Ken-ichi Yoshida

activity

20242026

collaborators

11 papers

math.AC2026

Nearly Gorenstein normal graded rings

Tomohiro Okuma, Kei-ichi Watanabe, Ken-ichi Yoshida

We investigate nearly Gorenstein property for a normal graded ring $R = ⨁_{n \geq 0} R_{n}$ finitely generated over a field. For that purpose, we investigate $K_{R}^{- 1}$ , the i…

math.AG2025

A variant of R{ö}hr's vanishing theorem with an application to the normal reduction number for normal surface singularities

Tomohiro Okuma, Kei-ichi Watanabe, Ken-ichi Yoshida

Let $A$ be an excellent two-dimensional normal local ring containing an algebraically closed field and let $X \to Spec (A)$ be a resolution of singularity. We prove a theor…

math.AG2025

Nearly Gorenstein rational surface singularities

Kyosuke Maeda, Tomohiro Okuma, Kei-ichi Watanabe +1

In this paper, we show that for any rational surface singularity $A$ , the canonical trace ideal $Tr_{A} (K_{A})$ is an integrally closed ideal, which is represented by the mini…

math.AC2025

Gorenstein Normal tangent cones of integrally closed ideals in two-dimensional normal singularities

Tomohiro Okuma, Kei-ichi Watanabe, Ken-ichi Yoshida

Let $(A, m)$ be a two-dimensional excellent normal Gorenstein local domain containing an algebraically closed filed. Let $I = H^{0} (X, O_{X} (- Z)) \subset A$ be an $\ma…

math.AC2025

Hilbert-Kunz multiplicity of quadrics via Ehrhart theory

Igor Pak, Boris Shapiro, Ilya Smirnov +1

We show that the Hilbert-Kunz multiplicity of the d-dimensional non-degenerate quadric hypersurface of characteristic p > 2 is a rational function of p composed from the Ehrhart po…

math.AC2025

Ulrich ideals on rational triple points of dimension two

Kyosuke Maeda, Ken-ichi Yoshida

In this paper, we prove the canonical trace ideal trace(omega_A) is an Ulrich ideal for any two-dimensional rational triple point A. Using this, we classify all Ulrich ideals on ra…

math.GT2025

Uniqueness of free 2-periodicities of links

Ken'ichi Yoshida

We show that if two links in the real projective 3-space $RP^{3}$ have isotopic preimages in the 3-sphere $S^{3}$ by the double covering map, then they are themselves isot…

math.AC2024

A Geometric description of almost Gorensteinness for two-dimensional normal singularities

Tomohiro Okuma, Kei-ichi Watanabe, Ken-ichi Yoshida

Let $A$ be an excellent two-dimensional normal local ring containing an algebraically closed field. Then $A$ is called an elliptic singularity if $p_{f} (A) = 1$ , where $p_{f}$ denotes th…

math.AG2024

On vanishing of higher direct images of the structure sheaf

Shihoko Ishii, Ken-ichi Yoshida

We show the vanishing of the first direct image of the structure sheaf of a normal scheme $X$ which is mapped properly and birationally over a regular scheme of any dimension. On t…

math.GT2024

Links in the spherical 3-manifold obtained from the quaternion group and their lifts

Ken'ichi Yoshida

We show that there are infinitely many triples of non-isotopic hyperbolic links in the lens space $L (4, 1)$ such that the three lifts of each triple in $S^{3}$ are isotopic. They ar…

math.AC2024

On Gorensteinness of associated graded rings of filtrations

Meghana Bhat, Saipriya Dubey, Shreedevi K. Masuti +4

Let $(A, m)$ be a Gorenstein local ring, and $F = {F_{n}}_{n \in Z}$ a Hilbert filtration. In this paper, we give a criterion for Gorensteinness of the…