition has so far eluded understanding. Separately, there has been the observation from the rich structure of GLSMs, of the phenomenon of 'target space duality', in which heterotic compactification on two topologically distinct geometries, carrying different gauge bundle backgrounds, can apparently give rise to the same external physics. In this talk, I will provide a novel consistent description for how the background heterotic gauge bundle can traverse a topological transition, and show that this process precisely connects pairs of target space dual theories.
- slides

- 4:30-5:30: James Wheeler (Duke),
"A Dual Approach to Defining Black Holes"
- Abstract: I would like to discuss a novel approach to defining black holes in classical General Relativity in a manner that demands no constrictive structure of the spacetime. In particular, we will not require asymptotic flatness or any other such global hypotheses, save standard causality conditions. Even so, the subset we identify as the black hole has a natural global structure and is designed to optimally reflect intuitive physical notions as to what the term should mean with respect to the causal structure of spacetime at large. The approach outlines a program which may be rigorously carried through in a number of ways (similar to how there are various ways to technically realize the standard 'complement of the past of future infinity'), of which we will emphasize one as being most natural.
- slides

- 10:00-11:00: Mithat Unsal (NCSU),
"Adiabatic continuity, anomaly preserving compactifications, and
calculable confinement"

- Friday Oct 7: Informal dinner at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham. If you wish to join us,
aim to be there by 7:45 - 8 pm, and please let Eric Sharpe
know by Thursday Oct 6 around lunchtime, so that he can make a
reservation.
- Attempted 23rd meeting:
Cancelled b/c of covid pandemic. Below is the schedule
we had planned for this meeting, which was to be held at UVA on
the weekend of March 13-15, 2020, as part of an AMS spring sectional meeting.
Schedule: All talks will be held in Nau Hall, room 241. (The schedule is also listed here. If the room assignment changes, the correct assignment will be posted there.)

- Saturday March 14:
- 8:00-8:45: Lara Anderson (VT),
"New aspects of heterotic geometry"
- Abstract: In this talk I will describe new aspects of the total geometry of heterotic string compactifications – consisting of holomorphic, poly-stable vector bundles over Calabi-Yau manifolds. In particular, we will consider the case that the bundle/manifold geometry arises from a (0,2) Gauged Linear Sigma Model (GLSM). We demonstrate that Calabi-Yau manifolds arising as complete intersections in toric varieties and bundles defined via the monad construction over them have a simple combined toric description. We use this description to try to shed new light on (0,2) heterotic dualities.

- 9:00-9:45: James Gray (VT),
"Chern-Simons and Heterotic Superpotentials"
- Abstract: Compactifications of Heterotic theories on Calabi-Yau manifolds have a Chern-Simons like contribution to their fourdimensional superpotential. In this talk I will discuss some aspects of computations and general theory behind understanding this often ignored contribution to the effective theory of such constructions.

- 10:00-10:20: Wei Cui (VT),
"Numerical Ricci-Flat Metrics and Curvature Hierarchies in Calabi-Yau Manifolds"
- Abstract: We will discuss the application of numerical approximations to Ricci-flat metrics in searching for hierarchies of curvature scales on Calabi-Yau manifolds. Knowledge of such hierarchies is central to understanding the regimes of validity of string effective theories. We show that numerical methods can be effective at studying these issues and illustrate our discussion with some explicit examples.

- 10:30-10:50: Hao Zou (VT),
"Gauged Linear Sigma Models for Symplectic Grassmannians"
- Abstract: In this talk, I will discuss two-dimensional gauged linear sigma models realizing symplectic Grassmannians. After describing the construction of the GLSMs themselves, I will explain how the Coulomb branch computations in such GLSMs reproduce known ordinary and equivariant quantum cohomology ring relations. Similar constructions and analysis can also be used for more general isotropic spaces, for example, orthogonal Grassmannians and the G2 flag manifold.

- 3:00-3:45: Theo Johnson-Freyd (Perimeter),
"A secondary invariant of the elliptic genus" -- UPDATE: cancelled.
- Abstract: The elliptic genus is a powerful deformation invariant of 2d SQFTs: if it is nonzero, then it protects the SQFT from admitting a deformation to one with spontaneous supersymmetry breaking. This talk will describe a ”secondary” invariant that goes beyond the elliptic genus, protecting SQFTs with vanishing elliptic genus. Our invariant relates directly to mock modularity. It furthermore supports the hypothesis that the space of minimally supersymmetric 2d SQFTs providesa geometric model for the spectrum of topological modular forms.

- 4:00-4:45: William Linch (Texas A-M),
"Off-shell Supersymmetry and the M-theory Effective Action"
- Abstract: The leading part of the M-theory low-energy effective action has been conjectured to be the minimal supersymmetric completion of a certain curvature-to-the-fourth correction to eleven-dimensional supergravity. This idea is difficult to exploit, because a component Noether procedure would have an infinite number of steps of ever-higher order in the curvature expansion. In an off-shell superspace, the supersymmetry closes independently of the interactions, but any 11D, N=1 superspace would put the theory on-shell. In this talk, I will describe an ongoing program to construct an 11D, N = 1/8 supergeometry that is potentially “sufficiently off shell” to supersymmetrize the leading M-theory correction to the eleven-dimensional supergravity action.

- 8:00-8:45: Lara Anderson (VT),
"New aspects of heterotic geometry"
- Sunday March 15:
- 9:00-9:45: Anatoly Dymarsky (Kentucky),
"Quantum KdV hierarchy at large central charge"
- Abstract: I will review recent progress of ”solving” quantum KdV hierarchy at large central charge, which includes finding thespectrum, the transfer matrix, and the generalized character. I will also discuss how explicit answers in the large central charge limit can shed light on modular properties of the generalized 2d CFT partition function and be used to establish Eigenstate Thermalization Hypothesis.

- 10:00-10:45: Falk Hassler (Texas A-M),
"Generalised Quotients"
- Abstract: Generalised Scherk-Schwarz reductions are a powerful tool to construct consistent truncations in generalised geometry. Recently, it turned out that they are also closely related to Poisson-Lie T-duality. However, the most general form of Poisson-Lie T-duality, the dressing coset construction, can not be implemented in terms of a generalised Scherk-Schwarzansatz. I will show that implementing it in generalised geometry leads to a natural extension of the generalised Scherk-Schwarz ansatz which comes with many new features: 1) Partial or full breaking of SUSY which allows to find many new examples of generalised Kaehler or Calabi-Yau Manifolds. 2) Singular backgrounds with localised sources. 3) Localised vector multiplets while still resulting in consistent truncations.

- 11:00-11:45: Du Pei (Harvard),
"BPS States and Invariants of 3-Manifolds"
- Abstract: String theory predicts a class of new homological invariants of 3-manifolds that generalizes the Gopakumar-Vafa and Ooguri-Vafa invariant. I will review recent progress in understanding these new invariants, focusing on their “decategorifications” that take the form of q-series with integer coefficients.

- 9:00-9:45: Anatoly Dymarsky (Kentucky),
"Quantum KdV hierarchy at large central charge"

- Saturday March 14:
- 22nd meeting: Saturday November 2, 2019, at Duke University.
Group photos here,
here,
here.
Schedule:
- Friday Nov 1: Informal dinner at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham. If you wish to join us,
aim to be there by 7:45 - 8 pm.
- Saturday Nov 2: (All talks will be at Duke University,
physics building room 119.)
- 10:00-11:00: Monica Kang (Caltech), "Entanglement wedge reconstruction and holographic relative entropy"
- Abstract: I will discuss bulk reconstruction and holographic relative entropy in infinite-dimensional Hilbert spaces, which is the natural setting to study the consequences of the Reeh-Schlieder theorem. By using infinite-dimensional von Neumann algebras as the local operator algebra of such theories, I will discuss the relation between bulk reconstruction and the equivalence of bulk and boundary relative entropies. As an example, I will describe a toy model of an error correcting code that encodes a bulk type II1 von Neumann algebra in a boundary type II1 von Neumann algebra.
- photo, photo, photo

- 11:15-12:15: Ho Tat Lam (P-ton),
"Anomalies in the Space of Coupling Constants and Their Dynamical Applications"
- Abstract: We will explain how the notation of an 't Hooft anomaly can be extended to a family of quantum field theories labeled by coupling constants such as the theta-angle in 4d gauge theories. We will use this idea to constrain the long-distance dynamics of the theories. We will also apply the same idea to constrain the dynamics of defects where coupling constants vary in spacetime. Several examples will be explained in details.
- photo, photo, photo

- 12:30-2: Lunch,
- 2:00-3:00: Yuya Tanizaki (NCSU),
"Discrete anomaly matching in QCD"
- Abstract: Recent renewed attention on anomaly matching elucidates new nonperturbative aspects of quantum field theories. Thanks to the discovery of generalization of global symmetry, we have a new class of anomaly that involves higher-form gauge fields. After a brief review of these developments, I would like to discuss its application for QCD with massless quarks. About QCD vacuum, we find a funny anomalous violation of baryon number symmetry, which excludes some exotic patterns of chiral symmetry breaking. We will also see that the same anomaly gives a nontrivial constraint in finite-temperature QCD phase diagram IF we introduce appropriate holonomy backgrounds, or imaginary chemical potentials.
- photo, photo, photo
- talk notes

- 3:15-4:15: Mithat Unsal (NCSU),
"Quantum distillations, semi-classics and mixed anomaly"
- Abstract: We propose a grading protocol which assigns global symmetry associated phases to states in the Hilbert space. Without modifying the Hilbert space, this changes the state sum, a process that we call quantum distillation. We describe the image of quantum distillation in terms of (non- dynamical) flavor holonomy dependence of (dynamical) gauge holonomy potentials, in QCD with Nf = Nc fundamental and one massive adjoint fermion on R^3 × S^1. The compactified theory possesses an exact zero-form color-flavor center symmetry for a special choice of flavor holonomy (under which Polyakov loop is charged), despite the absence of one-form center-symmetry. We prove that the CFC symmetry is stable at small-β. This is the opposite of the high-temperature limit of thermal theory and a dramatic manifestation of quantum distillation. We show chiral symmetry breaking at small S1 and that the vacuum structure of the theory on R^4 and R^3 × S^1 are controlled by the same mixed ’t Hooft anomaly condition.
- photo, photo

- 4:30-4:50: Mohsen Karkheiran (VT),
"Generalized Fourier-Mukai transform in Heterotic string/F-theory"
- Abstract: I'll talk about the assumptions and limitations of the standard spectral cover construction of vector bundles in Heterotic string theory and Heterotic/F-theory duality. However, it is possible to deal with such limitations by using more formal descriptions of Fourier-Mukai functors. I’ll give some examples in small instanton transitions and 4D EFT’s that were missed in the standard approach.
- photo, photo
- slides (pdf)

- 4:50-5:10: Juntao Wang (VT),
"Chern-Simons Terms and Heterotic Superpotentials"
- Abstract: In this talk I will discuss some recent progress on the Chern-Simons like superpotential which shows up in the four dimensional effective theory of compactifications of the Heterotic String on Calabi-Yau manifolds. I will discuss how the physical and mathematical definitions of the superpotential correspond, and, based on this, I will discuss its computation in non-trivial examples.
- photo, photo
- slides (pptx)

- 5:10-5:30: Rob Vandermolen (South Carolina),
"Curious Kernels for GLSMs"
- Abstract: An Artin stack is a sophisticated generalization of a variety, which encodes the idea of equivariant geometry. A simple example is a vector space carrying a linear action of a Lie group. In String Theory this data defines a Gauged Linear Sigma Model. A GLSM is a kind of 2-dimensional quantum field theory, but it's a gauge theory, which means it's based on sections of, and connections on, a vector bundle. The class of GLSMs that this talk will be concerned with are specified by the data of a complex vector space V carrying a representation of a linear algebraic group G, these give the fibre and the structure group of the vector bundle. Getting at this equivariant structure of a GLSM we use the tool of Geometric Invariant Theory quotients, in this theory there are different possible quotients which arise from different limits. In this talk we will explore a new program using integral transformations to study how the B-branes of these GLSMs change under this variation-of-GIT. This program is inspired by recent work of Ballard, Diemer, Favero (2017) and work of Ballard, Chidambaram, Favero, McFaddin, and myself (2019), these papers provide a new class of kernels for realizing the derived equivalence for many interesting birational transformations.
- photo, photo

- 10:00-11:00: Monica Kang (Caltech), "Entanglement wedge reconstruction and holographic relative entropy"

- Friday Nov 1: Informal dinner at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham. If you wish to join us,
aim to be there by 7:45 - 8 pm.
- 21st meeting: Saturday April 20, 2019, at Duke University.
Group photos
here,
here,
here.
Schedule:
- Friday April 19: informal dinner, starting at 7:30 pm at
Sitar Indian Cuisine
at 3630 Durham Chapel Hill Blvd in Durham, NC.
- Saturday April 20: (All talks will be at Duke University,
physics room 130.)
- 10:30-11:30: Onkar Parrikar (U-Penn),
"Quantum Information, Machine Learning and Knot Theory":
- Abstract: We will discuss applications of quantum information theory and machine learning to knot theory. In the first part, we will use ideas from quantum information theory such as entanglement entropy to study properties of the colored Jones polynomial of links. In particular, we will prove that torus links have a very fragile, "GHZ-like" entanglement structure. On the other hand, we will present evidence in favor of the conjecture that hyperbolic links have a more robust "W-like" entanglement structure. In the second part of the talk, we will show that a simple 2-layer neural network can predict the hyperbolic volume of a knot from its Jones polynomial with a very high (97.5%) accuracy. This suggests a deeper relation between the Jones polynomial and the hyperbolic volume, perhaps pointing to a generalization of the volume conjecture.
- photo, photo, photo, photo
- talk slides (pdf)

- 11:45-1:15: Lunch,
- 1:30--2:30: Louise Anderson (Stanford),
"Quantum phase transitions in 3D Chern-Simons matter theories":
- Abstract: I will review how the partition function of 3d N=2 quiver theories on S^3 can be reduced to a matrix model using supersymmetric localisation. We will then illustrate techniques to solve these in the large N-limit. We will consider two examples of mass-deformed Chern-Simons theories that preserve N=2 supersymmetry: mass-deformed ABJ(M) theory and mass-deformed Chern-Simons theory. We then calculate the free energy as a function of the deformation parameters, and for general theories, we find a series of quantum phase transitions in the infinite-volume limit. A particularly interesting case is that of mass-deformed ABJM theory, where the holographic dual is known. We find no sign of phase transitions for physical values of the level and gauge group, which agrees with holographic results.
- photo, photo, photo, photo

- 3:00-4:00: Travis Maxfield (Duke),
"Mirror Symmetry and Partition Functions":
- Abstract: Localization methods have produced explicit expressions for the sphere partition functions of (2,2) superconformal field theories. The mirror symmetry conjecture predicts an IR duality between pairs of Abelian gauged linear sigma models, a class of which describe families of Calabi-Yau manifolds realizable as complete intersections in toric varieties. We investigate this prediction for the sphere partition functions and find agreement between that of a model and its mirror up to the scheme-dependent ambiguities inherent in the definitions of these quantities. (Based on 1902.05552.)
- photo, photo, photo

- 10:30-11:30: Onkar Parrikar (U-Penn),
"Quantum Information, Machine Learning and Knot Theory":

- Friday April 19: informal dinner, starting at 7:30 pm at
Sitar Indian Cuisine
at 3630 Durham Chapel Hill Blvd in Durham, NC.
- 20th meeting: Saturday October 13, 2018, at James Madison University.
Group photos
here,
here,
here,
here.
Schedule:
- Friday Oct 12: optional dinnner at, tentatively,
Clementine Cafe (153 S Main St,
Harrisonburg, VA), at 7:30 pm. (If the restaurant's parking lot is full,
note that there is a
municipal parking deck
on the other side of the same block, and after 7 pm, no time limit.)
- Saturday Oct 13: (All talks will be in Physics-Chemistry building room
PHCH2212.)
- 10:00-11:00: Po-Shen Hsin (Princeton),
"2-group global symmetry in QFT":
- Abstract: Quantum field theory can have 2-group symmetry that combines 0-form and 1-form symmetries. I will give examples of QFT with 2-group symmetry. In particular, I will discuss the anomaly of 2-group symmetry, and explore its consequences for the renormalization group flow.
- talk slides (pdf)

- 11:15-12:15: Mykola Dedushenko (Caltech),
"Gluing in QFT and Boundary Localization":
- Abstract: I will revisit the cutting an gluing law in local quantum field theory. In particular, gluing operation in Lagrangian theories can be represented as a path integral over a space of certain 'polarized' boundary conditions. This path integral, although being terribly non-local, can sometimes be simplified in supersymmetric theories using the localization techniques. This allows to obtain interesting gluing formulas that can be further applied to various problems, as will be discussed in more details during the talk.
- photo, photo, photo, photo, photo, photo, photo

- 12:30-2: Lunch,
- 2:00-3:00: Cynthia Keeler
(Arizona State),
"Partition Functions via Quasinormal Mode Methods: AdS, Warped AdS, and
Large Dimensions":
- Abstract: After a review of the quasinormal mode method for partition function calculation developed by Denef, Hartnoll, and Sachdev, we extend the method to consider even-dimensional AdS spaces, Warped AdS spaces, and black holes in the large dimension limit. If time permits, we will also discuss the relationship between the quasinormal mode method and the heat kernel method.
- photo, photo, photo, photo
- talk slides (pdf)

- 3:15-4:15: Fedor Popov (Princeton),
"Traversable wormholes in four dimensions":
- Abstract: We present a wormhole solution in four dimensions. It is a solution of an Einstein Maxwell theory plus charged massless fermions. The fermions give rise to a negative Casimir-like energy, which makes the wormhole possible. It is a long wormhole that does not lead to causality violations in the ambient space. It can be viewed as a pair of entangled near extremal black holes with an interaction term generated by the exchange of fermion fields.
- photo, photo, photo
- talk slides (pptx)

- 4:30-5:30: Andy Royston
(Penn State Fayette).
"Wall crossing from Dirac Zero modes":
- Abstract: In the semiclassical quantization of 4D N=2 super-Yang-Mills, (framed) BPS states are represented by zero mode wavefunctions of certain Dirac-like operators on the moduli space of (singular) monopoles. A direct analysis of these Dirac operators utilizing the asymptotic metric on monopole moduli space leads to a physically intuitive derivation of the primitive wall-crossing formula for BPS states. The derivation holds modulo a technical assumption about the Fredholm properties of these operators. Proving this assumption and showing how it must be modified in the non-primitive case is an open problem that makes contact with recent developments in the mathematics literature on compactifications of monopole moduli spaces on manifolds with corners. Additionally, the physics derivation leads to a surprising prediction: the existence of completely stable non-BPS boundstates. This talk is based on work done in collaboration with Greg Moore and Daniel Brennan.
- photo, photo, photo, photo, photo, photo

- 10:00-11:00: Po-Shen Hsin (Princeton),
"2-group global symmetry in QFT":

- Friday Oct 12: optional dinnner at, tentatively,
Clementine Cafe (153 S Main St,
Harrisonburg, VA), at 7:30 pm. (If the restaurant's parking lot is full,
note that there is a
municipal parking deck
on the other side of the same block, and after 7 pm, no time limit.)
- 19th meeting: Saturday April 7, 2018, at Duke University, in
physics room 130. Group photos
here,
here,
here.
Schedule:
- 10:00-11:00: Daniel Roberts (IAS / FAIR),
"Chaos and the growth of operators"
- Abstract: We will consider (a very small subset of) recent work on quantum chaos. We will connect the butterfly effect to the growth of operators through the lens of different model quantum systems: spin chains, holographic CFTs, and the SYK model. We will also enumerate different diagnostics for chaos including out-of-time-order correlation functions (OTOCs) and discuss different speeds at which information can propagate in quantum systems.
- photo, photo, photo, photo, photo

- 11:15-12:15: Laura Schaposnik (Univ Illinois Chicago),
"On Cayley and Langlands type correspondences for Higgs bundles"
- Abstract: The Hitchin fibration is a natural tool through which one can understand the moduli space of Higgs bundles and its interesting subspaces (branes). After reviewing the type of questions and methods considered in the area, we shall dedicate this talk to the study of certain branes which lie completely inside the singular fibres of the Hitchin fibrations. Through Cayley and Langlands type correspondences, we shall provide a geometric description of these objects, and consider the implications of our methods in the context of representation theory, Langlands duality, and within a more generic study of symmetries on moduli spaces.
- photo, photo, photo, photo, photo

- 12:30-2: Lunch
- 2:00-3:00: Fei Yan (UT Austin),
"Line defect Schur indices, Verlinde algebras and U(1) fixed points"
- Abstract: Given a 4d N=2 superconformal field theory, one could consider Schur index in presence of a half line defect L. Recently Cordova-Gaiotto-Shao found that such index admits an expansion in terms of characters of the chiral algebra introduced by Beem et al. In this talk I will report a puzzling new feature of this expansion: the q → 1 limit of the expansion coefficients is linearly related to the vacuum expectation values < L > in the U(1)_r-invariant vacua of the theory compactified on a circle. This relation can be expressed as a commutative diagram involving three algebras: the OPE algebra of line defects, the algebra of functions on the U(1)_r-invariant vacua, and a Verlinde-like algebra associated to the chiral algebra. This is joint work with Andy Neitzke.
- photo, photo, photo, photo, photo

- 3:15-4:15: Eugene Rabinovich (UC Berkeley),
"A Mathematical Discussion of the Axial Anomaly in the Batalin-Vilkovisky Formalism"
- Abstract: One general perspective on anomalies is that they are a measure of the obstruction to giving the partition function a well-defined value. Using the Batalin-Vilkovisky formalism---as developed by Costello and Gwilliam---we give a mathematical justification of this perspective for the case of perturbative anomalies of the massless free fermion. In particular, for the case of the axial anomaly, we recover the index of the Dirac operator as the relevant obstruction.
- photo, photo, photo, photo, photo, photo, photo, photo

- 10:00-11:00: Daniel Roberts (IAS / FAIR),
"Chaos and the growth of operators"
- 18th meeting: Saturday October 7, 2017, at VT in Blacksburg, VA.
Group photos
here,
here,
here.
Schedule:
- Friday October 6, 2017: Optional informal dinner, starting at 7:15 pm
at
Zeppoli's, at
810 University City Boulevard in Blacksburg.
(Second right from Price's Fork intersection, located just behind the
Verizon store.)
- Saturday October 7, 2017 at VT, in Robeson 210:
- 10:30-11:30: Travis Maxfield (Duke), "A new twist on theories with 8 supercharges,"
video
- Abstract: I will review results from the last few years on novel protected sectors in some theories with 8 supercharges, and I will describe ongoing efforts to extend these results to new theories/new domains.
- photo, photo, photo, photo

- 11:30-1: Lunch
- 1-2: Jennifer Lin (IAS), "Entanglement and spacetime,"
video,
slides
- Abstract: I'll review the evidence, primarily from the Ryu-Takayanagi formula in AdS/CFT, for the idea that spacetime emerges from the entanglement of some underlying quantum system. I’ll then discuss ongoing attempts to understand what the Ryu-Takayanagi formula might be counting from a bulk point of view.
- photo, photo, photo, photo

- 2:10-3:10: Tristan Hubsch (Howard), "Evidence for Infinitely Diverse Non-Convex Mirrors,"
video,
slides
- Abstract: Calabi-Yau hypersurfaces in non-Fano varieties are now a little over two years young, their toric siblings about half of that. Their defining polynomials include rational monomials, and are encoded by non-convex polytopes. Nevertheless, the phases of the corresponding gauged linear sigma models and an increasing number of their classical and quantum characteristics are found to be just as computable. This survey will focus on Batyrev-Hodge numbers, transposition mirror models and discriminants, eying also Yukawa couplings and other results within reach. Showcasing Calabi-Yau hypersurfaces in Hirzebruch n-folds shows this class of constructions to be infinitely vast, with infinite diversity for string theory.
- photo, photo, photo, photo, photo

- 3:20-4:20: Wei Gu (VT), video, slides

- 10:30-11:30: Travis Maxfield (Duke), "A new twist on theories with 8 supercharges,"
video

- Friday October 6, 2017: Optional informal dinner, starting at 7:15 pm
at
Zeppoli's, at
810 University City Boulevard in Blacksburg.
(Second right from Price's Fork intersection, located just behind the
Verizon store.)
- 17th meeting: April 8, 2017, at UNC-CH, in Chapel Hill, NC.
Group photos
here,
here,
here,
here,
here,
here.
Schedule:
- Fri Apr 7: Dinner at Top of the Hill in Chapel Hill, starting at 7:30 pm. This is completely optional, a fun event for those who are in the area. If you want to attend, please inform Eric Sharpe by Wed Apr 5 at 5 pm, so that he can make reservations.
- Sat Apr 8 in Frederick Brooks 141 (faculty conference room), also
accessible from Sitterson Hall,
at UNC-CH:
- 10:30-11:30: Maria Rodriguez (Utah State), ``Blandford-Znajek effect without plasma''
- 11:30-1: Lunch
- 1-2: Tom Rudelius (Harvard), ``6D SCFTs and Group Theory,''
slides
- Abstract: Superconformal field theories in six dimensions (6D SCFTs) have surprising connections to objects in group theory. In this talk, we will explore the relationship between 6D SCFTs, automorphism groups of matrices, and various classes of homomorphisms.
- photo, photo, photo, photo, photo, photo, photo, photo

- 2:10-3:10: Falk Hassler (UNC-CH), ``Surprisingly Complex Punctures from a Dynamical System''
- Abstract: Theories of class S are 4D N=2 SCFTs which result from the compactification of 6D N=(2,0) SCFTs on punctured Riemann surfaces. They provide a geometric perspective on S-duality and are essential in the AGT correspondence. I will present the first step in extending this construction to N=1. To this end, we discuss the punctures relevant in the compactification of the world-volume theory of M5-branes probing an ADE-singularity. They are closely related to the time evolution of a dynamical system and exhibit a surprisingly rich and complex structure compared to N=2.
- photo, photo, photo

- 3:20-4:20: Mboyo Esole
(Northeastern),
``Anomaly free SO(3), SO(5), and SO(6) gauge theories from F Theory''
- Abstract: Orthogonal groups in F Theory are delicate to define as they require a condition on the Mordell-Weil group of the generic elliptic fiber to distinguish them from spin groups. Moreover, the orthogonal groups discussed in the literature are SO(7+k) with k>0. In this talk, I will discuss the explicit construction of lower rank orthogonal groups in F Theory, classify their singular fibers and matter content in 4, 5, and 6 dimensional spacetimes. I will also present the details of their uplift from 5 to 6 dimensions, the cancellations of 6 dimensional anomalies and the structure of the Coulomb phases of the five dimensional theory. All this will be presented as an exercise in intersection theory using a new pushforward theorem for Chow rings of blowups.
- photo, photo, photo, photo, photo, photo, photo, photo, photo

- 16th meeting: November 12-13 2016 at NCSU, in Raleigh, NC, held as the
`Mathematical string theory' special
session at the
fall
southeastern sectional meeting of the AMS.
Schedule:
- Friday November 11:
In lieu of meeting for dinner, I encourage everyone to spend some time
on Friday evening at the
NC Museum of Art, which is open until
9 pm on Friday evenings, and whose main collection is free to visit.
The museum has a small restaurant (the Iris restaurant), as well as a
separate small coffee bar in the west building.
- Saturday November 12 at NCSU, talks in Park Shops room 215:
Update Nov 11
- 7:30am-4pm: Registration (SAS hall lobby)
- 9:00-9:45: Shu-Heng Shao (Institute for Advanced Study), ``Superconformal Indices, BPS Particles, and Chiral Algebras,'' video. (Moved from 8 am) Photos from his talk here, here.
- Jonathan Mboyo Esole: cancelled
- 10:00-10:45: Marco Aldi (VCU), ``Generalized CRF structures and T-duality,'' video (incomplete). Photos from his talk here, here.
- 11:00-3:00: Lunch break and AMS talks
- 3:00-3:45: Michele Del Zotto (Simons Center Stony Brook), ``On Exceptional Instanton Strings,'' video. Photos from his talk here.
- 4:00-4:45: Oscar Chacaltana (IFT Brazil, visiting Johns Hopkins), ``Defects of the 6D (2,0) theories and class-S theories of type E,'' video. Photos from his talk here.

- Sunday November 13 at NCSU, talks in Park Shops room 215:
- 8:00-8:45: He Feng (VT), ``New Evidence for (0,2) Target Space Duality,'' slides, video part 1, video part2. Photos from her talk here, here, here.
- 9:00-9:45: Pavel Putrov (Institute for Advanced Study), ``Exact solutions of N=(0,2) 2d Landau-Ginzburg models,'' slides, video. Photos from his talk here, here, here.
- 10:00-10:45: Savdeep Sethi (Chicago), ``Quantum Rings from Duality,'' video (incomplete). Photos from his talk here.

- Friday November 11:
In lieu of meeting for dinner, I encourage everyone to spend some time
on Friday evening at the
NC Museum of Art, which is open until
9 pm on Friday evenings, and whose main collection is free to visit.
The museum has a small restaurant (the Iris restaurant), as well as a
separate small coffee bar in the west building.

- 15th meeting: Saturday April 23, 2016. Group photos
here,
here,
here.
Schedule:
- Friday April 22: Informal dinner, starting at 7 pm at
Zeppoli's, at
810 University City Boulevard in Blacksburg.
(Second right from Price's Fork intersection, located just behind the
Verizon store.)
- Saturday April 23 at VT, in Robeson 210:
- 9:30 - 10:30: Paul Oehlmann (Bonn, VT), ``Mordell-Weil Torsion in the Mirror of Multi-Sections,'' video, slides. Photos from his talk here, here, here, here, here.
- 10:40 - 11:40: Ilarion Melnikov (JMU), ``Relevant deformations and c-extremization,'' video.
- 11:40-1:15: Lunch. Options include Macado's (922 University City Blvd, B-burg) and India Garden Restaurant (210 Prices Fork Road, B-burg).
- 1:15-2:15: Taizan Watari (IPMU, Harvard), ``Heterotic--Type IIA dualtiy and degeneration of K3 surface,'' video, slides.
- 2:30-3:30: Louise Dolan
(UNC-CH),
``General Solution of The Scattering Equations,''
video.
- Abstract: The scattering equations, originally introduced by Fairlie and Roberts in 1972 and more recently shown by Cachazo, He and Yuan to provide a kinematic basis for describing tree amplitudes for massless particles in arbitrary space-time dimension, have been reformulated in polynomial form. The scattering equations for $N$ particles are equivalent to $N-3$ polynomial equations $h_m=0$, $1\leq m\leq N-3$, in $N-3$ variables, where $h_m$ has degree $m$ and is linear in the individual variables. Facilitated by this linearity, elimination theory is used to construct a single variable polynomial equations of degree $(N-3)!$ determining the solutions.
- Photos from her talk here, here, here, here, here.

- Friday April 22: Informal dinner, starting at 7 pm at
Zeppoli's, at
810 University City Boulevard in Blacksburg.
(Second right from Price's Fork intersection, located just behind the
Verizon store.)

- 14th meeting: Saturday October 24, 2015.
Group photo here.
Schedule:
- Friday October 23: Informal dinner, starting at 7:30 pm at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham NC.
- Saturday October 24 at Duke, in physics room 130:
- 9:30-10:30: Cyril Closset (Stony Brook),
``Localization on twisted spheres in two-dimensional gauge theories''
(slides,
video)
- Abstract: I will revisit the A-twisted gauged linear sigma model (GLSM) in the case of (2,2) supersymmetry in two dimensions, together with its Omega-background deformation. Exact results for correlation functions can be obtained in terms of residues on the Coulomb branch, which has a number of interesting applications. I will also consider the generalization to (0,2) supersymmetric GLSM.

- 10:40-11:40: Abhijit Gadde (IAS), ``Aspects of 2d (0,2) theories'' (slides, video)
- 11:40-1: Lunch
- 1-2: Chen Sun (VT), ``Rethinking gauge theory through Connes' noncommutative geometry'' (slides, video)
- 2:10-3:10: Daniel Park (Stony Brook, Rutgers),
``Towards finding all string vacua
in six dimensions''
(video)
- Abstract: I will review the efforts made towards approaching string universality in six dimensions and report recent "cartographic" developments on exploring the landscape of six-dimensional string vacua. A working conjecture is that all the six-dimensional string vacua can be constructed in F-theory, which leads to the problem of classifying all elliptically fibered Calabi-Yau threefolds. I will present some progress on classifying all the four-manifolds that can be used as a base of such threefolds.

- 3:20-4:20: Xin Gao (VT), ``Generalized Complete Intersection Calabi-Yau
(gCICY) Manifold and Its
Physical Applications''
(slides)
- Abstract: We present a generalization of the complete intersection in products of projective space (CICY) construction of Calabi-Yau manifolds. Their utility stems from the fact that they can be simply described in terms of a `configuration matrix', a matrix of integers from which many of the details of the geometries can be easily extracted. The generalization we present is to allow negative integers in the configuration matrices which were previously taken to have positive semi-definite entries. This broadening of the complete intersection construction leads to a larger class of Calabi-Yau manifolds than that considered in previous work. These new Calabi-Yau manifolds are complete intersections in (not necessarily Fano) ambient spaces with an effective anticanonical class. We find examples with topology distinct from any that has appeared in the literature to date. The new manifolds thus obtained have many interesting features. For example, we explore contributions to the superpotential and the structure of instantons wrapping effective divisors in Calabi-Yau fourfolds.

- 9:30-10:30: Cyril Closset (Stony Brook),
``Localization on twisted spheres in two-dimensional gauge theories''
(slides,
video)

- Friday October 23: Informal dinner, starting at 7:30 pm at
Sitar Indian Cuisine,
at 3630 Durham Chapel Hill Blvd in Durham NC.

- 13th meeting: Saturday April 11, 2015. Schedule:
- Friday April 10: Informal dinner tentatively at
The Pit (321 W. Geer St.) in
Durham, starting at 7 pm.
The Pit is located at the intersection of Geer St and Rigsbee Avenue, beside Fullsteam Brewery and across the street from Motorco Music Hall. There is a parking lot across the street also; however, access to the lot is from Geer St. There is also parking available in smaller lots elsewhere in the area, plus -- if you're willing to walk a bit -- there is a large lot at the 400 block of Morris St.

- Saturday April 11:
- 9:30-10:30: Philip Argyres (University of Cincinnati), ``Geometric constraints on the space of N=2 SCFTs'' (slides, video)
- 10:40-11:40: Sheldon Katz (University of Illinois), ``Topological string partition function on elliptically fibered Calabi-Yau threefolds and Jacobi forms''
- 11:40-1: Lunch
- 1-2: Diana Vaman (University of Virginia), ``Entanglement Hamiltonians for chiral fermions'' (slides)
- 2:10-3:10: Seung-Joo Lee (VT), ``BPS states, quiver invariants and mutations'' (slides)
- 3:20-4:20: Jirui Guo (VT), ``Triality of two-dimensional (0,2) theories'' (slides)

- Friday April 10: Informal dinner tentatively at
The Pit (321 W. Geer St.) in
Durham, starting at 7 pm.

- 12th meeting: Saturday October 25, 2014. Schedule:
- Friday October 24: informal dinner, meet at 6:30 pm at Dales Indian Cuisine, 811 North Ninth St, Durham. Parking is available in the gravel lot across the street from the restaurant.
- Saturday October 25 at Duke, in physics room 119:
- 10:15 - 11:15: Chris Beasley (Northeastern University),
``Self-Linking for Legendrian Knots''
- Abstract: I will discuss a new class of supersymmetric Wilson loop operators in pure N=2 Yang-Mills-Chern-Simons theory. These Wilson loops preserve one supercharge on-shell and wrap arbitrary Legendrian knots in the standard contact R^3. Conjecturally, perturbation theory produces a series of finite-type Legendrian invariants for the knot. These invariants can be analyzed by means of a new "perturbative" localization principle, which I illustrate at leading-order. This talk is based upon joint work with Brendan McLellan and Ruoran Zhang.

- 11:30-1: Lunch
- 1-2: Anindya Dey (UT Austin), ``Field Theory on Gibbons-Hawking Spaces''
- Abstract: The IR Lagrangian of an N=2 supersymmetric gauge theory compactified on R^3 x S^1, around a generic point of its moduli space, is a 3d sigma model with a hyperkahler target space. We consider a related problem of constructing the IR Lagrangian of an N=2 theory on a special family of circle fibrations over R^3 -- namely Gibbons-Hawking spaces. We propose that the answer is a novel deformation of the standard 3d hyperkahler sigma model and study the constraints imposed by supersymmetry on such a theory. In particular, supersymmetry implies that the contribution of the NUT center to the sigma model path integral must be a holomorphic section of a certain holomorphic line bundle over the hyperkahler target space. We illustrate various features of this deformed sigma model using certain examples involving Abelian gauge theories on Gibbons-Hawking spaces.

- 2:15-3:15: Chris Beem (IAS), ``Chiral symmetry algebras and superconformal field theories in four and six dimensions''
- Abstract: I will describe the identification of a supersymmetry-protected subalgebra of the operator algebra of any four-dimensional N=2 SCFT or six-dimensional (2,0) SCFT that takes the form of a two-dimensional chiral algebra. The structure of this protected chiral algebra reflects the physics of the parent four- or six-dimensional theory in interesting ways. In many cases the relevant chiral algebra can be given an economical description as a W-algebra. Applications of this structure include the derivation of new unitarity bounds for four-dimensional SCFTs with global symmetries and the computation of three-point functions of half-BPS operators in the (2,0) theories at finite central charge.

- 3:30-4:30: Falk Hassler (Munich),
``String Geometry Beyond the Torus,''
slides here
- Abstract: Besides propagating in target space like a point particle, a closed string is also able to wind around non-contractible circles. A direct consequence thereof is T-duality. In the textbook example, it identifies the closed string dynamics on a large and a small circle by interchanging its winding and momentum modes. Patching a background by such dualities clearly goes beyond the notion of conventional geometry. However, there are extensive efforts to embed them into a framework called string geometry. It provides access to a vast number of new backgrounds with intriguing phenomenology, like e.g. the possibility to obtain de Sitter vacua. Double Field Theory (DFT) is the most promising approach to describe these backgrounds and their properties. But still, it is closely related to the torus. I will present a theory based on Closed String Field theory starting from a Wess-Zumino-Witten model which goes beyond the torus. It plays an important role in clarifying the recent confusion about different constraints in DFT. Furthermore it allows to uplift a large class of new backgrounds to string theory. These backgrounds are not T-dual to any geometric ones.

- 10:15 - 11:15: Chris Beasley (Northeastern University),
``Self-Linking for Legendrian Knots''

- 11th meeting: Fri-Sat April 4-5, joint UNC/Duke meeting following the
theme 'Mathieu moonshine'. Schedule:
- Thursday April 3: informal get-together around 6 pm in the evening at Hickory Tavern, beside lobby of Hampton Inn (370 East Main, Carrboro, just a few blocks from the physics dep't). People interested are welcome to join an informal dinner party.
- Friday April 4 at UNC: (see map)
- 9-10: snacks, outside Chapman 201
- 10-11 (Chapman 201): Daniel Persson (Sweden), ``Second quantization of Mathieu moonshine''
- 11-noon (Chapman 201): Daniel Whalen (Stanford), ``Vector-valued automorphic integrals''
- noon-1:45: lunch
- 1:45-2:45 (Chapman 201): Timm Wrase (Stanford), ``Mathieu moonshine and heterotic string compactifications''
- 2:45-4: break, possibly including tour of UNC campus's NC history museum
- 4-5: discussion in Chapman 125
- 6:30: dinner at Crook's Corner in Chapel Hill.

- Saturday April 5 at Duke:
- 10:15-11:15 (physics 119): Lara Anderson (VT), ``Geometric constraints in heterotic/F-theory duality''
- 11:30-1: lunch
- 1-2 (physics 119): Xi Dong (Stanford), ``String theory avatars of Conway and Mathieu symmetries''
- 2:15-3:15 (physics 119): Christoph Keller (Rutgers), ``Partition functions and Poincare series''
- 3:30-4:30 (physics 119): Ben Gaines (Duke), ``(0,2) deformations and the Hilbert scheme''

- 10th meeting: Friday October 11, 2013, in Gross Hall 330.
Schedule:
- 10:15-11:15: Sergei Gukov (Caltech), ``Fivebranes and 4-manifolds''
- 1-2: Eirik Svanes (Oxford), ``Heterotic supergravity, SU(3) structures, and the alpha' expansion''
- 2:15-3:15: Emanuel Scheidegger (Freiburg, Harvard), ``Topological strings and quasimodular forms''
- 3:30-4:30: Mauricio Romo (IPMU), ``Exact results in two-dimensional (2,2) supersymmetric gauge theories with boundary''

- 9th meeting: Saturday April 6, 2013, in Duke physics room 119.
Schedule:
- 10-11: Daniel Park (Stony Brook)
- 11:05-11:30: Bei Jia (VT)
- 1-2: Paul Aspinwall (Duke)
- 2:15-3:15: Nils Carqueville (Stony Brook)
- 3:30-4:30: Katrin Wendland (Freiburg)

- 8th meeting: Friday-Saturday September 28-29, 2012. Schedule:

Friday:- 10-11: Matt Ballard (Wisconsin) (Hudson Hall 218)
- noon-1: Nick Addington (Duke) (physics faculty lounge)

- 10:30-11:30: Callum Quigley (Chicago)
- 1-2: Marco Bertolini (Duke)
- 2:30-3:30: Djordje Minic (VT)

- 7th meeting: Saturday March 24, 2012, in the physics faculty lounge
(room 298).
Schedule:
- 10:30-11:30: Jacques Distler (Texas-Austin)
- 1-2: Ilarion Melnikov (Potsdam, AEI), ``Adventures in quantum restriction''
- 2:30-3:30: Katrin Becker (Texas A&M), ``D-brane and O-plane actions from string amplitudes,'' update: replaced by Daniel Robbins (Texas A&M)

- 6th meeting: Saturday October 8, 2011, in the physics first floor
classroom. Schedule:
- 10:30-11:30: Josh Lapan (Perimeter), ``Beyond CICY's through non-abelian GLSMs''
- 1:15-1:45: Bei Jia (VT), ``Rigidly supersymmetric gauge theories on curved superspace''
- 2-3: Philip Szepieowski (UVA), ``Consistent truncations of IIB on Sasaki-Einstein manifolds and N-2 supergravity in five dimensions''
- 3:15-4:15: Harry Thacker (UVA), ``The role of the RR U(1) guage field in holographic QCD''

- 5th meeting: Saturday April 2, 2011, in physics room 119.
Schedule:
- 10:30-11:30: Paul Aspinwall (Duke), ``New results from the ancient standard embedding''
- 1-2: Eric Sharpe (VT), ``Quantization of FI parameters in supergravity''
- 2:30-3:30: Djordje Minic (VT), ``String theory and non-equilibrium physics''

- 4th meeting: Saturday October 16, 2010, in physics 298 (faculty lounge).
Schedule:
- 10:30-11:30: Lara Anderson (U-Penn), ``Supersymmetry and moduli stabilization in heterotic theories''
- 1-2: Ronen Plesser (Duke)
- 2:30-3:30: Chaolun Wu (UVA), ``Relativistic and non-relativistic real-time finite-temperature AdS/CFT''

- 3rd meeting: Friday April 2, 2010, in physics 298 (faculty lounge).
Schedule:
- 10-11: Paul Aspinwall (Duke), ``Quivers and matrix factorizations''
- 11:15-12:15: Ronen Plesse (Duke)
- 2-3: Usama al-Binni (Tennessee), ``Hawking radiation and quasinormal modes for a black hole on a tensional codimension-2 brane''
- 3:20-4:20: Thomas Creutzig (UNC-CH)

- 2nd meeting: Friday October 2, 2009. Schedule:
- 10:15-11:15: James Alsup (Tennessee), ``Gravitational duals to time-dependent hydrodynamics'' (LSRC A156)
- 1-2: Diana Vaman (UVA), ``All 4-dimensional static, spherically symmetric, 2-charge abelian Kaluza-Klein black holes and their CFT duals'' (physics 298)
- 3:15-4:15: Stefano Guerra (Duke), ``The Catanese conjecture for flag varieties'' (physics 298)

- 1st meeting: Friday April 3, 2009, in LSRC A156. Schedule:
- 10:15-11:45: Paul Aspinwall (Duke), ``Geometry with zero-brane probes''
- 1:15-2:45: Lev Rozansky (UNC-CH)
- 2:45-4:15: Djordje Minic (VT), ``The physics of the Riemann zeros''