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Register a new userGushel-Mukai varieties: linear spaces and periods
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Beauville and Donagi proved in 1985 that the primitive middle cohomology of a smooth complex cubic fourfold and the primitive second cohomology of its variety of lines, a smooth hyperkahler fourfold, are isomorphic as polarized integral Hodge structures. We prove analogous statements for smooth complex Gushel-Mukai varieties of dimension 4 (resp. 6), i.e., smooth dimensionally transverse intersections of the cone over the Grassmannian Gr(2,5), a quadric, and two hyperplanes (resp. of the cone over Gr(2,5) and a quadric). The associated hyperkahler fourfold is in both cases a smooth double cover of a hypersurface in ${bf P}^5$ called an EPW sextic.
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We describe the moduli stack of Gushel-Mukai varieties as a global quotient stack and its coarse moduli space as the corresponding GIT quotient. The construction is based on a comprehensive study of the relation between this stack and the stack of Lagrangian data; roughly speaking, we show that the former is a generalized root stack of the latter. As an application, we define the period map for Gushel-Mukai varieties and construct some complete nonisotrivial families of smooth Gushel-Mukai varieties. In an appendix, we describe a generalization of the root stack construction used in our approach to the moduli space.
We provide a stable rationality construction for some smooth complex Gushel-Mukai varieties of dimension 6. As a consequence, we compute the integral singular cohomology of any smooth Gushel-Mukai sixfold and in particular, show that it is torsion-free.
The Kuznetsov component $mathcal{K}u(X)$ of a Gushel--Mukai (GM) threefold has two numerical $(-1)$-classes with respect to the Euler form. We describe the Bridgeland moduli spaces for stability conditions on Kuznetsov components with respect to each of the $(-1)$-classes and prove refined and birational categorical Torelli theorems in terms of $mathcal{K}u(X)$. We also prove a categorical Torelli theorem for special GM threefolds. We study the smoothness and singularities on Bridgeland moduli spaces for all smooth GM threefolds and use this to prove a conjecture of Kuznetsov--Perry in dimension three under a mild assumption. Finally, we use our moduli spaces to restate a conjecture of Debarre--Iliev--Manivel regarding fibers of the period map for ordinary GM threefolds. We also prove the restatement of this conjecture infinitesimally using Hochschild (co)homology.
Over complex numbers, the Fourier-Mukai partners of abelian varieties are well-understood. A celebrated result is Orlovs derived Torelli theorem. In this note, we study the FM-partners of abelian varieties in positive characteristic. We notice that, in odd characteristics, two abelian varieties of odd dimension are derived equivalent if their associated Kummer stacks are derived equivalent, which is Krug and Sosnas result over complex numbers. For abelian surfaces in odd characteristic, we show that two abelian surfaces are derived equivalent if and only if their associated Kummer surfaces are isomorphic. This extends the result [doi:10.1215/s0012-7094-03-12036-0] to odd characteristic fields, which solved a classical problem originally from Shioda. Furthermore, we establish the derived Torelli theorem for supersingular abelian varieties and apply it to characterize the quasi-liftable birational models of supersingular generalized Kummer varieties.
We study quantum geometry of Nakajima quiver varieties of two different types - framed A-type quivers and ADHM quivers. While these spaces look completely different we find a surprising connection between equivariant K-theories thereof with a nontrivial match between their equivariant parameters. In particular, we demonstrate that quantum equivariant K-theory of $A_n$ quiver varieties in a certain $ntoinfty$ limit reproduces equivariant K-theory of the Hilbert scheme of points on $mathbb{C}^2$. We analyze the correspondence from the point of view of enumerative geometry, representation theory and integrable systems. We also propose a conjecture which relates spectra of quantum multiplication operators in K-theory of the ADHM moduli spaces with the solution of the elliptic Ruijsenaars-Schneider model.
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