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Let $K$ be a field with ${\rm char}(K)=0$. For a partition $\lambda$ of $n \in {\mathbb N}$, let $I^{\rm Sp}_\lambda$ be the ideal of $R=K[x_1,\ldots,x_n]$ generated by all Specht polynomials of shape $\lambda$. These ideals have been studied from several points of view (and under several names). Using advanced tools of the representation theory, Berkesch Zamaere et al [BGS]. constructed a minimal free resolution of $I^{\rm Sp}_{(n-d,d)}$ except differential maps. The present paper constructs the differential maps, and also gives an elementary proof of the result of [BGS]., Comment: No mathematical improvement, but exposition largely revised, especially, the title modified. 20 pages. Comments welcome

In this paper, we give the Gr��bner fan and the state polytope of a Specht ideal $I_��$ explicitly. In particular, we show that the state polytope of $I_��$ for a partition $��=(��_1, \ldots, ��_m)$ is always a generalized permutohedron, and it is a (usual) permutohedron if and only if $��_{i-1}=��_i>0$ for some $i$., 9 pages, comments welcome

For a partition $λ$ of $n$, the _Specht ideal_ $I_λ\subset K[x_1, \ldots, x_n]$ is the ideal generated by all Specht polynomials of shape $λ$. In their unpublished manuscript, Haiman and Woo showed that $I_λ$ is a radical ideal, and gave its universal Gröbner bases (recently, Murai et al. published a quick proof of this result). On the other hand, an old paper of Li and Li studied analogous ideals, while their ideals are not always radical. In the present paper, we introduce a class of ideals which generalizes both Specht ideals and _radical_ Li-Li ideals, and study their radicalness and Gröbner bases., Exposition revised, especially, Introduction extended and Lemma 3.10 added. 17 pages. Comments welcome

The Specht ideal of shape $��$, where $��$ is a partition, is the ideal generated by all Specht polynomials of shape $��$. Haiman and Woo proved that these ideals are reduced and found their universal Gr��bner bases. In this short note, we give a short proof for these results., 5 pages

Let P be a lattice polytope with $h^*$-vector $(1, h^*_1, h^*_2)$. In this note we show that if $h_2^* \leq h_1^*$, then $P$ is IDP. More generally, we show the corresponding statements for semi-standard graded Cohen-Macaulay domains over algebraically closed fields., 8 Pages

For a partition $\lambda$ of $n$, let $I^{\rm Sp}_\lambda$ be the ideal of $R=K[x_1, \ldots, x_n]$ generated by all Specht polynomials of shape $\lambda$. We show that if $R/I^{\rm Sp}_\lambda$ is Cohen--Macaulay then $\lambda$ is of the form either $(a, 1, \ldots, 1)$, $(a,b)$, or $(a,a,1)$. We also prove that the converse is true if ${\rm char}(K)=0$. To show the latter statement, the radicalness of these ideals and a result of Etingof et al. are crucial. We also remark that $R/I^{\rm Sp}_{(n-3,3)}$ is NOT Cohen--Macaulay if and only if ${\rm char}(K)=2$., Comment: 21 pages

We will define the Alexander duality for strongly stable ideals. More precisely, for a strongly stable ideal $I \subset \Bbbk[x_1, \ldots, x_n]$ with ${\rm deg}(\mathsf{m}) \le d$ for all $\mathsf{m} \in G(I)$, its dual $I^* \subset \Bbbk[y_1, \ldots, y_d]$ is a strongly stable ideal with ${\rm deg}(\mathsf{m}) \le n$ for all $\mathsf{m} \in G(I^*)$. This duality has been constructed by Fl$\o$ystad et al. in a different manner, so we emphasis applications here. For example, we will describe the Hilbert serieses of the local cohomologies $H_\mathfrak{m}^i(S/I)$ using the irreducible decomposition of $I$ (through the Betti numbers of $I^*$)., Comment: 21 pages. We clarified the proofs especially in Section 3 and added Section 6

Let $k$ be an algebraically closed field of characteristic 0, and $A$ a Cohen-Macaulay graded domain with $A_0=k$. If $A$ is semi-standard graded (i.e., $A$ is finitely generated as a $k[A_1]$-module), it has the $h$-vector $(h_0, h_1, ..., h_s)$, which encodes the Hilbert function of $A$. From now on, assume that $s=2$. It is known that if $A$ is standard graded (i.e., $A=k[A_1]$), then $A$ is level. We will show that, in the semi-standard case, if $A$ is not level, then $h_1+1$ divides $h_2$. Conversely, for any positive integers $h$ and $n$, there is a non-level $A$ with the $h$-vector $(1, h, (h+1)n)$. Moreover, such examples can be constructed as Ehrhart rings (equivalently, normal toric rings)., 12 pages

In this short note, we give a characterization of domains satisfying Serre's condition $(\mathrm{R}_1)$ in terms of their canonical modules. In the special case of toric rings, this generalizes a result of the second author (K. Yanagawa, Dualizing complexes of seminormal affine semigroup rings and toric face rings, J. Algebra 425 (2015).) where the normality is described in terms of the "shape" of the canonical module., 6 pages. Shortened exposition and improved Theorem 4.2. To appear in Comm. Alg

We give a purely combinatorial characterization of complete Stanley-Reisner rings having principally generated (equivalently, finitely generated) Cartier algebras., Comment: The main result restated in a cleaner way. 5 pages, 2 figures. To appear in J. Algebra

The notion of "toric face rings" generalizes both Stanley-Reisner rings and affine semigroup rings, and has been studied by Bruns, Romer, et.al. Here, we will show that, for a toric face ring $R$, the "graded" Matlis dual of a Cech complex gives a dualizing complex. In the most general setting, $R$ is not a graded ring in the usual sense. Hence technical argument is required.

Let $C \subset {\bf N}^d$ be an affine semigroup, and $R=K[C]$ its semigroup ring. This paper is a collection of various results on "$C$-graded" $R$-modules, especially, monomial ideals. For example, we show the following: If $R$ is normal and $I$ is a radical monomial ideal (i.e., $R/I$ is a generalization of Stanley-Reisner rings), then the sequentially Cohen-Macaulay property of $R/I$ is a topological property of the "geometric realization" of the cell complex associated with $I$. Moreover, we can give a squarefree modules/constructible sheaves version of this result., LARGELY revised version. Sections 4, 5 and most of section 3 are new. 23 pages

Let A be a noetherian AS regular Koszul quiver algebra (if A is commutative, it is essentially a polynomial ring), and grA the category of finitely generated graded left A-modules. Following Jorgensen, we define the Castelnuovo-Mumford regularity reg(X) of a complex X \in D^b(grA) in terms of the local cohomologies or the minimal projective resolution of X. Let A^! be the quadratic dual ring of A. For the Koszul duality functor DG : D^b(grA) -> D^b(grA^!), we have reg(X) = max {i | H^i(DG (X)) \ne 0}. Using these concepts, we study weakly Koszul modules (= componentwise linear modules) over A^!. As an application, refining a result of Herzog and Roemer, we show that if J is a monomial ideal of an exterior algebra E= \bigwedge < y_1, ..., y_d > with d \geq 3, then the (d-2)nd syzygy of E/J is weakly Koszul., 21 pages, to appear in J. Pure Appl. Algebra, the description of the "(non-commutative)canonical module" is corrected

Let E = K< y_1, ..., y_n > be the exterior algebra. The ``(cohomological) distinguished pairs" of a graded E-module M describe the growth of a minimal graded injective resolution of M. Roemer gave a duality theorem between the distinguished pairs of M and those of its dual M^*. In this paper, we show that under Bernstein-Gel'fand-Gel'fand correspondence, his theorem is translated into a natural corollary of local duality for (complexes of) graded S=K[x_1, >..., x_n]-modules. Using this idea, we also give a Z^n-graded version of Roemer's theorem., 11 pages. To appear in Algebras and Representation Theory