DTC ultrafilters on groups

Semigroup Forum - We say that an ultrafilter on an infinite group G is DTC if it determines the topological centre of the semigroup $$\beta G$$ . If G has a subgroup of finite index in which...     

Measurable centres in convolution semigroups

In certain convolution semigroups over locally compact groups, the only measurable translations are those defined by Radon measures. In other words, the measurable centre of every such convolution semigroup consists of Radon measures.     

Ambitable topological groups

A topological group is said to be ambitable if every uniformly bounded uniformly equicontinuous set of functions on the group with its right uniformity is contained in an ambit. For n=0,1,2,… , every locally ℵn-bounded topological group is either precompact or ambitable. In the familiar semigroups constructed over ambitable groups, topological centres have an effective characterization.