VT string theory seminars
This is the webpage for string theory seminars in the Virginia Tech physics department, held Wednesday afternoons 2:30 - 3:30 during the academic year.
Talk videos can be found on the Virginia Tech webpage (https://video.vt.edu/channel/VT%2BString%2BTheory%2BSeminar/343372102).
Spring 2025
• 02/26: Timo Weigand
- Title: Asymptotics in quantum gravity beyond geometry
- Abstract: The search for universal properties of effective field theories that derive from consistent quantum gravities is an important topic of current research. In this context, the Distance Conjecture and a refined version, the Emergent String Conjecture, predict the emergence of light towers of states towards the boundaries of moduli space in every consistent quantum gravity. If correct, this greatly constrains consistent gravitational effective theories in their parametrically weakly coupled regime. In compactifications of string or M-theory on Calabi-Yau varieties, these ideas have been verified explicitly by tracing them back to non-trivial properties of the underlying Calabi-Yau moduli spaces. Less clear, however, is under which conditions said asymptotic properties of a quantum gravity theory can be argued for without assuming a geometric origin via string or M-theory from the beginning. In this talk we analyse this question in the context of general five-dimensional supergravity theories with eight supercharges, focusing on infinite distance limits in the vector multiplet moduli space. With the help of brane probe arguments, we provide evidence that every consistent five-dimensional N=1 supergravity with a non-compact vector multiplet moduli space is either a compactification from six to five dimensions or a critical string theory. This result is obtained without any geometric or string theoretic input and lends non-trivial support to the Emergent String Conjecture.
- 03/12: Kai Xu
- 02/19: Edward Mazenc
- 03/26: Jim Halverson
- 04/02: Thomas Harvey
- 04/09: Rebecca Hicks
- 04/30: Elliott Gesteau
- 05/07: Magdalena Larfors
Fall 2024
- 09/04: Tom Rudelius
- Title: Taxonomy of Infinite-Distance Limits
- Abstract: The emergent string conjecture places tight constraints on the possible behavior of light towers in infinite-distance limits in quantum gravity moduli spaces (as required by the distance conjecture). In this talk, I show how these constraints can be understood as a sort of geometric "classification" on vertices, edges, and facets of a polytope, and I discuss the scope of this classification, some evidence for it, and some applications of it. If time permits, I will further discuss some related work involving a mysterious pattern in infinite-distance limits of moduli space and its persistence into the interior of 5d moduli spaces.
- Slides, video https://video.vt.edu/media/Tom+RudeliusA+Taxonomy+of+Infinite-Distance+Limits/1_ohbvcdkx/343372102
- 09/11: Bindusar Sahoo
- 09/18: Cyril Closset
- Title: Global structures of QFTs and elliptic curves: Reading between the sections
- Abstract: Thirty years ago, Seiberg and Witten famously solved the pure SU(2) super-Yang-Mills theory with N=2 supersymmetry in 4d. I will explore subtle aspects of this solution, motivated by simple questions such as: what is the difference between the SU(2) and the SO(3) gauge theory? The Seiberg-Witten (SW) solution is encoded by the SW geometry, which is a one-parameter family of elliptic curves. Less widely appreciated is the fact that global aspects of the strongly-coupled field theory, such as the difference between and SU(2) and SO(3) gauge group, are also encoded into the SW geometry, in particular in its Mordell-Weil group. After explaining this in detail, I may also discuss global aspects of 5d superconformal theories compactified on a circle.
- Slides, video https://video.vt.edu/media/Cyril+Closset%3A+Global+structures+of+QFTs+and+elliptic+curves%3A+Reading+between+the+sections/1_87a87i8v/343372102
- 09/25: Journal club on String field theory
- Title:
- Abstract:
- Slides, video
- 10/02: Justin Kulp
- Title: Twisted Tools for (Untwisted) Quantum Field Theory
- Abstract: One of the most important properties of QFTs is that they can be deformed by "turning on interactions." Essentially every observable can be viewed as coupling the theory to some external system. Famously, such interactions will (generically) break scale invariance, leading to familiar ideas of EFTs and RG flows in the space of QFTs. An underappreciated fact is that one can actually consider flows generated by any transformation, not just the usual scale transformations. In my talk, I will discuss a flow in the space of QFTs coming from (an analogue of) BRST symmetry. The beta-function for this "BRST-flow" controls deformations of the QFT and is highly mathematically constrained, generating a "homotopical" generalization of Lie algebras in any QFT, called L_\infty-algebras. These algebras are highly computable (requiring only a first course in QFT to compute) and contain familiar information such as anomalies and Operator Product Expansion coefficients. I will discuss how this formalism enables the systematic computation of BPS operators in supersymmetric QFTs (even if they are not "fully protected"), and describe the "holomorphic confinement" of N=1 SYM. Based on arXiv:2403.13049.
- Slides, video https://video.vt.edu/media/Justin+Kulp%3A+Twisted+Tools+for+%28Untwisted%29+Quantum+Field+Theory/1_btj58am7/343372102
- 10/09: Elia Mazzucchelli
- Title: The u(2|2)_1 WZW model
- Abstract: Recently a worldsheet description of string theory on AdS5 × S5 has been proposed, at the point in moduli space where the string theory is dual to free super Yang Mills. The worldsheet theory proposed involves a WZW model based on psu(2,2|4)_1 and reproduces the correct spectrum of free N = 4 SYM in 4D. However, its worldsheet theory exhibits a global psu(2, 2|4) + psu(2, 2|4) symmetry and the physical state condition must remove half of this symmetry. Therefore one may wonder if there exists a worldsheet theory description involving a smaller symmetry algebra. In this talk I present a candidate for this: the u(2|2)_1 WZW model. In particular, I’ll show the classification and construction of representations and modular invariants of u(2|2)_1. We are interested in discrete modular invariants, where the spectrum concentrates to the so called atypical sector and involves atypical modules.
- Slides, video https://video.vt.edu/media/Elia+Mazzucchelli%3A+The+u%282%7C2%29_1+WZW+model/1_gwr11vms/343372102
- 10/16: Herbert Clemens
- Title: A most-attractive del Pezzo surface over which to build Heterotic/F-theory duality in String Theory
- Abstract: In joint work with Stuart Raby we make the case that `most' of necessary input for Heterotic-F-theory duality in String Theory is already contained in a very particular choice of the del Pezzo base surface of the Heterotic model. Namely we choose B2 the complex projective CP2 plane blown up at 7 points having the full symmetry group of the cube and and in particular an involution with only four fixpoints. Tracking symmetry-breaking and constructing the crucial Higgs bundle turn out to be provided by beautiful properties of very classical algebraic geometry, with names like 'Cayley octad' and 'syzygetic tetrad of bitangents.’ These were already known to the algebraic geometers of the late 19th and early 20th century.The base B3 of the dual F-theory is elliptically fibered Calabi-Yau fourfold W4/B3 is simply B3=P1× B2 or, more precisely, the quotient B3∨ of B3 by an involution with finite fix-point set. The involution acts freely on the distinguished component 'SGUT' in B3 of the discriminant locus of the family W4/B3 of elliptic curves. This allows the symmetry of the 'Standard Model' to be achieved by a 'Wilson line' construction. A property of the model over SGUT∨ is that it has two points over which there is E8-symmetry. The local geometry 'near' these points can be easily tracked. This fact seems particularly relevant to Yukawa coupling calculations.
- Slides, video https://video.vt.edu/media/Herbert+Clemens%3A+A+most-attractive+del+Pezzo+surface+over+which+to+build+Heterotic+F-theory+duality+in+String+Theory/1_9kn6yfgw/343372102
- 10/23: Ho Tat Lam
- Title: Global Aspects of Exactly Marginal Current-Current Deformations
- Abstract: Conformal field theories connected by exactly marginal deformations form conformal manifolds. In two dimensions, a significant class of conformal manifolds is generated by bilinears of currents, known as current-current deformations. In this talk, we will revisit these deformations and prove that a dense set of points on the conformal manifolds are related to the seed theory through discrete gauging. This perspective allows us to connect the topology of the conformal manifolds with the anomalies of the currents and identify hidden non-invertible symmetries and conformal boundary conditions.
- Slides, video https://video.vt.edu/media/Ho+Tat+Lam%3A+Global+Aspects+of+Exactly+Marginal+Current-Current+Deformations/1_0lkmvdwi/343372102
- 10/30: Patrick Jefferson
- Title: EFT of Noncritical M-theory
- Abstract: Noncritical string theories in 2D are a tractable setting for exploring broad questions about string theory, such as the nature of its underlying degrees of freedom, the emergence of spacetime, and its landscape of solutions. It turns out that the dynamics of 2D string theory are related to an underlying noncritical version of M-theory, namely a double-scaled nonrelativistic 2+1D Fermi liquid, which has the potential to further illuminate many of these questions. However, this endeavor is complicated by the fact that, unlike 2D noncritical string theory, an effective 3D gravity description of noncritical M-theory has yet to be identified outside of very special limits of the theory. In this talk, I describe a new proposal for an EFT description of noncritical M-theory in terms of the shape dynamics of a 2+1D Fermi surface, and why this EFT represents a promising step towards obtaining a 3D gravity description. I will also describe some observables of our proposed EFT and their relationship to the physics of the underlying Fermi liquid, which serves as an important check of our proposal. Finally, I will comment on prospects for using this EFT to address various open questions about noncritical M-theory and, more generally, ten-dimensional superstring theory. Based on upcoming work with Tokiro Numasawa (University of Tokyo, Institute for Solid State Physics).
- Slides, video https://video.vt.edu/media/Patrick+Jefferson%3A+EFT+of+Noncritical+M-theory/1_ee0eyr5d/343372102
- 11/06: Minjae Cho
- Title: A (non-)worldsheet description of string backgrounds
- Abstract: For string backgrounds with known exact worldsheet theory descriptions, ordinary string perturbation theory can be employed to study their observables such as string spectrum and scattering. However, many of interesting string backgrounds, including AdS and flux compactifications, lack such descriptions, posing challenges in understanding their stringy physics. Since these backgrounds are typically described as solutions to low-energy supergravity theory, having a string-theoretic counterpart to this field theory is desirable. In this talk, we discuss how string field theory provides such a framework, along with its limitations. Despite such limitations, we illustrate its practical utility in examining physical observables, particularly in examples such as AdS and flux compactifications.
- Slides, video https://video.vt.edu/media/Minjae+Cho%3A+A+%28non-%29worldsheet+description+of+string+backgrounds/1_kpo4ryyb/343372102
- 11/13: Andrew Turner
- Title: Higgsing on SU(N) Symmetric Matter and its F-theory Realization
- Abstract: Higgsing on symmetric matter in an SU(N) gauge theory breaks to a special SO(N) subgroup with exotic matter representations. We discuss the explicit realization of such Higgsings in F-theory models and analyze the resulting models via dualities with heterotic and type IIB. The SO(N) gauge factors are supported on Kodaira type I_N singularities with nontrivial Tate monodromy. These models have nontrivial global gauge group quotients with no apparent Mordell–Weil torsion or additional U(1) factors. Similarly, we obtain a locally supported U(1) gauge factor without additional Mordell–Weil sections.
- Slides, video
- 12/04: Hamza Ahmed
- Title: A Twist on Heterotic Little String Dualities
- Abstract: 6D Little String Theories (LSTs) are an interesting class of UV complete theories which possess both QFT-like properties, such as higher-form global symmetries, and gravity-like properties, such as T-duality. In particular, this talk will focus on Heterotic LSTs and explore the T-duality landscape of such theories when discrete symmetry twists are allowed along the compactification circle. Starting from charge conjugation twists, we construct duality chains with (un)twisted LSTs by utilizing the duality invariant data and carefully considering the massive spectrum. This significantly extends the known T-duality landscape. To fully prove the duality, we realize dual theories as arising from inequivalent fibrations in F-theory on the same non-compact genus-one fibered Calabi-Yau (CY) manifold, and then use M/F-theory duality. Furthermore, we also consider discrete symmetries corresponding to the permutation of tensor multiplets and — based on the invariant data — construct a new class of duals (CHL-like twisted LSTs) with no known geometric construction.
- Slides, video https://video.vt.edu/media/Hamza+Ahmed%3A+A+Twist+on+Heterotic+Little+String+Dualities/1_mwf5cp3b/343372102
Spring 2024
- 02/14: Fabian Ruehle
- Title: Metric Flows
- Abstract: Recently, neural networks have been used to approximate Ricci-flat metrics of Calabi-Yau and G2 manifolds. In these setups, the neural network is the metric (in some choice of local coordinates). One typically starts from a reference metric that is not Ricci-flat and the optimization process induces a flow in metric space that ends at the Ricci-flat metric. We discuss this flow, how it compares to other metric flows such as Ricci flow, and implementations as well as numerical challenges.
- Slides, video https://video.vt.edu/media/Fabian+RuehleA+Metric+Flows/1_3097d6a1/343372102
- 02/21: Victor Rodriguez
- Title: The Virasoro Minimal String
- Abstract: I will introduce a new critical string theory in two dimensions and explain that this theory, viewed as two-dimensional quantum gravity on the worldsheet, is equivalent to a double-scaled matrix integral. The worldsheet theory consists of Liouville CFT coupled to timelike Liouville CFT. The double-scaled matrix integral has as its leading density of states the universal Cardy density of primaries in a two-dimensional CFT of central charge c, thus motivating the name Virasoro minimal string. The duality holds for any value of the continuous parameter c and reduces to the JT gravity/matrix integral duality in the large central charge limit, providing a precise stringy realization of JT gravity. From a target spacetime point of view, I will describe how this theory may be viewed as a cosmological background in two dimensions.
- Slides, video https://video.vt.edu/media/Victor+RodriguezA+The+Virasoro+Minimal+String/1_bqtsnvfb/343372102
- 02/28: Vahid Taghiloo
- Title: Fluid/p-form duality
- Abstract: In this talk, we demonstrate that an inviscid fluid in a near-equilibrium state, when viewed in the Lagrangian picture in d+1 spacetime dimensions, can be reformulated as a (d-1)-form gauge theory. We construct a fluid/gauge dictionary and show that volume-preserving diffeomorphisms on the fluid side manifest as a U(1) gauge symmetry on the (d-1)-form gauge theory side. Intriguingly, Kelvin’s circulation theorem and the mass continuity equation respectively appear as the Gauss law and the Bianchi identity on the gauge theory side. Furthermore, we show that at the level of the sources, the vortices in the fluid side correspond to the (d-2)-branes in the gauge theory side. We also consider fluid mechanics in the presence of boundaries and examine the boundary symmetries and corresponding charges from both the fluid and gauge theory perspectives.
- Slides, video https://video.vt.edu/media/Vahid+TaghilooA+Fluid+p-form+duality/1_p8otsshd/343372102
- 03/06: Ben Heidenreich
- Title: A Proof of the Weak Gravity Conjecture in Perturbative Bosonic String Theory
- Abstract: I present a complete proof of the Weak Gravity Conjecture (WGC) in perturbative, bosonic string theory, completing several partial arguments given in past literature. The proof leverages modular invariance, long-range forces, and their connection to extremal black holes. Along the way, I discuss several variants of the WGC that play a role in the proof. I conclude by previewing the extension of the proof to perturbative superstrings, which is work in progress.
- Slides, video https://video.vt.edu/media/Ben+HeidenreichA+A+Proof+of+the+Weak+Gravity+Conjecture+in+Perturbative+Bosonic+String+Theory/1_leeq1f5y/343372102
- 03/13: Chitraang Murdia
- Title: Normalization of Instantons in Minimal String Theory
- Abstract: We match instanton contributions between (2,p) minimal string theory and its dual matrix integral. The main technical insight is to use string field theory to analyze and cure the divergences in the cylinder diagram with both boundaries on a ZZ brane. This procedure gives a finite normalization constant for the non-perturbative effects in minimal string theory. We generalize these results to (p,q) minimal string theory and also to multi-instanton contributions.
- Slides, video https://video.vt.edu/media/Chitraang+MurdiaA+Normalization+of+Instantons+in+Minimal+String+Theory/1_ifw5841z/343372102
- 03/27: Thomas Grimm
- Title: Exact Flux Vacua and the Structure of the Landscape
- Abstract: The search for flux vacua that stabilize complex structure moduli in string compactifications poses a highly transcendental problem. This is due to the fact that geometric constraints dictate that the flux-induced scalar potentials necessarily contain exponential corrections. In this talk I discuss the landscape of exact flux vacua with vanishing superpotential for an F-theory compactification on a genuine Calabi-Yau fourfold. I show that along certain symmetry loci in moduli space the generically transcendental flux superpotential becomes algebraic and can be described using the periods of a surface. On such loci the vacua become dense when we do not bound the flux tadpole, while imposing the tadpole bound yields a small finite landscape of distinct vacua. These observations are deeply tied to the arithmetic structure underlying flux vacua. I will connect three topics: transcendentality/algebraicity of coupling functions, emergent symmetries, and the distribution of vacua. From a mathematical perspective, this is linked with the recent landmark results by Baldi, Klingler, and Ullmo about the Hodge locus that arose from connecting tame geometry and Hodge theory.
- Slides, video
- 04/03: Sahand Seifnashri
- Title: Anomalies and non-invertible symmetries on the lattice
- Abstract: We consider realizations of 't Hooft anomalies and non-invertible symmetries in 1+1d lattice Hamiltonian systems. In the case of invertible symmetries, we derive a simple formula for the 'anomaly cocycle' using topological defects and show it is the obstruction to gauging even on the lattice. Then, we study the exact non-invertible Kramers-Wannier symmetry of 1+1d lattice models on a tensor product Hilbert space of qubits. The non-invertible symmetry leads to a constraint similar to that of Lieb-Schultz-Mattis, implying that the system cannot have a unique gapped ground state. It is either in a gapless phase or in a gapped phase with three (or a multiple of three) ground states, associated with the spontaneous breaking of the lattice non-invertible symmetry.
- Slides, video https://video.vt.edu/media/Sahand+SeifnashriA+Anomalies+and+Non-invertible+Symmetries+on+the+Lattice/1_fis2g0lo/343372102
- 04/17: G. Joaquin Turiaci
- Title: Gravitational index of the heterotic string
- Abstract: Black holes with two charges in string theory are singular due to vanishing horizon area at extremality. Two seemingly contradictory resolutions are available in the literature. On one hand, it has been argued that higher-derivative effects create a string-sized extremal horizon. On the other hand, it has been argued that before such a small black hole even forms, there is a transition to a winding condensate and eventually a gas of strings. We show that, with some modifications, these two perspectives are compatible, but correspond to different observables.
- Slides, video https://video.vt.edu/media/G.+Joaquin+TuriaciA+Gravitational+index+of+the+heterotic+string/1_0ca099zm/343372102
- 05/01: Andrea E. V. Ferrari
- Title: Berry Connections for 2d (2,2) Theories and (Generalised) Cohomology Theories
- Abstract: It has long been known that supersymmetric (SUSY) ground states of QFTs that flow to a sigma-model are closely related to certain cohomology theories of the target. A more recent observation is that 3d SUSY QFTs quantised on an elliptic curve can be endowed with Berry connections, whose structure is able to capture the equivariant elliptic cohomology of the Higgs branch. I will present the first results of an ongoing effort to relate more broadly the structure of Berry connections of SUSY QFTs to various kinds of (generalised) cohomology theories. Focusing on 2d (2,2) models, whose Berry connections are generalised periodic monopoles, I will sketch how one kind of spectral data (difference modules) is related to novel difference equations for brane amplitudes and hemisphere partition functions. These difference equations are quantisations of spectral varieties that are related to the equivariant quantum cohomology of the target. I will moreover briefly mention how another kind of spectral data (vector bundles with filtrations) is instead related to its equivariant quantum K-theory. These aspects fit into a rich web of relations between various topics in mathematics.
- Slides, video https://video.vt.edu/media/Andrea+E.+V.+FerrariA+Berry+Connections+for+2d+%282%2C2%29+Theories+and+%28Generalised%29+Cohomology+Theories/1_ny4q7gmo/343372102
- 05/08: Francesco Benini
- Title: Anomalies and Gauging of U(1) Symmetries
- Abstract: The Symmetry TFT of a quantum field theory is a Topological Field Theory in one dimension more, that describes the structure of the symmetry, its representations, its anomalies, and the possible topological manipulations (gaugings). Until recently only the case of finite symmetries had been addressed. I will present a proposal for the Symmetry TFT of theories with a U(1) symmetry: it is a BF theory with a continuum of topological operators. I will discuss many examples, including chiral anomalies, 2-groups, the non-invertible Q/Z chiral symmetry in 4d with ABJ anomaly, and I will provide a few features of the non-Abelian case.
- Slides, video https://video.vt.edu/media/Francesco+BeniniA+Anomalies+and+Gauging+of+U%281%29+Symmetries/1_vldfo2pu/343372102