Quantum groups with projection on von Neumann algebra level

We introduce an axiomatization of the notion of a semidirect product of locally compact quantum groups and study their properties. Our approach is slightly different from the one introduced in the thesis of S. Roy [16] and, unlike the investigations of Roy, we work within the von Neumann algebraic picture. This allows the use of powerful techniques related to crossed products by actions of locally compact quantum groups. In particular we show existence of a “braided comultiplication” on the algebra spanned by slices of “braided multiplicative unitary”.