Klaus Altmann, Jan Arthur Christophersen
We study the deformation theory of projective Stanley-Reisner schemes associated to combinatorial manifolds. We achieve detailed descriptions of first order deformations and obstruction spaces. Versal base spaces are given for certain Stanley-Reisner surfaces.
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We construct degenerations of Mukai varieties and linear sections thereof to special unobstructed Fano Stanley-Reisner schemes corresponding to convex deltahedra. This can be used to find toric degenerations of rank one index one Fano threefolds. In the second part we find many higher dimensional unobstructed Fano and Calabi-Yau Stanley-Reisner schemes. The main result is that the Stanley-Reisner ring of the boundary complex of the dual polytope of the associahedron has trivial $T^2$.
Let $Q^*$ denote the dual of the quotient bundle on the Grassmannian $G(2,n)$. We prove that the ideal of $Q^*$ in its natural embedding has initial ideal equal to the Stanley-Reisner ideal of a certain unobstructed simplicial complex. Furthermore, we show that the coordinate ring of $Q^*$ has no infinitesimal deformations for $n>5$.
The versal deformation of Stanley-Reisner schemes associated to equivelar triangulations of the torus is studied. The deformation space is defined by binomials and there is a toric smoothing component which I describe in terms of cones and lattices. Connections to moduli of abelian surfaces are considered. The case of the Möbius torus is especially nice and leads to a projective Calabi-Yau 3-fold with Euler number 6.
We combine work of Cox on the total coordinate ring of a toric variety and results of Eisenbud-Mustata-Stillman and Mustata on cohomology of toric and monomial ideals to obtain a formula for computing the Euler characteristic of a Weil divisor D on a complete simplicial toric variety in terms of graded pieces of the Cox ring and Stanley-Reisner ring. The main point is to use Alexander duality to pass from the toric irrelevant ideal, which appears in the computation of the Euler characteristic of D, to the Stanley-Reisner ideal of the fan, which is used in defining the Chow ring. The formula al…
Simplicial complexes X provide commutative rings A(X) via the Stanley-Reisner construction. We calculated the cotangent cohomology, i.e., T1 and T2 of A(X) in terms of X. These modules provide information about the deformation theory of the algebro geometric objects assigned to X.
We consider the convex geometry of the cone of nonnegative quadratics over Stanley-Reisner varieties. Stanley-Reisner varieties (which are unions of coordinate planes) are amongst the simplest real projective varieties, so this is potentially a starting point that can generalize to more complicated real projective varieties. This subject has some suprising connections to algebraic topology and category theory, which we exploit heavily in our work. These questions are also valuable in applied math, because they directly translate to questions about positive semidefinite (PSD) matrices. In parti…
We prove that the Frobenius algebra of the injective hull of a complete Stanley-Reisner ring as well as its Matlis dual notion of Cartier algebra can be only principally generated or infinitely generated. As a consequence we are able to show that the set of F-jumping numbers of generalized test ideals associated to complete Stanley-Reisner rings form a discrete set.
We give a purely algebraic proof of the hypersurface case of Toric Residue Mirror Conjecture recently proposed by Batyrev and Materov.
Calabi-Yau manifolds are important objects in algebraic geometry and in theoretical physics. A hypothesis of mirror symmetry is that Calabi-Yau manifolds of dimension 3 come in pairs, with the Hodge numbers of one manifold mirroring the Hodge numbers of the other. In this thesis, Calabi-Yau manifolds are constructed by smoothing Stanley-Reisner schemes of triangulations of 3-spheres. The triangulations of the 3-sphere with 7 or 8 vertices have been constructed and classified by Grünbaum and Sreedharan (1967). In this thesis we characterize the Calabi-Yau manifolds obtained from the triangulati…
A geometrization of Stanley--Reisner theory
本文提出Stanley--Reisner对应的几何解释，将其推广至概形，并用一个元素的域进行诠释。
In the present note we study Waldschmidt constants of Stanley-Reisner ideals of a hypergraph and a graph with vertices forming a bipyramid over a planar n-gon. The case of the hypergraph has been studied by Bocci and Franci. We reprove their main result. The case of the graph is new. Interestingly, both cases provide series of ideals with Waldschmidt constants descending to 1. It would be interesting to known if there are bounded ascending sequences of Waldschmidt constants.
Let $Δ$ be a simplicial complex. We study the expansions of $Δ$ mainly to see how the algebraic and combinatorial properties of $Δ$ and its expansions are related to each other. It is shown that $Δ$ is Cohen-Macaulay, sequentially Cohen-Macaulay, Buchsbaum or $k$-decomposable, if and only if an arbitrary expansion of $Δ$ has the same property. Moreover, some homological invariants like the regularity and the projective dimension of the Stanley-Reisner ideals of $Δ$ and those of their expansions are compared.
Complete simplicial fans, Stanley--Reisner rings, and equivariant h-polynomials
本文推导了有限群作用于完备单纯形扇的Stanley-Reisner环的Artinian约简的分层特征公式，基于等变h多项式，并研究了该群在关联的典范流形上同调的表示。
In this article we associate to every lattice ideal $I_{L,ρ}\subset K[x_1,..., x_m]$ a cone $σ$ and a graph $G_σ$ with vertices the minimal generators of the Stanley-Reisner ideal of $σ$. To every polynomial $F$ we assign a subgraph $G_σ(F)$ of the graph $G_σ$. Every expression of the radical of $I_{L,ρ}$, as a radical of an ideal generated by some polynomials $F_1,..., F_s$ gives a spanning subgraph of $G_σ$, the $\cup_{i=1}^s G_σ(F_i)$. This result provides a lower bound for the minimal number of generators of $I_{L,ρ}$ and therefore improves the generalized Krull's principal ideal theorem f…
This paper introduces two new notions of graded linear resolution and graded linear quotients, which generalize the concepts of linear resolution property and linear quotient for modules over the polynomial ring $A=k[x_1, \dots ,x_n]$. Besides, we compare graded linearity with componentwise linearity in general. For modules minimally generated by a regular sequence in a maximal ideal of $A$, we show that graded linear quotients imply graded linear resolution property for the colon ideals. On the other hand, we provide specific characterizations of graded linear resolution property for the Stan…
Characterization of Stanley-Reisner varieties by their automorphism group
本文利用组合工具研究Stanley-Reisner簇的自同构ind群，证明完全外露复形可由其ind群唯一确定，稳定后任意复形的乘积簇也满足该性质，还给出完全隐藏复形的自同构群形式及应用准则。
K-rings of smooth toric varieties via piecewise-exponential functions
本文通过分段指数函数描述光滑赋值簇的K环，提出将分段指数函数环作为扇的Stanley-Reisner环的商环，从而得到与整数Chow环作为Stanley-Reisner环商环类似的K环呈现方法。
We present criteria for the Cohen-Macaulayness of a monomial ideal in terms of its primary decomposition. These criteria allow us to use tools of graph theory and of linear programming to study the Cohen-Macaulayness of monomial ideals which are intersections of prime ideal powers. We can characterize the Cohen-Macaulayness of the second symbolic power or of all symbolic powers of a Stanley-Reisner ideal in terms of the simplicial complex. These characterizations show that the simplicial complex must be very compact if some symbolic power is Cohen-Macaulay. In particular, all symbolic powers a…
Higher cotangent cohomology for Stanley-Reisner rings
受Altmann和Christophersen工作的启发，研究了与单纯复形K相关的Stanley-Reisner环S_K的余切上同调T^i_{S_K}（i≥3）的分次部分，给出了T^3和T^4的完全拓扑描述，并应用于球面等情形。
We study the intersections of general Schubert varieties X_w with permuted big cells, and give an inductive degeneration of each such "Schubert patch" to a Stanley-Reisner scheme. Similar results had been known for Schubert patches in various types of Grassmannians. We maintain reducedness using the results of [Knutson 2007] on automatically reduced degenerations, or through more standard cohomology-vanishing arguments. The underlying simplicial complex of the Stanley-Reisner scheme is a subword complex, as introduced for slightly different purposes in [Knutson-Miller 2004], and is homeomorphi…
We show in this paper that the principal component of the first order jet scheme over the classical determinantal variety of m x n matrices of rank at most 1 is arithmetically Cohen-Macaulay, by showing that an associated Stanley-Reisner simplicial complex is shellable.
We provide a new foundation for combinatorial commutative algebra and Stanley-Reisner theory using the partition complex introduced in [Adi18]. One of the main advantages is that it is entirely self-contained, using only a minimal knowledge of algebra and topology. On the other hand, we also develop new techniques and results using this approach. In particular, we provide - A novel, self-contained method of establishing Reisner's theorem and Schenzel's formula for Buchsbaum complexes. - A simple new way to establish Poincaré duality for face rings of manifolds, in much greater generality and p…
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