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FRACTIONAL POWERS OF DEHN TWISTS ABOUT NONSEPARATING CURVES

Published online by Cambridge University Press:  02 September 2013

KASHYAP RAJEEVSARATHY
KASHYAP RAJEEVSARATHY*
Affiliation:
Department of Mathematics, Indian Institute of Science Education Research Bhopal, ITI (Gas Rahat) Building, Govindpura, Bhopal 462023, Madhya Pradesh, India e-mail: [email protected]
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Abstract

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Let Sg be a closed orientable surface of genus g ≥ 2 and C a simple closed nonseparating curve in F. Let tC denote a left-handed Dehn twist about C. A fractional power of tC of exponent ℓ//n is an h ∈ Mod(Sg) such that hn = tCℓ. Unlike a root of a tC, a fractional power h can exchange the sides of C. We derive necessary and sufficient conditions for the existence of both side-exchanging and side-preserving fractional powers. We show in the side-preserving case that if gcd(ℓ,n) = 1, then h will be isotopic to the ℓth power of an nth root of tC and that n ≤ 2g+1. In general, we show that n ≤ 4g, and that side-preserving fractional powers of exponents 2g//2g+2 and 2g//4g always exist. For a side-exchanging fractional power of exponent ℓ//2n, we show that 2n ≥ 2g+2, and that side-exchanging fractional powers of exponent 2g+2//4g+2 and 4g+1//4g+2 always exist. We give a complete listing of certain side-preserving and side-exchanging fractional powers on S5.

Keywords

57M9957M60
Type
Research Article
Information
Glasgow Mathematical Journal , Volume 56 , Issue 1 , January 2014 , pp. 197 - 210
Copyright
Copyright © Glasgow Mathematical Journal Trust 2013 

References

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