Out(F3) Index Realization

2015 ◽  
Vol 159 (3) ◽  
pp. 445-458 ◽  
Author(s):  
CATHERINE PFAFF
Keyword(s):  
Free Group ◽  
Quadratic Differentials ◽  
Singularity Index ◽  
Outer Automorphisms ◽  
Teichmüller Flow ◽  
Surface Homeomorphism

AbstractBy proving precisely which singularity index lists arise from the pair of invariant foliations for a pseudo-Anosov surface homeomorphism, Masur and Smillie [MS93] determined a Teichmüller flow invariant stratification of the space of quadratic differentials. In this paper we determine an analog to the theorem forOut(F3). That is, we determine which index lists permitted by the [GJLL98] index sum inequality are achieved by ageometric fully irreducible outer automorphisms of the rank-3 free group.

scholarly journals Ideal Whitehead graphs in Out(Fr) III: Achieved graphs in rank 3

2016 ◽  
Vol 08 (02) ◽  
pp. 207-242 ◽  
Author(s):  
Catherine Pfaff
Keyword(s):  
Direct Consequence ◽  
Quadratic Differentials ◽  
Text Setting ◽  
Singularity Index ◽  
Outer Automorphisms ◽  
Analogous Formula ◽  
Surface Homeomorphisms ◽  
Rank 2 ◽  
Surface Homeomorphism ◽  
The Ideal

By proving precisely which singularity index lists arise from the pair of invariant foliations for a pseudo-Anosov surface homeomorphism, Masur and Smillie [24] determined a Teichmüller flow invariant stratification of the space of quadratic differentials. In this final paper of a three-paper series, we give a first step to an [Formula: see text] analog of the Masur–Smillie theorem. Since the ideal Whitehead graphs defined by Handel and Mosher [16] give a strictly finer invariant in the analogous [Formula: see text] setting, we determine which of the 21 connected, simplicial, five-vertex graphs are ideal Whitehead graphs of fully irreducible outer automorphisms in [Formula: see text]. The rank 2 case is actually a direct consequence of the work of Masur and Smillie, as all elements of [Formula: see text] are induced by surface homeomorphisms and the index list and ideal Whitehead graph for a surface homeomorphism give precisely the same data.

scholarly journals AN EQUIVARIANT WHITEHEAD ALGORITHM AND CONJUGACY FOR ROOTS OF DEHN TWIST AUTOMORPHISMS

2001 ◽  
Vol 44 (1) ◽  
pp. 117-141 ◽  
Author(s):  
Sava Krstić ◽  
Martin Lustig ◽  
Karen Vogtmann
Keyword(s):  
Free Group ◽  
Finite Groups ◽  
Linear Growth ◽  
Conjugacy Problem ◽  
Dehn Twist ◽  
Subject Classification ◽  
Finitely Generated ◽  
Finite Sets ◽  
Outer Automorphisms ◽  
Secondary 57M07

AbstractGiven finite sets of cyclic words $\{u_1,\dots,u_k\}$ and $\{v_1,\dots,v_k\}$ in a finitely generated free group $F$ and two finite groups $A$ and $B$ of outer automorphisms of $F$, we produce an algorithm to decide whether there is an automorphism which conjugates $A$ to $B$ and takes $u_i$ to $v_i$ for each $i$. If $A$ and $B$ are trivial, this is the classic algorithm due to Whitehead. We use this algorithm together with Cohen and Lustig’s solution to the conjugacy problem for Dehn twist automorphisms of $F$ to solve the conjugacy problem for outer automorphisms which have a power which is a Dehn twist. This settles the conjugacy problem for all automorphisms of $F$ which have linear growth.AMS 2000 Mathematics subject classification: Primary 20F32. Secondary 57M07

scholarly journals Local structure of some Out(Fn)-complexes

1990 ◽  
Vol 33 (3) ◽  
pp. 367-379 ◽  
Author(s):  
Karen Vogtmann
Keyword(s):  
Free Group ◽  
Finite Rank ◽  
Local Structure ◽  
Simplicial Complexes ◽  
Homotopy Equivalent ◽  
Outer Automorphisms ◽  
Finite Quotient

In previous work of the author and M. Culler, contractible simplicial complexes were constructed on which the group of outer automorphisms of a free group of finite rank acts with finite stabilizers and finite quotient. In this paper, it is shown that these complexes are Cohen-Macauley, a property they share with buildings. In particular, the link of a vertex in these complexes is homotopy equivalent to a wedge of spheres of codimension 1.

scholarly journals Irreducible outer automorphisms of a free group

1991 ◽  
Vol 111 (2) ◽  
pp. 309-309 ◽  
Author(s):  
S. M. Gersten ◽  
J. R. Stallings
Keyword(s):  
Free Group ◽  
Outer Automorphisms

Teichmuller Geometry

2017 ◽  
Author(s):  
Benson Farb ◽  
Dan Margalit
Keyword(s):  
Uniqueness Theorem ◽  
Existence Theorems ◽  
Quadratic Differentials ◽  
Complex Structures ◽  
Metric Geometry ◽  
Quasiconformal Maps ◽  
Hyperbolic Structures ◽  
Teichmüller Metric ◽  
Uniqueness And Existence ◽  
Teichmüller Mapping

This chapter focuses on the metric geometry of Teichmüller space. It first explains how one can think of Teich(Sɡ) as the space of complex structures on Sɡ. To this end, the chapter defines quasiconformal maps between surfaces and presents a solution to the resulting Teichmüller's extremal problem. It also considers the correspondence between complex structures and hyperbolic structures, along with the Teichmüller mapping, Teichmüller metric, and the proof of Teichmüller's uniqueness and existence theorems. The fundamental connection between Teichmüller's theorems, holomorphic quadratic differentials, and measured foliations is discussed as well. Finally, the chapter describes the Grötzsch's problem, whose solution is tied to the proof of Teichmüller's uniqueness theorem.

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