Project/Area Number  10304002 
Research Category 
GrantinAid for Scientific Research (A).

Section  一般 
Research Field 
Algebra

Research Institution  KYOTO UNIVERSITY 
Principal Investigator 
MARUYAMA Masaki Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (50025459)

CoInvestigator(Kenkyūbuntansha) 
斎藤 政彦 神戸大学, 大学院・理学研究科, 教授
MORIWAKI Hiraku Kyoto Univ., Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (70191062)
吉田 敬之 京都大学, 大学院・理学研究科, 教授 (40108973)
NISHIDA Goro Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (00027377)
UENO Kenji Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (40011655)
KONO Akira Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (00093237)
深谷 賢治 京都大学, 大学院・理学研究科, 教授 (30165261)
NAKAJIMA Hiraku Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (00201666)

Project Fiscal Year 
1998 – 2000

Project Status 
Completed(Fiscal Year 2000)

Budget Amount *help 
¥23,500,000 (Direct Cost : ¥23,500,000)
Fiscal Year 2000 : ¥7,200,000 (Direct Cost : ¥7,200,000)
Fiscal Year 1999 : ¥7,600,000 (Direct Cost : ¥7,600,000)
Fiscal Year 1998 : ¥8,700,000 (Direct Cost : ¥8,700,000)

Keywords  stable vector bundle / stable sheaf / moduli / Bogomolov's inequality / reflexive sheaf / simple complex / boundedness / exceptional line / 安定ベクトル束 / 安定層 / モデュライ / ボゴモロフの不等式 / 反射的加群 / 単純な複体 / 有界性 / 第2種例外直線 / 代数的空間 / ベクトル束 / Bogomolov不等式 / 変形 / Bogomolovの不等式 
Research Abstract 
The results we have obtained are the following. 1) The curve of the jumping lines of second kind of a stable vector bundle of rank 2 on the projective plane deeply reflects the structure of the vector bundle. We found a way to determine the multiplicity and the tangent cone at a singular pint of the curve. 2) We showed a close relationship between an ordinary double point on a surface and the space of deformations of a reflexive sheaf on it. 3) We generalized Bogomolov's inequality and found an interesting relationship with the moduli space of stable curves. 4) Stable sheaves on a degenerating family of varieties were studied and gave a way to find the structure of the moduli space of stable sheaves on a nonsingular variety through a combination of simpler varieties. 5) We constructed families of surfaces on which there is a polarization such that the dimension of the moduli space of stable vector bundles is bigger than expected even for very big second Chern classes. 6) One of the subjects expected further development is the moduli space of complexes of sheaves. To get good moduli we have to give a proper definition of stable complex. Instead of this we introduced the notion of simple complex and constructed their moduli space in the category of algebraic spaces. 7) One of the most important problem is the boundedness of semistable sheaves in positive characteristic cases. In fact, this has been the main target to be solved in this project. The boundedness for a surface was proved in 1973 and for the rank 2, 3 cases in 1980 by M.Maruyama. After 20 years of no progress, we could take a step forward, that is, succeeded in proving the rank 4 case. Unfortunately the method we took cannot be generalized to higher rank cases directly and we nay have to find another way to complete the proof for general cases.
