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トポロジー火曜セミナー

過去の記録 ~06/25次回の予定今後の予定 06/26~

開催情報 火曜日 17:00~18:30 数理科学研究科棟(駒場) 056号室
担当者 河澄 響矢, 北山 貴裕, 逆井卓也, 葉廣和夫
セミナーURL https://park.itc.u-tokyo.ac.jp/MSF/topology/TuesdaySeminar/index.html

2007年01月23日(火)

16:30-18:30   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
中田 文憲 氏 (東京大学大学院数理科学研究科) 16:30-17:30
The twistor correspondence for self-dual Zollfrei metrics
----their singularities and reduction

[ 講演概要 ]
C. LeBrun and L. J. Mason investigated a twistor-type correspondence
between indefinite conformal structures of signature (2,2) with some properties
and totally real embeddings from RP^3 to CP^3.
In this talk, two themes following LeBrun and Mason are explained.

First we consider an additional structure:
the conformal structure is equipped with a null surface foliation
which has some singularity.
We establish a global twistor correspondence for such structures,
and we show that a low dimensional correspondence
between some quotient spaces is induced from this twistor correspondence.

Next we formulate a certain singularity for the conformal structures.
We generalize the formulation of LeBrun and Mason's theorem
admitting the singularity, and we show explicit examples.

大橋 了 氏 (東京大学大学院数理科学研究科) 17:30-18:30
On the homology group of Out(Fn)
[ 講演概要 ]
Suppose Fn is the free group of rank n,
Out(Fn)=Aut(Fn)/Inn(Fn) the outer automorphism group of Fn.
We compute H(Out(Fn);mathbbQ) for nleq6 and conclude
that non-trivial classes in this range are generated
by Morita classes muiinH4i(Out(F2i+2);mathbbQ).
Also we compute odd primary part of H(Out(F4);mathbbZ).