Braid groups, mapping class groups, and Torelli groups

Stylianakis, Charalampos (2016) Braid groups, mapping class groups, and Torelli groups. PhD thesis, University of Glasgow.

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This thesis discusses subgroups of mapping class groups of particular surfaces. First, we study the Torelli group, that is, the subgroup of the mapping class group that acts trivially on the first homology. We investigate generators of the Torelli group, and we give an algorithm that factorizes elements of the Torelli group into products of particular generators.

Furthermore, we investigate normal closures of powers of standard generators of the mapping class group of a punctured sphere. By using the Jones representation, we prove that in most cases these normal closures have infinite index in the mapping class group. We prove a similar result for the hyperelliptic mapping class group, that is, the group that consists of mapping classes that commute with a fixed hyperelliptic involution. As a corollary, we recover an older theorem of Coxeter (with 2 exceptional cases), which states that the normal closure of the m-th power of standard generators of the braid group has infinite index in the braid group.

Finally, we study finite index subgroups of braid groups, namely, congruence subgroups of braid groups. We discuss presentations of these groups and we provide a topological interpretation of their generating sets.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QA Mathematics
Colleges/Schools: College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Supervisor's Name: Brendle, Prof. Tara
Date of Award: 2016
Depositing User: Charalampos Stylianakis
Unique ID: glathesis:2016-7466
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jul 2016 07:42
Last Modified: 27 Jul 2016 10:03

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