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arXiv 1909.07360math.GTmath.GR
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Dehn扭幂生成的环面的映射类群的子群

Subgroups of the mapping class group of the torus generated by powers of Dehn twists

Sudipta Kolay

摘要:

研究了由Dehn扭的幂生成的幂生成的环面的映射类群的子群。利用乒乓引理给出了一个判别条件,证明了幂的集合Dehn twists生成自由群.证明了由Dehn扭的三个一致幂生成的子群可以是整个映射类群,也可以是秩为2的自由群与秩为2的循环群的直积,或者是秩不超过3的自由群.我们的特点所产生的一个集合(分别平方)德恩扭曲的子群,如果有一对之间,使相应的简单闭曲线的几何相交数是两个(分别为一个)。我们还确定了所有Dehn扭转的均匀幂所生成的子群。

英文摘要:

We study subgroups of the mapping class group of the torus generated by powers generated by powers of Dehn twists. We give a criterion to show when a collection of powers Dehn twists generates a free group using the ping pong lemma. We show that the subgroup generated by three uniform powers of Dehn twists can be either the whole mapping class group, a direct product of a free group of rank two with the cyclic group of order two, or a free group of rank at most three. We characterize subgroups generated by a collection of (respectively squares of) Dehn twists, if there is a pair among so that the geometric intersection number of the corresponding simple closed curves is two (respectively one). We also determine the subgroup generated by uniform powers of all Dehn twists.

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