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Connor Sawaske
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There are a large number of theorems detailing the homological properties of the Stanley--Reisner ring of a simplicial complex. Here we attempt to generalize some of these results to the case of a simplicial poset. By investigating the combinatorics of certain modules associated with the face ring of a simplicial poset from a topological viewpoint, we extend some results of Miyazaki and Grabe to a wider setting.
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Let $A$ be a regular domain containing a field $K$ of characteristic zero, $G$ be a finite subgroup of the group of automorphisms of $A$ and $B=A^G$ be the ring of invariants of $G$. Let $S= A[X_1,ldots, X_m]$ and $R= B[X_1, ldots, X_m]$ be standard graded with $ deg A=0$, $ deg B=0$ and $ deg X_i=1$ for all $i$. Extend the action of $G$ on $A$ to $S$ by fixing $X_i$. Note $S^G=R$. Let $I$ be an arbitrary homogeneous ideal in $R$. The main goal of this paper is to establish a comparative study of graded components of local cohomology modules $H_I^i(R)$ that would be analogs to those proven in a previous paper of the first author for $H_J^i(S)$ where $J$ is an arbitrary homogeneous ideal in $S$.
Let $(A,mathfrak{m})$ be a local complete intersection ring and let $I$ be an ideal in $A$. Let $M, N$ be finitely generated $A$-modules. Then for $l = 0,1$, the values $depth Ext^{2i+l}_A(M, N/I^nN)$ become independent of $i, n$ for $i,n gg 0$. We also show that if $mathfrak{p}$ is a prime ideal in $A$ then the $j^{th}$ Bass numbers $mu_jbig(mathfrak{p}, Ext^{2i+l}_A(M,N/{I^nN})big)$ has polynomial growth in $(n,i)$ with rational coefficients for all sufficiently large $(n,i)$.
Let $A$ be a regular ring containing a field $K$ of characteristic zero and let $R = A[X_1,ldots, X_m]$. Consider $R$ as standard graded with $deg A = 0$ and $deg X_i = 1$ for all $i$. Let $G$ be a finite subgroup of $GL_m(A)$. Let $G$ act linearly on $R$ fixing $A$. Let $S = R^G$. In this paper we present a comprehensive study of graded components of local cohomology modules $H^i_I(S)$ where $I$ is an emph{arbitrary} homogeneous ideal in $S$. We prove stronger results when $G subseteq GL_m(K)$. Some of our results are new even in the case when $A$ is a field.
Let $A$ be a commutative Noetherian ring containing a field $K$ of characteristic zero and let $R= A[X_1, ldots, X_m]$. Consider $R$ as standard graded with $deg A=0$ and $deg X_i=1$ for all $i$. We present a few results about the behavior of the graded components of local cohomology modules $H_I^i(R)$ where $I$ is an arbitrary homogeneous ideal in $R$. We mostly restrict our attention to the Vanishing, Tameness and Rigidity problems.
Let $(R,mathfrak{m})$ be a commutative Noetherian local ring which contains a regular sequence $ underline{x} = x_1,ldots,x_d in mathfrak{m} smallsetminus mathfrak{m}^2 $ such that $ mathfrak{m}^3 subseteq (underline{x}) $. Let $ M $ be a finite $ R $-module with maximal complexity or curvature, e.g., $ M $ can be a nonzero direct summand of some syzygy module of the residue field $ R/mathfrak{m} $. It is shown that the following are equivalent: (1) $R$ is Gorenstein, (2) $mathrm{Ext}_R^{gg 0}(M,R)=0$, and (3) $mathrm{Tor}_{gg 0}^R(M,omega) = 0$, where $omega$ denotes a canonical module of $R$. It gives a partial answer to a question raised by Takahashi. Moreover, the vanishing of $mathrm{Ext}_R^{gg 0}(omega,N)$ for certain $ R $-module $ N $ is also analyzed. Finally, it is studied why Gorensteinness of such local rings is important.
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