The a-function is a proposed quantity defined in even dimensions which has a
monotonic behaviour along RG flows, related to the beta-functions via a
gradient flow equation. We study the a-function for a general scalar theory in
six dimensions, using the beta-functions up to three-loop order for both the
MSbar and MOM schemes (the latter presented here for the first time at three
loops).Comment: 27 pages, seven figures, uses axodraw. Minor improvements in wordin
