# トポロジーセミナー (10月31日)

日時: ２０１３年１０月３１日（木）１６：００－１７：３０

場所: 筑波大学 自然系学系Ｄ棟 Ｄ５０９

講演者: 金英子 氏 （大阪大学 理学研究科）

講演題目: Pseudo-Anosovs with small dilatations coming from the magic 3-manifold

アブストラクト:

Pseudo-Anosov mapping classes are equipped with some constants >1 called the dilatation. It is known that the logarithm of the dilatation is exactly equal to the topological entropy of a pseudo-Anosov representative of its mapping class. By work of Thurston, if a hyperbolic fibered 3-manifold M has the second Betti number more than 1, then it admits infinitely many fibrations on M. Moreover the monodromy of any fibration on M is pseudo-Anosov. As an example of such manifolds, we consider a single 3-manifold N with 3 cusps called the magic 3-manifold. We compute the dilatation of monodromy of each fibration on N. We also discuss the problem on the minimal dilatations and their asymptotic behavior. Intriguingly, pseudo-Anosovs with the smallest known dilatations are ``coming from" the magic 3-manifold. This is a joint work with Mitsuhiko Takasawa.