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ROOTS OF DEHN TWISTS ABOUT MULTICURVES

Published online by Cambridge University Press:  30 October 2017

KASHYAP RAJEEVSARATHY
Affiliation:
Department of Mathematics, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhauri, Bhopal 462066, Madhya Pradesh, India e-mail: kashyap@iiserb.ac.in (https://home.iiserb.ac.in/ekashyap/), prahlad@iiserb.ac.in (https://home.iiserb.ac.in/eprahlad/)
PRAHLAD VAIDYANATHAN
Affiliation:
Department of Mathematics, Indian Institute of Science Education and Research Bhopal, Bhopal Bypass Road, Bhauri, Bhopal 462066, Madhya Pradesh, India e-mail: kashyap@iiserb.ac.in (https://home.iiserb.ac.in/ekashyap/), prahlad@iiserb.ac.in (https://home.iiserb.ac.in/eprahlad/)
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Abstract

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A multicurve${\mathcal{C}}$ in a closed orientable surface Sg of genus g is defined to be a finite collection of disjoint non-isotopic essential simple closed curves. A left-handed Dehn twist$t_{\mathcal{C}}$about${\mathcal{C}}$ is the product of left-handed Dehn twists about the individual curves in ${\mathcal{C}}$. In this paper, we derive necessary and sufficient conditions for the existence of a root of $t_{\mathcal{C}}$ in the mapping class group Mod(Sg). Using these conditions, we obtain combinatorial data that correspond to roots, and use it to determine upper bounds on the degree of a root. As an application of our theory, we classify all such roots up to conjugacy in Mod(S4). Finally, we establish that no such root can lie in the level m congruence subgroup of Mod(Sg), for m ≥ 3.

Type
Research Article
Copyright
Copyright © Glasgow Mathematical Journal Trust 2017 

References

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