Invariants of finite group schemes

Numerical invariants of Fano schemes of linear subspaces on complete intersections

The goal of this paper is to explore the genus and degree of the Fano scheme of linear subspaces on a complete intersection in a complex projective space. Firstly, suppose that the expected dimension of the Fano scheme is one, we prove a genus-degree formula. Secondly, we give a degree formula for the Fano scheme.

通过商方案研究量子K不变量 I

Quantum $K$-invariants via Quot schemes I

本文通过商方案和拓扑量子场论方法，研究Grassmannian的量子K不变量，并推导出其小量子K环的表达式。

Donaldson-Thomas invariants, linear systems and punctual Hilbert schemes

We study certain DT invariants arising from stable coherent sheaves in a nonsingular projective threefold supported on the members of a linear system of a fixed line bundle. When the canonical bundle of the threefold satisfies certain positivity conditions, we relate the DT invariants to Carlsson-Okounkov formulas for the "twisted Euler's number" of the punctual Hilbert schemes of nonsingular surfaces, and conclude they have a modular property.

Gopakumar-Vafa BPS invariants, Hilbert schemes and quasimodular forms. I

We prove a closed formula for leading Gopakumar- Vafa BPS invariants of local Calabi-Yau geometries given by the canonical line bundles of toric Fano surfaces. It shares some similar features with Goettsche-Yau-Zaslow formula: Connection with Hilbert schemes, connection with quasimodular forms, and quadratic property after suitable transformation. In Part I of this paper we will present the case of projective plane, more general cases will be presented in Part II.

Comparison theorems for deformation functors via invariant theory

We compare deformations of algebras to deformations of schemes in the setting of invariant theory. Our results generalize comparison theorems of Schlessinger and the second author for projective schemes. We consider deformations (abstract and embedded) of a scheme $X$ which is a good quotient of a quasi-affine scheme $X^\prime$ by a linearly reductive group $G$ and compare them to invariant deformations of an affine $G$-scheme containing $X^\prime$ as an open invariant subset. The main theorems give conditions for when the comparison morphisms are smooth or isomorphisms.

Unipotent invariants of filtered representations of quivers and the isospectral Hilbert scheme

Given any finite quiver, we consider a complete flag of vector spaces over each vertex. Consider the unipotent invariant subalgebra of the coordinate ring of the filtered quiver representation subspace. We prove that the dimension of the algebraic variety of the unipotent invariant subalgebra is finite. We also construct an ADHM analog for the Borel subalgebra setting, showing its birationality to the isospectral Hilbert scheme. Quiver-graded Steinberg varieties, quantum Hamiltonian reduction, and deformation quantization constructions for the nonreductive setting are discussed, ending with op…

Parabolic semi-orthogonal decompositions and Kummer flat invariants of log schemes

We construct semi-orthogonal decompositions on triangulated categories of parabolic sheaves on certain kinds of logarithmic schemes. This provides a categorification of the decomposition theorems in Kummer flat K-theory due to Hagihara and Nizioł. Our techniques allow us to generalize Hagihara and Nizioł's results to a much larger class of invariants in addition to K-theory, and also to extend them to more general logarithmic stacks.

三维曲面上点的Quot概形的虚拟不变量

Virtual invariants of Quot schemes of points on threefolds

该研究在光滑射影三维曲面的零维商Quot概形上构造虚拟维数为零的殆完全阻碍理论以定义虚拟不变量，通过配边、退化、环面局部化等方法计算并证明了Ricolfi猜想。

可对角化幺半群概形自作用的代数磁不变量

Algebraic Magnetism Invariants of Self-Actions of Diagonalizable Monoid Schemes

该研究提出一种计算可对角化幺半群概形自作用纯磁体的方法，通过锐幺半群极小生成元描述，且代数磁学能检测幺半群模可逆元后的锐性与极小生成元。

Invariant Hilbert scheme resolution of Popov's $SL(2)$-varieties II: the non-toric case

This article is a continuation of [Kub18], which proves that if a $3$-dimensional affine normal quasihomogeneous $SL(2)$-variety $E$ is toric, then it has an equivariant resolution of singularities given by an invariant Hilbert scheme $\mathcal H$. In this article, we consider the case where $E$ is non-toric and show that the Hilbert-Chow morphism $γ: \mathcal H \to E$ is a resolution of singularities and that $\mathcal H$ is isomorphic to the minimal resolution of a weighted blow-up of $E$.

Gromov-Witten theory of schemes in mixed characteristic

We define Gromov-Witten classes and invariants of smooth projective schemes of finite presentation over a Dedekind domain. We prove that they are deformation invariants and verify the fundamental axioms. For a smooth projective scheme over a Dedekind domain, we prove that the invariants of fibers in different characteristics are the same. We show that genus zero Gromov-Witten invariants define a potential which satisfies the WDVV equation and we deduce from this a reconstruction theorem for genus zero Gromov-Witten invariants in arbitrary characteristic.

曲线上商概型的乔伊斯不变量与Virasoro约束

Joyce's invariant and Virasoro Constraints for Quot schemes on curves

该研究为曲线上的商概型引入乔伊斯枚举不变量，结合顶点代数框架证明其Virasoro约束，并用于计算商概型上$f$-类的虚相交数。

An example of an Sl_2-Hilbert scheme with multiplicities

We determine the invariant Hilbert scheme of the zero fibre of the moment map of an action of Sl_2 on (C^2)^6 as one of the first examples of invariant Hilbert schemes with multiplicities. While doing this, we present a general procedure how to realise the calculation of invariant Hilbert schemes, which have been introduced by Alexeev and Brion. We also consider questions of smoothness and connectedness and thereby show that our Hilbert scheme gives a resolution of singularities of the symplectic reduction of the action.

非交换概形Morita不变量的Künneth定理与扩张定理

Künneth and extension theorems for Morita invariants of non-commutative schemes

本文运用dg-范畴的导出Morita理论，将结合dg-代数的Morita不变量恒等式有效域拓展至非交换概形，给出其底层代数捕获Morita不变性质的简洁阐释，并应用Künneth公式分解拟幻影范畴乘积的Hochschild上同调，为dg-模体系提供统一视角。

Two point extremal Gromov-Witten invariants of Hilbert schemes of points on surfaces

Given an algebraic surface $X$, the Hilbert scheme $X^{[n]}$ of $n$-points on $X$ admits a contraction morphism to the $n$-fold symmetric product $X^{(n)}$ with the extremal ray generated by a class $β_n$ of a rational curve. We determine the two point extremal GW-invariants of $X^{[n]}$ with respect to the class $dβ_n$ for a simply-connected projective surface $X$ and the quantum first Chern class operator of the tautological bundle on $X^{[n]}$. The methods used are vertex algebraic description of $H^*(X^{[n]})$, the localization technique applied to $X=\mathbb P^2$, and a generalization of …

Quot schemes, Segre invariants, and inflectional loci of scrolls over curves

Let $E$ be a vector bundle over a smooth curve $C$, and $S = \mathbb{P} E$ the associated projective bundle. We describe the inflectional loci of certain projective models $ψ\colon S \dashrightarrow \mathbb{P}^n$ in terms of Quot schemes of $E$. This gives a geometric characterisation of the Segre invariant $s_1 (E)$, which leads to new geometric criteria for semistability and cohomological stability of bundles over $C$. We also use these ideas to show that for general enough $S$ and $ψ$, the inflectional loci are all of the expected dimension. An auxiliary result, valid for a general subvarie…

Good degeneration of Quot-schemes and coherent systems

We construct good degenerations of Quot-schemes and coherent systems using the stack of expanded degenerations. We show that these good degenerations are separated and proper DM stacks of finite type. Applying to the projective threefolds, we derive degeneration formulas for DT-invariants of ideal sheaves and PT stable pair invariants.

On Milnor classes via invariants of singular subschemes

We derive a formula for the Milnor class of scheme-theoretic global complete intersections (with arbitrary singularities) in a smooth variety in terms of the Segre class of its singular scheme. In codimension one the formula recovers a formula of Aluffi for the Milnor class of a hypersurface.

Quot schemes for flags and Gromov invariants for flag varieties

Using Quot schemes and a localization theorem we study Gromov-Witten invariants for partial flag varieties. The strategy is to extend A. Bertram's result of Gromov-Witten invariants for special Schubert varieties of Grassmannians to the case of partial flag varieties. To do so a Grothendieck's Quot scheme is generalized for flags and proven to be an irreducible, rational, smooth, projective variety following Strømme \cite{St}.

Invariant Hilbert schemes and Wonderful varieties

The invariant Hilbert schemes considered in \cite{BC1} were proved to be affine spaces. The proof relied on the classification of strict wonderful varieties. We obtain in the present article a classification-free proof of the affinity of these invariant Hilbert scheme by means of deformation theoretical arguments. As a consequence we recover in a shorter way the classification of strict wonderful varieties. This provides an alternative and new approach to answer Luna's conjecture.

Relations for virtual fundamental classes of Hilbert schemes of curves on surfaces

In [DKO] we constructed virtual fundamental classes $[[ Hilb^m_V ]]$ for Hilbert schemes of divisors of topological type m on a surface V, and used these classes to define the Poincare invariant of V: (P^+_V,P^-_V): H^2(V,Z) --> Λ^* H^1(V,Z) x Λ^* H^1(V,Z) We conjecture that this invariant coincides with the full Seiberg-Witten invariant computed with respect to the canonical orientation data. In this note we prove that the existence of an integral curve $C \subset V$ induces relations between some of these virtual fundamental classes $[[Hilb^m_V ]]$. The corresponding relations for the Poinca…

Quotients and invariants of AS-sets equipped with a finite group action

Using the geometric quotient of a real algebraic set by the action of a finite group G, we construct invariants of GAS sets with respect to equivariant homeomorphisms with AS-graph, including additive invariants with values in Z.

Generators of invariant linear system on tropical curves for finite isometry group

For a tropical curve and a finite subgroup of the isometry group of the tropical curve, we prove, extending the work by Haase, Musiker and Yu, that the invariant part of the complete linear system associated to a invariant effective divisor on the tropical curve is finitely generated.

区分代数空间与概形

Distinguishing Algebraic Spaces from Schemes

本文引入代数空间与叠的局部不变量，提出拓扑判据判断叠的模空间是否为概形，并应用于光滑射影曲线上主丛的模空间研究。

Phylogenetic invariants for $\mathbb{Z}_3$ scheme-theoretically

We study phylogenetic invariants of models of evolution whose group of symmetries is the cyclic group with 3 elements. We prove that projective schemes corresponding to the ideal I of phylogenetic invariants of such a model and to its subideal I' generated by elements of degree at most 3 are the same. This is motivated by a conjecture of Sturmfels and Sullivant, which would imply that I = I'.

The invariant Quot scheme

Given an affine scheme X with an action of a reductive group G and a G-linearized coherent sheaf M, we construct the ``invariant Quot scheme'' that parametrizes the quotients of M whose space of global sections is a direct sum of simple G-modules with fixed finite multiplicities. Then we determine the invariant Quot scheme in a simple situation, where X is the cone of primitive vectors of a simple G-module and M is the free sheaf on X generated by another simple G-module. This invariant Quot scheme has only one point, that is reduced in most of the cases. The only cases where it is not reduced…

Cohomological invariants of finite Coxeter groups

In this paper, we generalize Serre's splitting theorem for cohomological invariants of the symmetric group to finite Coxeter groups, provided that the ground field has characteristic zero. We then use this principle to determine all the cohomological invariants of Weyl groups of classical type with coefficients modulo 2.

Invariant theory for the commuting scheme of symplectic Lie algebras

We prove the Chevalley restriction theorem for the commuting scheme of symplectic Lie algebras. The key step is the construction of the inverse map of the Chevalley restriction map called the spectral data map. Along the way, we establish a certain multiplicative property of the Pfaffian which is of independent interest.

Invariants of noncommutative projective schemes

In this note we compute several invariants (e.g. algebraic K-theory, cyclic homology and topological Hochschild homology) of the noncommutative projective schemes associated to Koszul algebras of finite global dimension.

半稳定分解与群方案作用于射影方案的不变量的最小性

Semistable reductions and minimalities of invariants for group scheme actions on projective schemes

研究群方案作用于射影方案的半稳定分解与不变量最小性，建立关键定位区域的重合与非空性，拓展了动态系统中的高维结果。

不变量理论中的模概形

Module schemes in invariant theory

本文通过商模概形（至多相差修正）替代共变模，将Auslander在二维小作用下的表示与极大Cohen-Macaulay模对应推广到所有线性作用。

有重叠群作用的仿射方案不变变形理论

Invariant deformation theory of affine schemes with reductive group action

本文提出了一种计算具有重叠群作用的仿射方案不变变形的算法，并应用该方法确定了新的不变Hilbert方案例子及其奇点特性。

Descente par éclatements en K-théorie invariante par homotopie

These notes give a proof of the representability of homotopy invariant K-theory in the stable homotopy category of schemes (which was announced by Voevodsky). One deduces from the proper base change theorem in stable homotopy theory of schemes a descent by blow-ups theorem for homotopy invariant K-theory.

概形的$\mathbb{A}^1$-不变动机上同调

$\mathbb{A}^1$-invariant motivic cohomology of schemes

本文在任意拟紧拟分离概形上实现了Voevodsky的$\mathbb{A}^1$-不变动机上同调纲领，引入了通过Atiyah--Hirzebruch谱序列与同伦$K$-理论关联的理论，并证明了切片相关猜想。

Refined knot invariants and Hilbert schemes

We consider the construction of refined Chern-Simons torus knot invariants by M. Aganagic and S. Shakirov from the DAHA viewpoint of I. Cherednik. We give a proof of Cherednik's conjecture on the stabilization of superpolynomials, and then use the results of O. Schiffmann and E. Vasserot to relate knot invariants to the Hilbert scheme of points on the plane. Then we use the methods of the second author to compute these invariants explicitly in the uncolored case. We also propose a conjecture relating these constructions to the rational Cherednik algebra, as in the work of the first author, A. …

Invariants de classes : propriétés fonctorielles et applications à l'étude du noyau

The class-invariant homomorphism allows one to measure the Galois module structure of torsors--under a finite flat group scheme--which lie in the image of a coboundary map associated to an exact sequence. It has been introduced first by Martin Taylor (the exact sequence being given by an isogeny between abelian schemes). We begin by giving general properties of this homomorphism, then we pursue its study in the case when the exact sequence is given by the multiplication by $n$ on an extension of an abelian scheme by a torus.

Finite phylogenetic complexity of $Z_p$ and invariants for $Z_3$

We study phylogenetic complexity of finite abelian groups - an invariant introduced by Sturmfels and Sullivant. The invariant is hard to compute - so far it was only known for $Z_2$, in which case it equals $2$. We prove that phylogenetic complexity of any group $Z_p$, where $p$ is prime, is finite. We also show, as conjectured by Sturmfels and Sullivant, that the phylogenetic complexity of $Z_3$ equals $3$.

The classifying topos of a group scheme and invariants of symmetric bundles

Let $Y$ be a scheme in which 2 is invertible and let $V$ be a rank $n$ vector bundle on $Y$ endowed with a non-degenerate symmetric bilinear form $q$. The orthogonal group ${\bf O}(q)$ of the form $q$ is a group scheme over $Y$ whose cohomology ring $H^*(B_{{\bf O}(q)},{\bf Z}/2{\bf Z})\simeq A_Y[HW_1(q),..., HW_n(q)]$ is a polynomial algebra over the étale cohomology ring $A_Y:=H^*(Y_{et},{\bf Z}/2{\bf Z})$ of the scheme $Y$. Here the $HW_i(q)$'s are Jardine's universal Hasse-Witt invariants and $B_{{\bf O}(q)}$ is the classifying topos of ${\bf O}(q)$ as defined by Grothendieck and Giraud. T…

Finite u Invariant and Bounds on Cohomology Symbol Lengths

In this note we answer a question of Parimala's, showing that fields with finite $u$ invariant have bounds on the symbol lengths in their $μ_2$ cohomology in all degrees.

The Ekedahl Invariants for finite groups

In 2009 Ekedahl introduced certain cohomological invariants of finite groups which are naturally related to the Noether Problem. We show that these invariants are trivial for every finite group in GL_3(k) and for the fifth discrete Heisenberg group H_5. Moreover in the case of finite linear groups with abelian projective reduction, these invariants satisfy a recurrence relation in a certain Grothendieck group for abelian groups.

Twisted modules and co-invariants for commutative vertex algebras of jet schemes

Let $Z \subset \mathbb{A}^k$ be an affine scheme over $\C$ and $\J Z$ its jet scheme. It is well-known that $\mathbb{C}[\J Z]$, the coordinate ring of $\J Z$, has the structure of a commutative vertex algebra. This paper develops the orbifold theory for $\mathbb{C}[\J Z]$. A finite-order linear automorphism $g$ of $Z$ acts by vertex algebra automorphisms on $\mathbb{C}[\J Z]$. We show that $\mathbb{C}[\J^g Z]$, where $\J^g Z$ is the scheme of $g$--twisted jets has the structure of a $g$-twisted $\mathbb{C}[\J Z]$ module. We consider spaces of orbifold coinvariants valued in the modules $\mathb…

Modified mixed realizations, new additive invariants, and periods of dg categories

To every scheme, not necessarily smooth neither proper, we can associate its different mixed realizations (de Rham, Betti, etale, Hodge, etc) as well as its ring of periods. In this note, following an insight of Kontsevich, we prove that, after suitable modifications, these classical constructions can be extended from schemes to the broad setting of dg categories. This leads to new additive invariants, which we compute in the case of differential operators, as well as to a theory of periods of dg categories. Among other applications, we prove that the ring of periods of a scheme is invariant u…