V. A. Iskovskikh
I give a survey of Noether-Fano inequalities in birational geometry, starting with the original Noether inequality and up to the modern approach of Log Minimal Model program. The paper is based on my talk at the Fano conference in Torino in October 2002. This is the revised version: an erroneous reference in my paper published in the Proceedings of Fano conference is corrected.
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We prove a more general and precise version of the Noether-Fano inequalities for birational maps between Mori fiber spaces. This is applied to give descriptions of global canonical thresholds on Fano varieties of Picard number one.
Mukai bundles and Brill-Noether generality for prime Fano threefolds in positive characteristic
针对正特征下亏格≥8的素法诺三维簇，证明其存在对应亏格非平凡分解的唯一向井丛，核心方法是证明其光滑超平面截面为布里尔-诺特一般，丰富了代数几何中相关簇的结构理论。
Brill-Noether reconstruction of index one prime Fano threefolds
本文通过统一论证表明，每个亏格g≥6的指数一素Fano三维簇X可以作为Kuznetsov分量Ku(X)中Bridgeland模空间稳定对象的Brill-Noether轨迹重构，并验证了Mukai对偶嵌入猜想，建立了精细的分类Torelli定理，分类了Ku(X)的自等价，并给出了Kuznetsov Fano三维簇猜想的另一种否证。
Density of Noether-Lefschetz loci for surfaces in Fano and Calabi-Yau threefolds
该研究利用 Hodge 轨迹的一般定理，考察 Fano 与 Calabi–Yau 三维簇中充分丰富线性系统曲面族的 Noether–Lefschetz 轨迹，并比较一般分支与例外分支并集的不同密度行为。
Given a smooth prime Fano threefold $X$ of genus 7 we consider its homologically projectively dual curve $Γ$ and the natural integral functor $Φ^{!}:D^b(X) \to D^b(Γ)$. We prove that, for $d\geq 6$, $Φ^{!}$ gives a birational map from a component of the moduli scheme $M_X(2,1,d)$ of rank 2 stable sheaves on $X$ with $c_1=1$, $c_2=d$ to a generically smooth $2d-9$-dimensional component of the Brill-Noether variety $W^{2d-11}_{d-5,5d-24}$ of stable vector bundles on $Γ$ of rank $d-5$ and degree $5d-24$ with at least $2d-10$ sections. This map turns out to be an isomorphism for $d=6$, and the mod…
A Brill-Noether locus is a subscheme of the moduli of bundles E over a curve C defined by requiring E to have a given number of sections, or homomorphisms from another bundle. There are a number of different types, that can be treated by determinantal methods, with symmetry or skewsymmetry arising from Serre duality. They have many beautiful applications to curves, K3 surfaces and Fano 3-folds.
We modify the conjectural Bogomolov-Gieseker type inequality introduced by Bayer, Macri and Toda to construct a family of geometric Bridgeland stability conditions on smooth projective 3-folds. We give an equivalent conjecture which needs to check these inequalities for a small class of tilt stable objects. We extend some of the techniques in Li's work for Fano 3-folds of Picard rank one to establish our modified Bogomolov-Gieseker type inequality conjecture for general Fano 3-folds.
If $X$ is a smooth complex projective 3-fold with ample canonical divisor $K$, then the inequality $K^3\ge {2/3}(2p_g-7)$ holds, where $p_g$ denotes the geometric genus. This inequality is nearly sharp. We also give similar, but more complicated, inequalities for general minimal 3-folds of general type. (A noether type of inequality lies, by all means, on the other side of the Miyaoka-Yau inequality from the geographical point of view.)
We develop a framework to modify the Bogomolov-Gieseker type inequality conjecture introduced by Bayer-Macri-Toda, in order to construct a family of geometric Bridgeland stability conditions on any smooth projective 3-fold. We show that it is enough to check these modified inequalities on a small class of tilt stable objects. We extend some of the techniques in the works by Li and Bernardara-Macri-Schmidt-Zhao to formulate a strong form of Bogomolov-Gieseker inequality for tilt stable objects on Fano 3-folds. Consequently, we establish our modified Bogomolov-Gieseker type inequality conjecture…
A birational transformation of three-dimensional quadric is constructed. The inequalities of fano are not fulfilled for this transformation.
Noether-type inequalities for big divisors via control of the negative part
本文研究了光滑射影表面中大除子的体积与零维数的关系，引入了一个仅依赖负部分的数值不变量，从而建立了Noether型不等式，并应用于adjoint divisors和foliations。
Determining when the birational automorphism group of a Fano variety is finite is an interesting and difficult problem. The main technique for studying this problem is by the Noether-Fano method. This method has been effective in studying this problem for Fano varieties of index one and two. The purpose of this paper is to give a new approach to this problem, and to show that in every positive characteristic there are Fano varieties of arbitrarily large index with finite (or even trivial) birational automorphisms. To do this we prove that these varieties admit ample and birationally equivarian…
By a result of Mukai, the non-abelian Brill-Noether locus X = M_C(2,K:3F) of type II, defined by a stable rank 2 vector bundle F of invariant 3 over a plane quartic curve C, is a prime Fano 3-fold X of degree 16. The associate ruled surface S^X = P(F) is uniquely defined by X, and we see that for the general X = X_{16}, S^X is isomorphic to the Fano surface of conics on X. The argument uses the geometry of the Sp_3-grassmannian and the double projection from a line on X_{16}.
Sharp Noether-type inequalities for $3$-folds of intermediate Kodaira dimensions
本文针对中间小平维数的光滑射影三维流形，建立了尖锐的 Noether 型不等式，给出了伊塔卡体积与几何亏格的下界关系，并刻画了等号成立的条件。
Let $X$ be a nonsingular projective $n$-fold $(n\ge 2)$ of Fano or of general type with ample canonical bundle $K_X$ over an algebraic closed field $κ$ of any characteristic. We produce a new method to give a bunch of inequalities in terms of all the Chern classes $c_1, c_2, \cdots, c_n$ by pulling back Schubert classes in the Chow group of Grassmannian under the Gauss map. Moreover, we show that if the characteristic of $κ$ is $0$, then the Chern ratios $(\frac{c_{2,1^{n-2}}}{c_{1^n}}, \frac{c_{2,2,1^{n-4}}}{c_{1^n}}, \cdots, \frac{c_{n}}{c_{1^n}})$ are contained in a convex polyhedron for al…
Reverse Hölder inequalities on the space of Kähler metrics of a Fano variety and effective openness
本文在Fano流形Kähler度量空间上建立反向Hölder不等式，利用隐藏对数凹性证明并推广至对数终端奇点Fano簇，进而得到测地线速度不等式、有效开性结果及与Igusa zeta函数的联系。
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