arXiv subjects
Publications and source records attributed to Peter A. Linnell.
Let G be a discrete group, let $p \ge 1$, and let $L^p(G)$ denote the Banach space $\{\sum_{g\in G} a_g g \mid \sum_{g\in G} |a_g|^p < \infty\}$. The following problem will be studied: given $0 \ne α\in CG$ and $0 \ne β\in L^p(G)$, is $α* β\ne 0$? We will concentrate on the case G is a free abelian or free group.
Let G be a group, let U(G) denote the set of unbounded operators on L^2(G) which are affiliated to the group von Neumann algebra W(G) of G, and let D(G) denote the division closure of CG in U(G). Thus D(G) is the smallest subring of U(G) containing CG which is closed under taking inverses. If G is a free group then D(G) is a division ring, and in this case we shall give a criterion for an element of U(G) to be in D(G). This extends a result of Duchamp and Reutenauer, which was concerned with proving a conjecture of Connes.
For x,y in R (where R denotes the real numbers) and f in L^2(R), define (x,y)f(t) = e^{2 pi i yt}f(t+x) and if L is a subset of R^2, define S(f,L) = {(x,y)f | (x,y) in L}. It has been conjectured that if f is not 0, then S(f,L) is linearly independent over C; one motivation for this problem comes from Gabor analysis. We shall prove that S(f,L) is linearly independent if f is nonzero and L is contained in a discrete subgroup of R^2, and as a byproduct we shall obtain some results on the group von Neumann algebra generated by the operators {(x,y) | (x,y) in L}. Also we shall prove these results for the obvious generalization to R^n.