Very recently,Špakula and Tikuisis provide a new characterisation of (uniform) Roe algebras via quasi-locality when the underlying metric spaces have straight finite decomposition complexity. In this paper, we improve their method to deal with the L p -version of (uniform) Roe algebras for any p ∈ [1, ∞). Due to the lack of reflexivity on L 1 -spaces, some extra work is required for the case of p = 1.Mathematics Subject Classification (2010): 20F65, 46H35, 47L10.
Introduction(Uniform) Roe algebras are C * -algebras associated to metric spaces, which reflect coarse properties of the underlying metric spaces. These algebras have been well-studied and have fruitful applications, among which the most important ones would be the (uniform) coarse Baum-Connes conjecture and the Novikov conjecture (e.g., [32,33,40,41,42,43]). Meanwhile, they also provide a link between coarse geometry of metric spaces and the theory of C * -algebras (e.g., [1,11,15,16,19,20,23,29,30,32,37,39]), and turn out to be useful in the study of topological phases of matter (e.g., [17,10]) as well as the theory of limit operators in the study of Fredholmness of band-dominated operators (e.g., [14,21,31,35]).By definition, the (uniform) Roe algebra of a proper metric space X is the norm closure of all bounded locally compact operators T with finite propagation in the sense that there exists R > 0 such that for any f, g ∈ C b (X) acting on L 2 (X) by pointwise multiplication, we have f Tg = 0 provided their supports are Rseparated (i.e., the distance between the supports of f and g is at least R). Since general elements in (uniform) Roe algebras may not have finite propagation, it is usually difficult to tell what operators exactly belong to them. On the other hand, Roe [27] defined an asymptotic version of finite propagation as follows: An operator T on L 2 (X) has finite ε-propagation for ε > 0, if there is R > 0 such that for any f, g ∈ C b (X), we have f Tg ≤ ε f · g provided their supports Key words and phrases. Quasi-local operators, L p -Roe algebras, straight finite decomposition complexity.