  We obtain two types of results on positive scalar curvature metrics for
compact spin manifolds that are even dimensional. The first type of result are
obstructions to the existence of positive scalar curvature metrics on such
manifolds, expressed in terms of end-periodic eta invariants that were defined
by Mrowka-Ruberman-Saveliev (MRS). These results are the even dimensional
analogs of the results by Higson-Roe. The second type of result studies the
number of path components of the space of positive scalar curvature metrics
modulo diffeomorphism for compact spin manifolds that are even dimensional,
whenever this space is non-empty. These extend and refine certain results in
Botvinnik-Gilkey and also MRS. End-periodic analogs of K-homology and bordism
theory are defined and are utilised to prove many of our results.
