Appendix to "The Chow rings of generalized Grassmannians"

Chow quotients of Grassmannians by diagonal subtori

The literature on maximal torus orbits in the Grassmannian is vast; in this paper we initiate a program to extend this to diagonal subtori. Our main focus is generalizing portions of Kapranov's seminal work on Chow quotient compactifications of these orbit spaces. This leads naturally to discrete polymatroids, generalizing the matroidal framework underlying Kapranov's results. By generalizing the Gelfand-MacPherson isomorphism, these Chow quotients are seen to compactify spaces of arrangements of parameterized linear subspaces, and a generalized Gale duality holds here. A special case is birat…

The Chow Ring of the Non-Linear Grassmannian

Let M_{P^k}(P^r, d) be the moduli space of unparameterized maps μ:P^k -> P^r satisfying μ^*(O(1))= O(d). M_{P^k}(P^r,d) is a quasi-projective variety, and, in case k=1, M_{P^1}(P^r,d) is the fundamental open cell of Kontsevich's space of stable maps \bar{M}_{0,0}(P^r,d). It is shown that the Q-coefficient Chow ring of M_{P^k}(P^r,d) is canonically isomorphic to the Chow ring of the Grassmannian Gr(P^k, P^r)= M_{P^k}(P^r,1).

Chow quotients of Grassmannian I

We introduce a certain compactification of the space of projective configurations i.e. orbits of the group $PGL(k)$ on the space of $n$ - tuples of points in $P^{k-1}$ in general position. This compactification differs considerably from Mumford's geometric invariant theory quotient. It is obtained by considering limit position (in the Chow variety) of the closures of generic orbits. The same result will be obtained if we study orbits of the maximal torus on the Grassmannian $G(k,n)$. We study in detail the closures of the torus orbits and their "visible contours" which are Veronese varieties i…

Chow-Lam 恢复

Chow-Lam Recovery

本文研究 Grassmannian 子簇能否由其 Chow-Lam 形式及线性投影恢复，给出恢复的必要条件，并构造与射影空间情形相反、无法恢复的反例族。

Chow Quotients of Grassmannians II

We consider Kapranov's Chow quotient compactification of the moduli space of ordered n-tuples of hyperplanes in P^{r-1} in linear general position. For r=2 this is canonically identified with the Grothendieck-Knudsen compactification of M_{0,n} which has among others the nice properties 1) Modular meaning: stable pointed rational curves 2) Canonical description of limits of one parameter degenerations 3) Natural Mori theoretic meaning: log canonical compactification. We prove (1-2) generalize naturally to all (r,n), but that (3), which we view as the deepest, fails except possibly in the cases…

The Chow rings of $G_2$ and $Spin_7$

We compute $CH^*BG_2$ and $CH^*BSpin_7$, using in particular the stratification method introduced by Vezzosi. We also give some information on the Chow rings of the finite groups $G_2(q)$. This new version includes an appendix, which will be published on its own as an addendum. It explains how one can use our results to produce a counter-example to the conjecture, due to Totaro, which predicted that the Chow ring of a finite group was generated by transfers of Chern classes.

Segre行列式

The Segre Determinant

本文研究Segre行列式，计算其在不同坐标系下的形式，并证明其代表Grassmannian中通用的torus轨道的Chow-Lam形式，同时探讨其在代数视觉和Grassmannian Chow商中的应用。

On the Chow ring of Fano varieties of type $S2$

We show that certain Fano eightfolds (obtained as hyperplane sections of an orthogonal Grassmannian, and studied by Ito-Miura-Okawa-Ueda and by Fatighenti-Mongardi) have a multiplicative Chow-Künneth decomposition. As a corollary, the Chow ring of these eightfolds behaves like that of K3 surfaces.

Equivariant Chow classes of matrix orbit closures

Let $G$ be the product $GL_r(C) \times (C^\times)^n$. We show that the $G$-equivariant Chow class of a $G$ orbit closure in the space of $r$-by-$n$ matrices is determined by a matroid. To do this, we split the natural surjective map from the $G$ equvariant Chow ring of the space of matrices to the torus equivariant Chow ring of the Grassmannian. The splitting takes the class of a Schubert variety to the corresponding factorial Schur polynomial, and also has the property that the class of a subvariety of the Grassmannian is mapped to the class of the closure of those matrices whose row span is …

On the Chow ring of Fano varieties of type $S6$

Fatighenti and Mongardi have defined Fano varieties of type S6 as zero loci of a certain vector bundle on the Grassmannian $\hbox{Gr}(2,10)$. These varieties have 3 Hodge structures of K3 type in their cohomology. We show that the Chow ring of these varieties also displays "K3 type" behaviour.

Resultants and Chow forms via Exterior Syzygies

Given a sheaf on a projective space P^n we define a sequence of canonical and easily computable Chow complexes on the Grassmannians of planes in P^n, generalizing the Beilinson monad on P^n. If the sheaf has dimension k, then the Chow form of the associated k-cycle is the determinant of the Chow complex on the Grassmannian of planes of codimension k+1. Using the theory of vector bundles and the canonical nature of the complexes we are able to give explicit determinantal and Pfaffian formulas for resultants in some cases where no polynomial formulas were known. For example, the Horrocks-Mumford…

On the Grassmannian homology of $\mathbbm{F}_2$ and $\mathbbm{F}_3$

We prove the vanishing of the subgroup of Bloch's cubical higher Chow groups $CH^2(\text{Spec}(\MF_p),3)$, $p=2,3$, generated by the images of corresponding projective Grassmannian homology groups ${}^PGH_1^2(\MF_p)$ using computer calculations.

Some new Fano varieties with a multiplicative Chow-Künneth decomposition

Let $Y$ be a smooth dimensionally transverse intersection of the Grassmannian $\hbox{Gr}(2,n)$ with 3 Plücker hyperplanes. We show that $Y$ admits a multiplicative Chow-Künneth decomposition, in the sense of Shen-Vial. As a consequence, a certain tautological subring of the Chow ring of powers of $Y$ injects into cohomology.

Smooth Schubert varieties and generalized Schubert polynomials in algebraic cobordism of Grassmannians

We provide several ingredients towards a generalization of the Littlewood-Richardson rule from Chow groups to algebraic cobordism. In particular, we prove a simple product-formula for multiplying classes of smooth Schubert varieties with any Bott-Samelson class in algebraic cobordism of the grassmannian. We also establish some results for generalized Schubert polynomials for hyperbolic formal group laws.

An Additive Basis for the Chow Ring of \bar{M}_{0,2}(P^r,2)

We begin a study of the intersection theory of the moduli spaces of degree two stable maps from two-pointed rational curves to arbitrary-dimensional projective space. First we compute the Betti numbers of these spaces using Serre polynomial and equivariant Serre polynomial methods developed by E. Getzler and R. Pandharipande. Then, via the excision sequence, we compute an additive basis for their Chow rings in terms of Chow rings of nonlinear Grassmannians, which have been described by Pandharipande. The ring structure of one of these Chow rings is addressed in a sequel to this paper.

Automorphism groups of Grassmann codes

We use a theorem of Chow (1949) on line-preserving bijections of Grassmannians to determine the automorphism group of Grassmann codes. Further, we analyze the automorphisms of the big cell of a Grassmannian and then use it to settle an open question of Beelen et al. (2010) concerning the permutation automorphism groups of affine Grassmann codes. Finally, we prove an analogue of Chow's theorem for the case of Schubert divisors in Grassmannians and then use it to determine the automorphism group of linear codes associated to such Schubert divisors. In the course of this work, we also give an alt…

加权爆破的整 Chow 环

The integral Chow ring of weighted blow-ups

该研究给出加权爆破的整 Chow 环计算公式，同时得到加权射影栈丛的整 Chow 环、加权爆破的 Gysin 同态公式与分裂原理的推广，并在附录中算出加权爆破的陈类。

Positive configuration space

We define and study the totally nonnegative part of the Chow quotient of the Grassmannian, or more simply the nonnegative configuration space. This space has a natural stratification by positive Chow cells, and we show that nonnegative configuration space is homeomorphic to a polytope as a stratified space. We establish bijections between positive Chow cells and the following sets: (a) regular subdivisions of the hypersimplex into positroid polytopes, (b) the set of cones in the positive tropical Grassmannian, and (c) the set of cones in the positive Dressian. Our work is motivated by connecti…

Drinfeld-Gaitsgory-Vinberg 插值 Grassmannian 与几何 Satake 等价（附录由 Dennis Gaitsgory 撰写）

Drinfeld-Gaitsgory-Vinberg interpolation Grassmannian and geometric Satake equivalence (with appendix by Dennis Gaitsgory)

本文证明Schieder猜想，将仿射Grassmannian中相反半无限轨道交集的顶部紧支撑上同调形成的双代数等同于Langlands对偶正幂零子代数的泛包络代数，并构造其在几何Satake纤维函子上的作用，同时提出任意对称Kac-Moody情形的Coulomb分支构造。

The Equivariant Chow rings of quot schemes

We give a presentation for the (integral) torus-equivariant Chow ring of the quot scheme, a smooth compactification of the space of rational curves of degree d in the Grassmannian. For this presentation, we refine Evain's extension of the method of Goresky, Kottwitz, and MacPherson to express the torus-equivariant Chow ring in terms of the torus-fixed points and explicit relations coming from the geometry of families of torus-invariant curves. As part of this calculation, we give a complete description of the torus-invariant curves on the quot scheme and show that each family is a product of p…

计算二次空间曲线的 Chow 簇

Computing the Chow variety of quadratic space curves

本文研究三维空间直线 Grassmannian 中二次曲面的余迷向超曲面子簇，按 GKZ 理论将其分解为三类轨迹，并计算相应理想。

$\boldsymbol{\bar{\rm M}_{1,n}}$的穿墙整Chow环

Wall-crossing integral Chow rings of $\overline{\mathcal M}_{1,n}$

本文通过归纳计算Smyth提出的替代紧化的整Chow环，得到了$n=3,4$时$\bar{\text{M}}_{1,n}$的整Chow环，并指出$n\leq6$时该栈可由简单栈经加权胀缩得到。

Minimal bandwidth $\mathbb{C}^*$-actions on generalized Grassmannians

The bandwidth of a $\mathbb{C}^*$-action of a polarized pair $(X,L)$ is a natural measure of its complexity. In this paper we study $\mathbb{C}^*$-actions on rational homogeneous spaces, determining which provide minimal bandwidth. We prove that the minimal bandwidth is linked to the smallest coefficient of the fundamental weight, in a base of simple roots, which describes the variety as a marked Dynkin diagram. As a direct application of the results we study the Chow ring of the Cayley plane $\mathrm{E}_6(6)$.

Polylogarithms, regulators and Arakelov motivic complexes

We construct an explicit regulator map from the weigh n Bloch Higher Chow group complexto the weight n Deligne complex of a regular complex projective algebraic variety X. We define the Arakelovweight n motivic complex as the cone of this map shifted by one. Its last cohomology group is (a version of) the Arakelov Chow group defined by H. Gillet. and C.Soule. We relate the Grassmannian n-logarithms (defined as in [G5]) to geometry of the symmetric space for GL_n(C). For n=2 we recover Lobachevsky's formula for the volume of an ideal geodesic tetrahedron via the dilogarithm. Using the relations…

Cell decompositions and algebraicity of cohomology for quiver Grassmannians

We show that the cohomology ring of a quiver Grassmannian asssociated with a rigid quiver representation has property (S): there is no odd cohomology and the cycle map is an isomorphism; moreover, its Chow ring admits explicit generators defined over any field. From this we deduce the polynomial point count property. By restricting the quiver to finite or affine type, we are able to show a much stronger assertion: namely, that a quiver Grassmannian associated to an indecomposable (not necessarily rigid) representation admits a cellular decomposition. As a corollary, we establish a cellular dec…

曲线的对数Hilbert方案作为加权吹胀及其整环Chow环

Logarithmic Hilbert schemes of curves as weighted blow-ups and their integral Chow rings

本文研究了曲线的对数Hilbert方案作为加权吹胀的结构，并计算了其整环Chow环，利用了加权吹胀的Chow环公式和Castelnuovo准则的加权版本，恢复了对数Hilbert方案为堆栈的结果。

度为2的拟极化K3曲面模空间的周环

The Chow ring of the moduli space of degree $2$ quasi-polarized K3 surfaces

本文研究了度为2的拟极化K3曲面模空间的有理周环，确定了其生成元与关系，证明其由重言类组成并同构于偶上同调，同时显式计算了配对核。

Deligne's integrality theorem in unequal characteristic and rational points over finite fields; and Appendix (w/Pierre Deligne)

If $V$ is a smooth projective variety defined over a local field $K$ with finite residue field, so that its étale cohomology over the algebraic closure $\bar{K}$ is supported in codimension 1, then the mod $p$ reduction of a projective regular model carries a rational point. As a consequence, if the Chow group of 0-cycles of $V$ over a large algebraically closed field is trivial, then the mod $p$ reduction of a projective regular model carries a rational point.

$\mathbb{G}(1, 5)$ 中 $\mathrm{PGL}_3$ 轨道闭包的周环类

The Chow Ring Classes of $\mathrm{PGL}_3$ Orbit Closures in $\mathbb{G}(1, 5)$

本文研究平面圆锥曲线束构成的格拉斯曼簇在 PGL(V) 作用下的八个轨道，通过几何描述、枚举技巧和陈类计算，确定了各轨道闭包在周环中的类及其普吕克嵌入次数。

Arithmetic Intersection Theory on Flag Varieties

Let F be the complete flag variety over Spec(Z) with the tautological filtration 0 \subset E_1 \subset E_2 \subset ... \subset E_n=E of the trivial bundle E over F. The trivial hermitian metric on E(\C) induces metrics on the quotient line bundles L_i(\C). Let \hat{c}_1(L_i) be the first Chern class of L_i in the arithmetic Chow ring \hat{CH}(F) and x_i = -\hat{c}_1(L_i). Let h(X_1,...,X_n) be a polynomial with integral coefficients in the ideal <e_1,...,e_n> generated by the elementary symmetric polynomials e_i. We give an effective algorithm for computing the arithmetic intersection h(x_1,..…

Chow rings of stacks of prestable curves I

We study the Chow ring of the moduli stack $\mathfrak{M}_{g,n}$ of prestable curves and define the notion of tautological classes on this stack. We extend formulas for intersection products and functoriality of tautological classes under natural morphisms from the case of the tautological ring of the moduli space $\bar{\mathcal{M}}_{g,n}$ of stable curves. This paper provides foundations for the second part of the paper. In the appendix (joint with J. Skowera), we develop the theory of a proper, but not necessary projective, pushforward of algebraic cycles. The proper pushforward is necessary …

A motivic global Torelli theorem for isogenous K3 surfaces

We prove that the Chow motives of twisted derived equivalent K3 surfaces are isomorphic, not only as Chow motives (due to Huybrechts), but also as Frobenius algebra objects. Combined with a recent result of Huybrechts, we conclude that two complex projective K3 surfaces are isogenous (i.e. their second rational cohomology groups are Hodge isometric) if and only if their Chow motives are isomorphic as Frobenius algebra objects; this can be regarded as a motivic Torelli-type theorem. We ask whether, more generally, twisted derived equivalent hyper-Kaehler varieties have isomorphic Chow motives a…

The Chow motive of semismall resolutions

We consider proper, algebraic semismall maps f from a complex algebraic manifold X. We show that the topological Decomposition Theorem implies a "motivic" decomposition theorem for the rational algebraic cycles of X and, in the case X is compact, for the Chow motive of X.The result is a Chow-theoretic analogue of Borho-MacPherson's observation concerning the cohomology of the fibers and their relation to the relevant strata for f. Under suitable assumptions on the stratification, we prove an explicit version of the motivic decomposition theorem. The assumptions are fulfilled in many cases of i…

Maximal orthogonal grassmannians of quadratic forms of dimensions up to $22$

Let $X$ be a connected component of the maximal orthogonal grassmannian of a generic $n$-dimensional quadratic form $q$ with trivial Clifford invariant. Consider the canonical epimorphism $ϕ$ from the Chow ring of $X$ to the associated graded ring of the coniveau filtration on the Grothendieck ring of $X$. In \cite{Kar2018} Karpenko proved that $ϕ$ is an isomorphism for all $n\leq 12$ (conjecturally for all $n$). Recently, in \cite{Yagita} Yagita showed that $ϕ$ is not an isomorphism for $n=17, 18$. In the present paper, together with Yagita's results for $n=17,18$, we show that the map $ϕ$ is…

Cherednik algebras and Hilbert schemes in characteristic p (with an appendix by Pavel Etingof)

We prove a localization theorem for the type A rational Cherednik algebra H_c=H_{1,c} over an algebraic closure of the finite field F_p. In the most interesting special case where the parameter c takes values in F_p, we construct an Azumaya algebra A_c on Hilb^n, the Hilbert scheme of n points in the plane, such that the algebra of global sections of A_c is isomorphic to H_c. Our localisation theorem provides an equivalence between the bounded derived categories of H_c-modules and sheaves of coherent A_c-modules on the Hilbert scheme, respectively. Furthermore, we show that the Azumaya algebra…

On quantum cohomology of Grassmannians of isotropic lines, unfoldings of $A_n$-singularities, and Lefschetz exceptional collections

The subject of this paper is the big quantum cohomology rings of symplectic isotropic Grassmannians $\text{IG}(2, 2n)$. We show that these rings are regular. In particular, by "generic smoothness", we obtain a conceptual proof of generic semisimplicity of the big quantum cohomology for $\text{IG}(2, 2n)$. Further, by a general result of Claus Hertling, the regularity of these rings implies that they have a description in terms of isolated hypersurface singularities, which we show in this case to be of type $A_{n-1}$. By the homological mirror symmetry conjecture, these results suggest the exis…

源自 Coulomb 分支的等变导出 Satake 范畴中的环对象（附 Gus Lonergan 撰写的附录）

Ring objects in the equivariant derived Satake category arising from Coulomb branches (with an appendix by Gus Lonergan)

本文证明三元组簇到仿射 Grassmannian 态射的对偶化复形正像构成等变导出 Satake 范畴中的环对象，并将既有构造推广到任意交换环对象，同时研究星形箭图对应的 Coulomb 分支。

有理齐次簇中的极大不相交 Schubert 环

Maximal disjoint Schubert cycles in rational homogeneous varieties

本文通过研究经典类型有理齐次簇的 Chow 环中低余维数有效零因子及有效良好可除性，探讨了这些簇之间非常数映射的存在性，推广了射影空间和 Grassmann 簇的已知结果。

超椭圆 Prym 对模栈的积分 Chow 环 III

The Integral Chow Rings of the Moduli Stacks of Hyperelliptic Prym Pairs III

本文通过商栈描述和刚性化映射的根 gerbe 判别，完成了超椭圆 Prym 对模栈所有不可约分支积分 Chow 环的计算，仅剩一个奇亏格特殊情形未决。

Schémas de Fano

Let X be a subvariety of $P^n$ defined by equations of degrees $ d =(d_1,...,d_s)$, over an algebraically closed field k of any characteristic. We study properties of the Fano scheme $F_r(X)$ that parametrizes linear subspaces of dimension r contained in X. We prove that $F_r(X)$ is connected and smooth of the expected dimension for n big enough (this was previously known in characteristic 0 or for r=1). Using Bott's theorem, we prove a vanishing theorem for certain bundles on the Grassmannian and use it to calculate the cohomology groups of $F_r(X)$ in degree $\le \dim X-2r$, and to prove tha…

从 Yang-Baxter 代数看 Grassmannians 的量子 K--理论

Quantum K--theory of Grassmannians from a Yang-Baxter algebra

本文构造了描述 $5$-顶点 Yang-Baxter 代数在 Grassmannians 量子 K-环上作用的几何算子，证明了生成子作用的几何解释，并给出了不动点类的量子化及若干应用。