Finite Products Sets and Minimally Almost Periodic Groups
We construct, in locally compact, second countable, amenable groups, sets with large density that fail to have certain combinatorial properties. For the property of being a shift of a set of measurable recurrence we show that this is possible when the group does not have cocompact von Neumann kernel. For the stronger property of being piecewise-syndetic we show that this is always possible. For minimally almost periodic, locally compact, second countable, amenable groups, we prove that any dilation of a positive density set by an open neighborhood of the identity contains a set of measurable recurrence, and that the same result holds, up to a shift, when the von Neumann kernel is cocompact. This leads to a trichotomy for locally compact, second countable, amenable groups based on combinatorial properties of large sets. We also prove, using a two-sided Furstenberg correspondence principle, that any two-sided dilation of a positive density set contains a two-sided finite products set.