An Ideal Correspondence Result for Crossed Products by Quantum Groups

Given a weak Kac system with duality $(\mathcal{H},V,U)$ arising from regular ${\mathrm{C}}^{\ast }$-algebraic locally compact quantum group $(\mathcal{G},\mathrm{\Delta })$, a ${\mathrm{C}}^{\ast }$-algebra $A$, and a sufficiently well-behaved coaction $\alpha$, we construct natural lattice isomorphisms from the coaction invariant ideals of $A$ to the dual coaction invariant ideals of full and reduced crossed products associated to $(\mathcal{H},V,U)$. In particular, these lattice isomorphisms are determined by either the maximality or normality of the coaction $\alpha$. This result directly generalizes the main theorem of Gillespie, Kaliszewski, Quigg, and Williams in arXiv:2406.06780, which in turn generalized an older ideal correspondence result of Gootman and Lazar for locally compact amenable groups. Throughout, we also develop basic conventions and motivate through elementary examples how crossed product ${\mathrm{C}}^{\ast }$-algebras by quantum groups generalize the classical crossed product theory.