Browsing by Author "Putman, Thomas Andrew"

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    The large scale geometry of strongly aperiodic subshifts of finite type
    (2015-04-22) Cohen, David Bruce; Putman, Thomas Andrew; Cox, Steven J; Veech, William A
    A subshift on a group G is a closed, G-invariant subset of A to the G, for some finite set A. It is said to be of finite type if it is defined by a finite collection of “forbidden patterns” and to be strongly aperiodic if it has no points fixed by a nontrivial element of the group. We show that if G has at least two ends, then there are no strongly aperiodic subshifts of finite type on G (as was previously known for free groups). Additionally, we show that among torsion free, finitely presented groups, the property of having a strongly aperiodic subshift of finite type is invariant under quasi isometry.
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    Two mod-p Johnson filtrations
    (2014-04-17) Cooper, James Michael; Putman, Thomas Andrew; Wolf, Michael; Hicks, Illya V.
    We consider two mod-p central series of the free group given by Stallings and Zassenhaus. Applying these series to definitions of Dennis Johnson's filtration of the mapping class group we obtain two mod-p Johnson filtrations. Further, we adapt the definition of the Johnson homomorphisms to obtain mod-p Johnson homomorphisms. We calculate the image of the first of these homomorphisms. We give generators for the kernels of these homomorphisms as well. We restrict the range of our mod-p Johnson homomorphisms using work of Morita. We finally prove the announced result of Perron that a rational homology 3-sphere may be given as a Heegaard splitting with gluing map coming from certain members of our mod-p Johnson filtrations.