Representing Dehn twists with branched coverings
arXiv:0710.0102 · doi:10.1093/imrn/rnn134
Abstract
We show that any homologically non-trivial Dehn twist of a compact surface F with boundary is the lifting of a half-twist in the braid group B_n, with respect to a suitable branched covering p : F -> B^2. In particular, we allow the surface to have disconnected boundary. As a consequence, any allowable Lefschetz fibration on B^2 is a branched covering of B^2 x B^2.
Major revision. It has been added Corollary 3 about the lifting homomorphism. Are been added also some remarks and are given some other definitions. There are now 19 figures and 23 pages