TY - JOUR TI - Constructing and classifying fully irreducible outer automorphisms of free groups DO - https://doi.org/doi:10.7282/T30R9N56 PY - 2012 AB - The main theorem of this document emulates, in the context of Out(F_r) theory, a mapping class group theorem (by H. Masur and J. Smillie) that determines precisely which index lists arise from pseudo-Anosov mapping classes. Since the ideal Whitehead graph gives a finer invariant in the analogous setting of a fully irreducible outer automorphisms of free groups, we instead focus on determining which of the twenty-one connected, loop-free, five-vertex graphs are ideal Whitehead graphs of ageometric, fully irreducible outer automorphisms of free groups in rank three. Our main theorem accomplishes this by showing that there are precisely eighteen graphs arising as such. We also give a method for identifying certain complications called periodic Nielsen paths, prove the existence of conveniently decomposed representatives of ageometric, fully irreducible outer automorphisms of free groups having connected, (2r-1)-vertex ideal Whitehead graphs, and prove a criterion for identifying representatives of ageometric, fully irreducible outer automorphisms of free groups. The strategies we use for constructing fully irreducible outer automorphisms of free groups, as well as our identification and decomposition techniques, can be used to extend our main theorem, as they are valid in any rank. Our methods of proof rely primarily on Bestvina-Feighn-Handel train track theory and the theory of attracting laminations. KW - Mathematics KW - Geometric group theory LA - eng ER -