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Braid forcing, hyperbolic geometry, and pseudo-Anosov sequences of low entropy


Venzke, Rupert William (2008) Braid forcing, hyperbolic geometry, and pseudo-Anosov sequences of low entropy. Dissertation (Ph.D.), California Institute of Technology.


We view braids as automorphisms of punctured disks and define a partial order on pseudo-Anosov braids called the “forcing order”. The order measures whether one automorphism induces another given automorphism on the surface. Pseudo-Anosov growth rate decreases relative to the order and appears to give a good measure of braid complexity. Unfortunately it appears difficult computationally to determine explicitly the partial order structure by hand. We use several computer algorithms to study the bottom part of the partial order when the number of braid strands is fixed. From the algorithms, we build sequences of low entropy pseudo-Anosov n-strand braids that are minimal in the sense that they do not force any other pseudo-Anosov braids on the same number of strands. The sequences are an extension of work done by Hironaka and Kin, and we conjecture the sequences to achieve minimal entropy among certain non-trivial classes of braids. In general, the lowest entropy pseudo-Anosov braids appear to have mapping tori that come from Dehn surgery on very low volume hyperbolic 3-manifolds, and we begin to analyze the relation between entropy and hyperbolic volume. Moreover, the low-growth families contain non-trivial low-growth families of horseshoe braids and we proceed to study dynamics of the horseshoe map as well.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:braid; hyperbolic geometry; pseudo-Anosov
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Mathematics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Calegari, Danny C.
Thesis Committee:
  • Calegari, Danny C. (chair)
  • Aschbacher, Michael
  • Makarov, Nikolai G.
  • Ghiggini, Paolo
Defense Date:14 May 2008
Author Email:rupert (AT)
Record Number:CaltechETD:etd-05292008-085545
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2253
Deposited By: Imported from ETD-db
Deposited On:04 Jun 2008
Last Modified:26 Dec 2012 02:49

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