On powers of half-twists in M(0,2n)
arXiv:1608.08449
Abstract
We use elementary skein theory to prove a version of a result of Stylianakis who showed that under mild restrictions on m and n, the normal closure of the m-th power of a half-twist has infinite index in the mapping class group of a sphere with 2n punctures.
5 pages. v2: Reference to S. P. Humphries added in the Introduction and in Remark 3.5