Transcendence of some Hilbert-Kunz multiplicities (modulo a conjecture)

Algebraicity of some Hilbert-Kunz multiplicities (modulo a conjecture)

Let F be a finite field of characteristic 2 and h be the element x^3+y^3+xyz of F[[x,y,z]]. In an earlier paper we made a precise conjecture as to the values of the colengths of the ideals (x^q,y^q,z^q,h^j) for q a power of 2. We also showed that if the conjecture holds then the Hilbert-Kunz series of H=uv+h is algebraic (of degree 2) over Q(w), and that mu(h) is algebraic (explicitly, (4/3)+(5/14)sqrt(7)). In this note, assuming the same conjecture, we use a theory of infinite matrices to rederive this result, and we extend it to a wider class of H; for example H=g(u,v)+h. In a follow-up pape…

Irrational Hilbert-Kunz multiplicities

We interpret Hilbert-Kunz theory of a graded ring of positive characteristic in terms of Frobenius asymptotic of cohomology of vector bundles on projective varieties. With this method we show that for almost all prime numbers there exist three-dimensional quartic hypersurface domains and modules of finite length with irrational Hilbert-Kunz multiplicity. From this we deduce that also the Hilbert-Kunz multiplicity of a local noetherian domain might be an irrational number.

Notes on Hilbert-Kunz multiplicity of Rees algebras

In this paper, we estimate the Hilbert-Kunz multiplicity of the (extended) Rees algebras in terms of some invariants of the base ring. Also, we give an explicit formula for the Hilbert-Kunz multiplicities of Rees algebras over Veronese subrings.

Lower bounds on Hilbert--Kunz multiplicities and maximal F-signatures

Hilbert-Kunz multiplicity and F-signature are numerical invariants of commutative rings in positive characteristic that measure severity of singularities: for a regular ring both invariants are equal to one and the converse holds under mild assumptions. A natural question is for what singular rings these invariants are closest to one. For Hilbert--Kunz multiplicity this question was first considered by the last two authors and attracted significant attention. In this paper, we study this question, i.e., an upper bound, for F-signature and revisit lower bounds on Hilbert--Kunz multiplicity.

超越希尔伯特-孔兹重数

Transcendental Hilbert-Kunz Multiplicities

该研究证明普通希尔伯特-孔兹重数可呈超越性，在特征p>2的不可数代数闭域上构造出满足对应超越性条件的正规分次整环及相关理想。

Semistability and Hilbert-Kunz multiplicities for curves

We study Hilbert-Kunz multiplicity of non-singular curves in positive characteristic. We analyse the relationship between the Frobenius semistability of the kernel sheaf associated with the curve and its ample line bundle, and the HK multiplicity. This leads to a lower bound, achieved iff the kernel sheaf is Frobenius semistable, and otherwise to formulas for the HK multiplicity in terms of parameters measuring the failure of Frobenius semistability. As a byproduct, an explicit example of a vector bundle on a curve is given whose $n$-th iterated Frobenius pullback is not semistable, while its …

理想族的广义Hilbert-Kunz重数

Generalized Hilbert-Kunz Multiplicity for Families of Ideals

本文系统研究正特征Noetherian局部环中理想族的广义Hilbert-Kunz重数，引入Amao型重数这一新渐近不变量，证明p-理想族的广义Hilbert-Kunz重数是Amao型重数的极限。

On semicontinuity of multiplicities in families

The paper investigates the behavior of Hilbert-Samuel and Hilbert-Kunz multiplicities in families of ideals. It is shown that Hilbert-Samuel multiplicity is upper semicontinuous almost generally and that Hilbert-Kunz multiplicity is upper semicontinuous in families of finite type. Surprisingly, our machinery can be applied for families over Z and yields a partial solution to the question about characteristic zero Hilbert-Kunz multiplicity posed by Brenner, Li, and Miller. Another application is that for an affine ring the infimum in the definition of F-rational signature, an invariant defined …

奇异环的Hilbert-Kunz重数的界

Bounds for the Hilbert-Kunz Multiplicity of Singular Rings

本文通过引入插值函数$\varphi_J$并证明其凹性，结合已知技术得到改进下界，从而证明了Watanabe-Yoshida猜想在维数至多$7$时成立。

Hilbert-Kunz multiplicity and reduction mod p

We show that the Hilbert-Kunz multiplicities of the reductions to positive characteristics of an irreducible projective curve in characteristic 0 have a well-defined limit as the characteristic tends to infinity.

Hilbert-Kunz multiplicity of three-dimensional local rings

In this paper, we investigate a lower bound (say $s_{HK}(p,d)$) on Hilbert-Kunz multiplicities for non-regular unmixed local rings of Krull dimension $d$ with characteristic $p>0$. Especially, we focus three-dimensional local rings. In fact, as a main result, we will prove that $s_{HK}(p,3) = 4/3$ and that a three-dimensional complete local ring of Hilbert-Kunz multiplicity 4/3 is isomorphic to the non-degnerate quadric hyperplanes $k[[X,Y,Z,W]]/(X^2+Y^2+Z^2+W^2)$ under mild conditions. Furthermore, we pose a generalization of the main theorem to the case of $\dim A \ge 4$ as a conjecture, and…

On Lower Bounds for $s$-multiplicities

A recent continuous family of multiplicity functions on local rings was introduced by Taylor interpolating between Hilbert-Samuel and Hilbert-Kunz multiplicities. The obvious goal is to use this as a tool for deforming results from one to the other. The values in this family which do not match these classic variants however are not known yet to be well-behaved. This article explores lower bounds for these intermediate multiplicities as well as gives evidence for analogies of the Watanabe-Yoshida minimality conjectures for unmixed singular rings.

Hilbert-Kunz Multiplicity of Fibers and Bertini Theorems

Let $k$ be an algebraically closed field of characteristic $p > 0$. We show that if $X\subseteq\mathbb{P}^n_k$ is an equidimensional subscheme with Hilbert--Kunz multiplicity less than $λ$ at all points $x\in X$, then for a general hyperplane $H\subseteq\mathbb{P}^n_k$, the Hilbert--Kunz multiplicity of $X\cap H$ is less than $λ$ at all points $x\in X\cap H$. This answers a conjecture and generalizes a result of Carvajal-Rojas, Schwede and Tucker, whose conclusion is the same as ours when $X\subseteq\mathbb{P}^n_k$ is normal. In the process, we substantially generalize certain uniform estimate…

简单奇点与费马超曲面的极限F-不变量

Limit F-invariants of the simple singularities and the Fermat hypersurfaces

本文计算了简单奇点与费马超曲面的极限F-不变量，推广了相关公式，并将正则环刻画与Watanabe--Yoshida猜想推广至特征零。

The lower bound on the HK multiplicities of quadric hypersurfaces

Here we prove that the Hilbert-Kunz mulitiplicity of a quadric hypersurface of dimension $d$ and odd characteristic $p\geq 2d-4$ is bounded below by $1+m_d$, where $m_d$ is the $d^{th}$ coefficient in the expansion of $\mbox{sec}+\mbox{tan}$. This proves a part of the long standing conjecture of Watanabe-Yoshida. We also give an upper bound on the HK multiplicity of such a hypersurface. We approach the question using the HK density function and the classification of ACM bundles on the smooth quadrics via matrix factorizations.