A Morita theorem for dual operator algebras

Abstract

We prove that two dual operator algebras are weak$^*$ Morita equivalent if and only if they have equivalent categories of dual operator modules via completely contractive functors which are also weak$^*$-continuous on appropriate morphism spaces. Moreover, in a fashion similar to the operator algebra case, we characterize such functors as the module normal Haagerup tensor product with an appropriate weak$^*$ Morita equivalence bimodule. We also develop the theory of the $W^*$-dilation, which connects the non-selfadjoint dual operator algebra with the $W^*$-algebraic framework. In the case of weak$^*$ Morita equivalence, this $W^*$-dilation is a $W^*$-module over a von Neumann algebra generated by the non-selfadjoint dual operator algebra. The theory of the $W^*$-dilation is a key part of the proof of our main theorem.