Ilya Boldyrev, Sergey Gaifullin
In this paper we prove criteria for a nonnormal toric variety to be flexible, to be rigid and to be almost rigid. For rigid and almost rigid toric varieties we describe the automorphism group explicitly.
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We prove the equality of the Makar-Limanov invariant and the modified Makar-Limanov invariant in the case of not necessary normal affine toric varieties. Also we give a combinatorial description of these invariants.
We prove that the automorphism group of a toric Deligne-Mumford stack is isomorphic to the $2$-group associated to the stacky fan.
The automorphism group of a projective bundle P(E) over a simplicial toric variety is described when the bundle E is a direct sum of line bundles. Applications to study of moduli of complete intersections on toric varieties, including Calabi Yau m-folds and Del Pezzo surfaces, are indicated.
On the connectedness of the automorphism group of an affine toric variety
本研究从组合与除子类群角度给出仿射环面簇自同构群连通性的判别准则，刻画非退化仿射环面簇自同构群的分支群，并证明其连通分支数有限。
Automorphism groups of non-normal affine toric surfaces
研究非正规仿射环面曲面的自同构群，发现当奇异轨迹含一维环面轨道时性质成立，否则可能不成立，并构造反例。
We give an explicit description of the automorphism group of a product of complete toric varieties over an arbitrary field in terms of the respective automorphism groups of its components. More precisely, we prove that, up to permutation of isomorphic components, an automorphism of a product corresponds to a product of automorphisms of its components. We also reprove, in modern language, the classic result by Demazure describing the group-scheme of automorphisms of a complete toric variety over an arbitrary field.
Let X be a complete toric variety and Aut(X) be the automorphism group. We give an explit description of Aut(X)-orbits on X. In particular, we show that Aut(X) acts on X transitively if and only if X is a product of projective spaces.
We calculate the automorphism group of a complete toric variety $X$ with torus $T_M$. We prove that the radical unipotent of $Aut_k^0X$ is a semidirect product of additive groups, the reductive part is a quotient of a product of lineal groups and we give the action of linear groups on the additive groups. We also prove that $Aut_kX/Aut_k^0X$ is a quotient of the group of automorphisms of $M$ leaving invariant the fan.
Let X be an affine toric variety. The total coordinates on X provide a canonical presentation of X as a quotient of a vector space by a linear action of a quasitorus. We prove that the orbits of the connected component of the automorphism group Aut(X) on X coincide with the Luna strata defined by the canonical quotient presentation.
Complete toric varieties with semisimple automorphism group
该研究通过分析趋形体的1骨架和风扇结构，提出判断其是否可分解为射影空间乘积的准则，并证明半单自同构群的条件下的结论。
On the automorphism group of non-necessarily normal affine toric varieties
本文刻画了无环面因子的正规仿射环面曲面何时存在同自同构群的非正规仿射环面曲面，并通过对齐次局部幂零导子的分类实现了对非正规环面簇上加法群作用的完整分类。
On the characterization of affine toric varieties by their automorphism group
本文证明了正规仿射环面簇在特定范畴中由自同构群唯一决定的充要条件，并指出代数环面情形下的维数限制结果是最优的。
Automorphisms of toric varieties and Gale duality
本文利用Gale对偶分类了满足自同构群具有开轨道且补集无除子的完备环面三维簇，并确定了自同构群在光滑点集上可递的簇。
Toric subvarieties of projective space are classified up to projective automorphisms.
We give equivalent and sufficient criteria for the automorphism group of a complete toric variety, respectively a Gorenstein toric Fano variety, to be reductive. In particular we show that the automorphism group of a Gorenstein toric Fano variety is reductive, if the barycenter of the associated reflexive polytope is zero. Furthermore a sharp bound on the dimension of the reductive automorphism group of a complete toric variety is proven by studying the set of Demazure roots.
Borel subgroups of the automorphism groups of affine toric surfaces
本文研究了仿射平面的循环商自同构群的 Borel 子群与极大可解子群，证明其分为两类并分别具有一个或两个共轭类，利用 Bass-Serre-Tits 理论完成证明。
In 2013 Bazhov proved a criterium for two points on a complete toric variety to lie in the same orbit of the neutral component of automorphism group. This criterium is in terms of divisor class group. Arzhantsev-Bazhov (2013) obtained a similar criterium for affine toric varieties. We prove a necessary condition similar this criteria to the cases of affine and projective horospherical varieties.
We study aspects related to Kontsevich's homological mirror symmetry conjecture in the case of Calabi-Yau complete intersections in toric varieties. In a 1996 lecture at Rutgers University, Kontsevich indicated how his proposal implies that the groups of automorphisms of the two types of categories involved in the homological mirror symmetry conjecture should also be identified. Our main results provide an explicit geometric construction of the correspondence between the automorphisms of the two types of categories.
In this paper we prove that if two normal affine surfaces $S$ and $S'$ have isomorphic automorphism groups, then every connected algebraic group acting regularly and faithfully on $S$ acts also regularly and faithfully on $S'$. Moreover, if $S$ is non-toric, we show that the dynamical type of a 1-torus action is preserved in presence of an additive group action. We also show that complex affine toric surfaces are determined by the abstract group structure of their regular automorphism groups in the category of complex normal affine surfaces using properties of the Cremona group. As a generaliz…
Equivariant unirationality of toric varieties
本文研究环面簇在有限群作用下的等变单有理性，提出挠子理论障碍并证明其对环面自同构诱导作用的充分性。
Borel subalgebras of Lie algebras of vector fields
本文研究了仿射代数曲面自同构群的李代数中可积Borel子代数的结构与分类，揭示其与Borel子群切代数的关系。
Automorphism groups of toroidal horospherical varieties
本文研究了toroidal horospherical varieties的自同构群结构，通过分析Demazure根的特征，给出了判断此类品种自同构群可约性的标准，并应用该结果证明了某些P^1束的K-不稳定性质。
We say that a group G acts infinitely transitively on a set X if for every integer m the induced diagonal action of G is transitive on the cartesian mth power of X with the diagonals removed. We describe three classes of affine algebraic varieties such that their automorphism groups act infinitely transitively on their smooth loci. The first class consists of affine cones over flag varieties, the second of non-degenerate affine toric varieties, and the third of iterated suspensions over affine varieties with infinitely transitive automorphism groups of a reinforced type.
We prove that up to automorphisms a line admits a unique embedding into the regular part of of a simplicial toric variety of dimension n>=4 over an algebraically closed field of characteristic zero which is smooth in codimension 2.
In this paper we describe orbits of automorphism group on a horospherical variety in terms of degrees of homogeneous with respect to natural grading locally nilpotent derivations. In case of (may be non-normal) toric varieties a description of orbits of automorphism group in terms of corresponding weight monoid is obtained.
In this note we study linear systems on complete toric varieties $X$ with an invariant point, whose orbit under the action of the automorphism group of $X$ contains the dense torus $T$ of $X$. We give a characterization of such varieties in terms of its defining fan and introduce a new definition of expected dimension of linear systems which consider the contribution given by certain toric subvarieties. Finally, we study degenerations of linear systems on these toric varieties induced by toric degenerations.
We describe the weight filtration in the cohomology of toric varieties. We present a role of the Frobenius automorphism in an elementary way. We prove that equivariant intersection homology of an arbitrary toric variety is pure. We obtain results concerning Koszul duality: nonequivariant intersection cohomology is equal to the cohomology of the Koszul complex $IH_T^*(X)\otimes H^*(T)$. We also describe the weight filtration in $IH^*(X)$.
For an arbitrary field K, let I be an ideal in the ring K[[x,y]] expressible as a polynomial in either the pair of ideals (x, y^4) and (x,y) or the pair (x,y^3) and (x^2, y). Let G be the group of automorphisms of K[[x,y]] sending the ideal (x,y^2) to itself. Then the normalization of the closure of the G orbit of I is a toric variety. We use the interplay of the properties of Hilbert schemes and toric varieties to study these spaces.
A non-degenerate toric variety $X$ is called $S$-homogeneous if the subgroup of the automorphism group $\text{Aut}(X)$ generated by root subgroups acts on $X$ transitively. We prove that maximal $S$-homogeneous toric varieties are in bijection with pairs $(P,\mathcal{A})$, where $P$ is an abelian group and $\mathcal{A}$ is a finite collection of elements in $P$ such that $\mathcal{A}$ generates the group $P$ and for every $a\in\mathcal{A}$ the element $a$ is contained in the semigroup generated by $\mathcal{A}\setminus\{a\}$. We show that any non-degenerate homogeneous toric variety is a big o…
Isolated torus invariants and automorphism groups of rigid varieties
该研究针对刚性仿射簇自同构群单位分支为环面的猜想，在环面簇与复杂度1环面作用簇上完成证明，给出刚性簇上m-悬垂的刚性判别准则并研究对应自同构群。
We prove that for each positive integer $n$ there exists a positive number $ε_n$ so that $n$-dimensional toric quotient singularities satisfy the ACC for mld's on the interval $(0,ε_n)$. In the course of the proof, we will show a geometric Jordan property for finite automorphism groups of affine toric varieties.
Radiant toric varieties and unipotent group actions
该研究针对具有开轨道的极大幂零子群作用的完备环面簇，刻画其性质，分析对应扇的Demazure根、幂零子群结构及相关正则子群，推进环面簇与群作用领域的研究。
Normal affine algebraic varieties in characteristic 0 are uniquely determined (up to isomorphism) by the Lie algebra of derivations of their coordinate ring. This is not true without the hypothesis of normality. But, we show that (in general, non-normal) toric varieties defined by simplicial affine semigroups are uniquely determined by their Lie algebra if they are supposed to be Cohen-Macaulay of dimension at least 2 or Gorenstein of dimension 1. Moreover, every automorphism of the Lie algebra is induced from a unique automorphism of the variety and every derivation of the Lie algebra is inne…
Let G be a connected reductive complex algebraic group acting on a smooth complete complex algebraic variety X. We assume that X under the action of G is a regular embedding, a condition satisfied in particular by smooth toric varieties and flag varieties. For any set D of G-stable prime divisors, we study the action on X of the connected automorphism group of X stabilizing D. We determine a Levi subgroup A of this automorphism group, and we compute relevant invariants of X as a spherical A-variety. As a byproduct, we obtain a description of the open A-orbit on X and the inclusion relation bet…
We study $A$-hypergeometric functions introduced by Gelfand-Kapranov-Zelevinsky and prove a formula for the eigenvalues of their monodromy automorphisms defined by the analytic continuaions along large loops contained in complex lines parallel to the coordinate axes. A method of toric compactifications will be used to prove our main theorem.
Demushkin's Theorem says that any two toric structures on an affine variety X are conjugate in the automorphism group of X. We provide the following extension: Let an (n-1)-dimensional torus T act effectively on an n-dimensional affine toric variety X. Then T is conjugate in the automorphism group of X to a subtorus of the big torus of X.
We study toric varieties over a field k that split in a Galois extension K/k using Galois cohomology with coefficients in the toric automorphism group. Part of this Galois cohomology fits into an exact sequence induced by the presentation of the class group of the toric variety. This perspective helps to compute the Galois cohomology, particularly for cyclic Galois groups. We use Galois cohomology to classify k-forms of projective spaces when K/k is cyclic, and we also study k-forms of surfaces.
An ind-variety is an inductive limit of closed embeddings of algebraic varieties and an ind-group is a group object in the category of ind-varieties. These notions were first introduced by Shafarevich in the study of the automorphism group of affine spaces and have been studied by many authors afterwards. An ind-torus is an ind-group obtained as an inductive limit of closed embeddings of algebraic tori that are also algebraic group homomorphisms. In this paper, we introduce the natural definition of toric ind-varieties as ind-varieties having an ind-torus as an open set and such that the actio…
Let $K/k$ be a finite Galois extension, $G=\text{Gal}(K/k)$, $Σ$ be a fan in a lattice $N$ and $X_Σ$ be an associated toric variety over $k$. It is well known that the set of $K/k$-forms of $X_Σ$ is in bijection with $H^1(G,\text{Aut}_Σ^T)$, where $\text{Aut}_Σ^T$ is an algebraic group of toric automorphisms of $X_Σ$. In this paper, we suggest an algorithm to compute $H^1(G,\text{Aut}_Σ^T)$ and find that followings can be classified via this algorithm : $K/k$-forms of all toric surfaces, $K/k$-forms of all 3-dimensional affine toric varieties with no torus factor, $K/k$-forms of all 3-dimensio…
Maximal commutative unipotent subgroups and a characterization of affine spherical varieties
本文描述了不可约仿射簇自同构群的极大交换幂幺子群，证明群同构保持幂幺元素，并利用此结果证明自同构群能检测球面性与权幺半群，进而刻画了仿射环面簇与光滑仿射球面簇由其自同构群唯一确定的性质。
In this paper we generalize the algebraic density property to not necessarily smooth affine varieties relative to some closed subvariety containing the singular locus. This property implies the remarkable approximation results for holomorphic automorphisms of the Andersén-Lempert theory. We show that an affine toric variety X satisfies this algebraic density property relative to a closed T-invariant subvariety Y if and only if X-Y is different from T. For toric surfaces we are able to classify those which posses a strong version of the algebraic density property (relative to the singular locus…
This submission consists of two papers: 1) an erratum that corrects an error in the proof of Proposition 4.3 in my paper "The Homogeneous Coordinate Ring of a Toric Variety", and 2) the original (unchanged) version of the paper, published in 1995. The original paper introduced the homogeneous coordinate ring of a toric variety (now called the total coordinate ring or Cox ring) and gave a quotient construction. The paper also studied sheaves on a toric variety, and in Section 4 described its automorphism group. The error in the proof of Proposition 4.3 resulted from the faulty assumption that a…
Permutation Representations on Cohomology of Toric Varieties
本文证明Stanley关于环面簇上同调表示是否为置换表示的开放问题，对所有光滑射影环面簇均成立，无需适当性假设，证明受环面镜像对称启发。
We study the Cox realization of an affine variety, i.e., a canonical representation of a normal affine variety with finitely generated divisor class group as a quotient of a factorially graded affine variety by an action of the Neron-Severi quasitorus. The realization is described explicitly for the quotient space of a linear action of a finite group. A universal property of this realization is proved, and some results on the divisor theory of an abstract semigroup emerging in this context are given. We show that each automorphism of an affine variety can be lifted to an automorphism of the Co…
Culler and Vogtmann defined a simplicial space $O(g)$ called outer space to study the outer automorphism group of the free group $F_g$. Using representation theoretic methods, we give an embedding of $O(g)$ into the analytification of $\mathcal{X}(F_g, SL_2(\mathbb{C})),$ the $SL_2(\mathbb{C})$ character variety of $F_g,$ reproving a result of Morgan and Shalen. Then we show that every point $v$ contained in a maximal cell of $O(g)$ defines a flat degeneration of $\mathcal{X}(F_g, SL_2(\mathbb{C}))$ to a toric variety $X(P_Γ)$. We relate $\mathcal{X}(F_g, SL_2(\mathbb{C}))$ and $X(v)$ topologi…
On a combinatorial description of the Gorenstein index for varieties with torus action
本文证明复杂度一的环面作用 Fano 簇及一般排列簇的 Gorenstein 指数可由反典范复形的格距离读出，并据此界定近齐次 Fano 三维簇的定义数据。
The geometric Merkurjev-Panin Conjecture for the Cox category
本文证明了Cox范畴中几何Merkurjev-Panin猜想的强版本成立，揭示了该范畴在研究代数簇同调代数中的重要性。
$q$-Painlevé equations on cluster Poisson varieties via toric geometry
本文通过环面几何建立$q$-Painlevé方程与簇泊松簇的联系，引入$q$-Painlevé型种子并分类其突变等价类，与Sakai分类一致，并将$q$-Painlevé系统实现为簇泊松簇上的自同构。
A two-step approach to Chow quotients
本文提出通过投影托里克品种和其有理数自同构群来编码楚 quotient 的几何结构，并应用于某些特定的有理数 homogeneous 变形。
Can an ideal I in a polynomial ring k[x] over a field be moved by a change of coordinates into a position where it is generated by binomials $x^a - cx^b$ with c in k, or by unital binomials (i.e., with c = 0 or 1)? Can a variety be moved into a position where it is toric? By fibering the G-translates of I over an algebraic group G acting on affine space, these problems are special cases of questions about a family F of ideals over an arbitrary base B. The main results in this general setting are algorithms to find the locus of points in B over which the fiber of F - is contained in the fiber o…
Automorphisms and deformations of regular semisimple Hessenberg varieties
研究正则半单Hessenberg流形的自同构与变形，证明其模空间结构及上同调性质。
Weight sensitivity in K-stability of Fano varieties
本文证明了特定球面Fano三维簇中加权K-多稳定性等价于加权Futaki不变量消失，并在Mori-Mukai族2-29及高维二次曲面中展示了该性质不成立的显式反例。
We introduce a notion of stable spherical variety which includes the spherical varieties under a reductive group $G$ and their flat equivariant degenerations. Given any projective space $\bP$ where $G$ acts linearly, we construct a moduli space for stable spherical varieties over $\bP$, that is, pairs $(X,f)$, where $X$ is a stable spherical variety and $f : X \to \bP$ is a finite equivariant morphism. This space is projective, and its irreducible components are rational. It generalizes the moduli space of pairs $(X,D)$, where $X$ is a stable toric variety and $D$ is an effective ample Cartier…
Real Legendrian subvarieties are classical objects of differential geometry and classical mechanics and they have been studied since antiquity. However, complex Legendrian subvarieties are much more rigid and have more exceptional properties. The most remarkable case is the Legendrian subvarieties of projective space and prior to the author's research only few smooth examples of these were known. The first series of results of this thesis is related to the automorphism group of any Legendrian subvariety in any projective contact manifold. The connected component of this group (under suitable m…
In this paper we study group-based Markov models of evolution and their mixtures. In the algebreo-geometric setting, group-based phylogenetic tree models correspond to toric varieties, while their mixtures correspond to secant and join varieties. Determining properties of these secant and join varieties can aid both in model selection and establishing parameter identifiability. Here we explore the first natural geometric property of these varieties: their dimension. The expected projective dimension of the join variety of a set of varieties is one more than the sum of their dimensions. A join …
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