Shifts of group-like projections and contractive idempotent functionals for locally compact quantum groups

Abstract

A one to one correspondence between shifts of group-like projections on a locally compact quantum group $\mathbb{G}$ which are preserved by the scaling group and contractive idempotent functionals on the dual $\hat{\mathbb{G}}$ is established. This is a generalization of the Illie-Spronk's correspondence between contractive idempotents in the Fourier-Stieltjes algebra of a locally compact group $G$ and cosets of open subgroups of $G$. We also establish a one to one correspondence between non-degenerate, integrable, $\mathbb{G}$-invariant ternary rings of operators $X\subset L^{\infty }(\mathbb{G})$, preserved by the scaling group and contractive idempotent functionals on $\mathbb{G}$. Using our results we characterize coideals in $L^{\infty }(\hat{\mathbb{G}})$ admitting an atom preserved by the scaling group in terms of idempotent states on $\mathbb{G}$. We also establish a one to one correspondence between integrable coideals in $L^{\infty }(\mathbb{G})$ and group-like projections in $L^{\infty }(\hat{\mathbb{G}})$ satisfying an extra mild condition. Exploiting this correspondence we give examples of group like projections which are not preserved by the scaling group.

Section 5 added, establishing a one to one correspondence between non-degenerate, integrable, $\mathbb{G}$-invariant ternary rings of operators $X\subset L^{\infty }(\mathbb{G})$, preserved by the scaling group and contractive idempotent functionals on $\mathbb{G}$. A 1-1 correspondence between integrable coideals and group-like projections were extended beyond the compact case