Time: 2018.10.09, 15:00–17:00
Location: Seminarraum 8, Oskar-Morgenstern-Platz 1, 2.Stock
Title: "Cogrowth for group actions with a strongly contracting element."
Speaker: Christopher Cashen (Universität Wien)
Abstract: We show that for a finitely generated group $$G$$ acting properly on a geodesic metric space $$X$$ with a strongly contracting element and purely exponential growth, and for every infinite normal subgroup $$N$$ of $$G$$, the growth rates $$\delta_G$$ and $$\delta_N$$ of the orbits of $$G$$ and $$N$$ in $$X$$ satisfy $$\delta_N/\delta_G > 1/2$$. This generalizes several results where the same conclusion is obtained for $$G$$ a free group or $$X$$ a negatively curved space. This is joint work with Arzhantseva.