arXiv subjects

Ahsan Z. Khan

Publications and source records attributed to Ahsan Z. Khan.

7 recordsLinked to original sources

arXiv2026

Poisson Vertex Algebra of Seiberg-Witten Theory

The space of local operators in the $Q$-cohomology of the holomorphic-topological supercharge in a four-dimensional $\mathcal{N}=2$ theory carries the structure of a Poisson vertex algebra. This note studies the Poisson vertex algebra associated to the pure $\mathcal{N}=2$ gauge theory with gauge group $SU(2)$. We propose an explicit Poisson vertex algebra $A$, claimed to be isomorphic to the algebra of holomorphic-topological observables to all orders in perturbation theory. We compute the Hilbert-Poincaré series of $A$ and show that it refines the Schur index of the pure $SU(2)$ theory. We show that $A$ admits a further differential $Q_{\text{inst}}$ which we hypothesize captures non-perturbative corrections, and compute the cohomology of this differential. We thus present an explicit candidate for the space of non-perturbative holomorphic-topological observables of Seiberg-Witten theory.

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arXiv2025

Poisson Vertex Algebras and Three-Dimensional Gauge Theory

We introduce a mixed holomorphic-topological gauge theory in three dimensions associated to a (freely generated) Poisson vertex algebra. The $λ$-bracket of the PVA plays the role of the structure constants of the gauge algebra and the gauge invariance of the theory holds if and only if the $λ$-bracket Jacobi identity is satisfied. We show that the holomorphic-topological symmetry of the theory enhances to full topological symmetry if the Poisson vertex algebra contains a Virasoro element. We outline examples associated to PVAs of $\mathcal{W}$-type and demonstrate their connections to various versions of $3d$ gravity. We expect the three-dimensional Poisson sigma model to play an important role in the deformation quantization of Poisson vertex algebras.

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arXiv2024

On the Algebra of the Infrared with Twisted Masses

The Algebra of the Infrared \cite{Gaiotto:2015aoa} is a framework to construct local observables, interfaces, and categories of supersymmetric boundary conditions of massive $\mathcal{N}=(2,2)$ theories in two dimensions by using information only about the BPS sector. The resulting framework is known as the ``web-based formalism.'' In this paper we initiate the generalization of the web-based formalism to include a much wider class of $\mathcal{N}=(2,2)$ quantum field theories than was discussed in \cite{Gaiotto:2015aoa}: theories with non-trivial twisted masses. The essential new ingredient is the presence of BPS particles within a fixed vacuum sector. In this paper we work out the web-based formalism for the simplest class of theories that allow for such BPS particles: theories with a single vacuum and a single twisted mass. We show that even in this simple setting there are interesting new phenomenon including the emergence of Fock spaces of closed solitons and a natural appearance of Koszul dual algebras. Mathematically, studying theories with twisted masses includes studying the Fukaya-Seidel category of A-type boundary conditions for Landau-Ginzburg models defined by a closed holomorphic one-form. This paper sketches a web-based construction for the category of A-type boundary conditions for one-forms with a single Morse zero and a single non-trivial period. We demonstrate our formalism explicitly in a particularly instructive example.

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arXiv2023

On the $A_{\infty}$-Category of a Holomorphic Moment Map

Let $M$ be a hyperKähler manifold equipped with a $U(1)$ hyperKähler isometry, and let $I$ be a complex structure on $M$. In this note, we study the $A_{\infty}$-category of A-branes for the Landau-Ginzburg model with target space $(M,I)$, and superpotential being the $I$-holomorphic moment map. We show that if $I$ is a generic complex structure, the $A_{\infty}$-category is semi-simple. For exceptional complex structures, though typically not semi-simple, the category still has no instanton corrections. We illustrate the $A_{\infty}$-category at both generic and exceptional loci when $M$ is the cotangent bundle of the projective line.

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arXiv2022

Holomorphic Surface Defects in Four-Dimensional Chern-Simons Theory

We derive the framing anomaly of four-dimensional holomorphic-topological Chern-Simons theory formulated on the product of a topological surface and the complex plane. We show that the presence of this anomaly allows one to couple four-dimensional Chern-Simons theory to holomorphic field theories with Kac-Moody symmetry, where the Kac-Moody level $k$ is critical $k=-h^{\vee}$. Applying this result to a holomorphic sigma model into a complex coadjoint orbit, we derive that four-dimensional Chern-Simons theory admits holomorphic monodromy defects.

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arXiv2020

Categorical Wall-Crossing in Landau-Ginzburg Models

We describe how categorical BPS data including chain complexes of solitons, CPT pairings, and interior amplitudes jump across a wall of marginal stability in two-dimensional $\mathcal{N}=(2,2)$ models. We show that our jump formulas hold if and only if the $A_{\infty}$-categories of half-BPS branes constructed on either side of the wall are homotopy equivalent. These results can be viewed as categorical enhancements of the Cecotti-Vafa wall-crossing formula.

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arXiv2015

Topological Field Theory Amplitudes for $A_{N-1}$ Fibration

We study the partition function ${\cal N}=1$ 5D $U(N)$ gauge theory with $g$ adjoint hypermultiplets and show that for massless adjoint hypermultiplets it is equal to the partition function of a two dimensional topological field on a genus $g$ Riemann surface. We describe the topological field theory by its amplitudes associated with cap, propagator and pair of pants. These basic amplitudes are open topological string amplitudes associated with certain Calabi-Yau threefolds in the presence of Lagrangian branes.

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