1 December 2019 Newton–Okounkov bodies, cluster duality, and mirror symmetry for Grassmannians
K. Rietsch, L. Williams
Duke Math. J. 168(18): 3437-3527 (1 December 2019). DOI: 10.1215/00127094-2019-0028


In this article we use cluster structures and mirror symmetry to explicitly describe a natural class of Newton–Okounkov bodies for Grassmannians. We consider the Grassmannian X=Grnk(Cn), as well as the mirror dual Landau–Ginzburg model (Xˇ,W:XˇC), where Xˇ is the complement of a particular anticanonical divisor in a Langlands dual Grassmannian Xˇ=Grk((Cn)) and the superpotential W has a simple expression in terms of Plücker coordinates. Grassmannians simultaneously have the structure of an A-cluster variety and an X-cluster variety; roughly speaking, a cluster variety is obtained by gluing together a collection of tori along birational maps. Given a plabic graph or, more generally, a cluster seed G, we consider two associated coordinate systems: a network or X-cluster chart ΦG:(C)k(nk)X and a Plücker cluster or A-cluster chart ΦG:(C)k(nk)Xˇ. Here X and Xˇ are the open positroid varieties in X and Xˇ, respectively. To each X-cluster chart ΦG and ample boundary divisor D in XX, we associate a Newton–Okounkov body ΔG(D) in Rk(nk), which is defined as the convex hull of rational points; these points are obtained from the multidegrees of leading terms of the Laurent polynomials ΦG(f) for f on X with poles bounded by some multiple of D. On the other hand, using the A-cluster chart ΦG on the mirror side, we obtain a set of rational polytopes—described in terms of inequalities—by writing the superpotential W as a Laurent polynomial in the A-cluster coordinates and then tropicalizing. Our first main result is that the Newton–Okounkov bodies ΔG(D) and the polytopes obtained by tropicalization on the mirror side coincide. As an application, we construct degenerations of the Grassmannian to normal toric varieties corresponding to (dilates of ) these Newton–Okounkov bodies. Our second main result is an explicit combinatorial formula in terms of Young diagrams, for the lattice points of the Newton–Okounkov bodies, in the case in which the cluster seed G corresponds to a plabic graph. This formula has an interpretation in terms of the quantum Schubert calculus of Grassmannians.


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K. Rietsch. L. Williams. "Newton–Okounkov bodies, cluster duality, and mirror symmetry for Grassmannians." Duke Math. J. 168 (18) 3437 - 3527, 1 December 2019. https://doi.org/10.1215/00127094-2019-0028


Received: 22 May 2018; Revised: 11 March 2019; Published: 1 December 2019
First available in Project Euclid: 11 November 2019

zbMATH: 07174392
MathSciNet: MR4034891
Digital Object Identifier: 10.1215/00127094-2019-0028

Primary: 14M15
Secondary: 13F60 , 14J33 , 52B20

Keywords: cluster algebra , Grassmannians , mirror symmetry , Newton–Okounkov bodies

Rights: Copyright © 2019 Duke University Press


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Vol.168 • No. 18 • 1 December 2019
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