Large and iterated finite group actions on manifolds admitting non-zero degree maps to nilmanifolds

Abstract: Let M be a closed connected oriented manifold admitting a non-zero degree map to a nilmanifold. In the first part of the paper we study effective finite group actions on M. In particular, we prove that Homeo(M) is Jordan, we bound the discrete degree of symmetry of M and we study the number and the size of stabilizers of an effective action of a finite group G on M. We also study the toral rank conjecture and Carlsson's conjecture for large primes for this class of manifolds. In the second part of the paper we introduce the concepts of free iterated action of groups and the iterated discrete degree of symmetry which we use to obtain cohomological rigidity results for manifolds admitting a non-zero degree map to a 2-step nilmanifold.