New Lower Bounds for The Topological Complexity of Aspherical Spaces

We show that the topological complexity of an aspherical space X is bounded below by the cohomological dimension of the direct product A×BA×B, whenever A and B are subgroups of π1(X)π1(X) whose conjugates intersect trivially. For instance, this assumption is satisfied whenever A and B are complementary subgroups of π1(X)π1(X). This gives computable lower bounds for the topological complexity of many groups of interest (including semidirect products, pure braid groups, certain link groups, and Higman's acyclic four-generator group), which in some cases improve upon the standard lower bounds in terms of zero-divisors cup-length. Our results illustrate an intimate relationship between the topological complexity of an aspherical space and the subgroup structure of its fundamental group.