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Takesaki duality for weak* closed $L^p$-operator crossed products

Functional Analysis 2026-04-21 v1 Operator Algebras

Abstract

The aim of this paper is to study Takesaki duality for weak* closed LpL^p-operator crossed product Wp(G,A,α)W^*_p(G,A,\alpha), where GG is a countable discrete Abelian group, AA is a unital separable weak* closed LpL^p-operator algebra (p>1p>1), and α\alpha is a weak* continuous pp-completely isometric action of GG on AA. In this paper, we construct a weak* continuous homomorphism Φ\Phi from Wp(G^,Wp(G,A,α),α^)W^*_p(\hat{G},W^*_p(G,A,\alpha),\hat{\alpha}) to B(lp(G))ˉA\mathcal{B}(l^{p}(G))\bar{\otimes}A. We show that Φ\Phi is an isomorphism if and only if either p=2p=2 or GG is finite, and Φ\Phi is an isometric isomorphism if either p=2p=2 or GG is trivial. It is also proved that Φ\Phi is equivariant for the double dual action α^^\hat{\hat{\alpha}} of GG on Wp(G^,Wp(G,A,α),α^)W^*_p(\hat{G},W^*_p(G,A,\alpha),\hat{\alpha}) and the action Adρpα\mathrm{Ad}\rho_p\otimes\alpha of GG on B(lp(G))ˉA\mathcal{B}(l^p(G))\bar{\otimes} A. Furthermore, we prove that Wp(G^,Wp(G,A,α),α^)W^*_p(\hat{G},W^*_p(G,A,\alpha),\hat{\alpha}) is weak* continuous isometrically isomorphic to B(lp(G))ˉA\mathcal{B}(l^{p}(G))\bar{\otimes}A if and only if either p=2p=2 or GG is trivial, and Wp(G^,Wp(G,A,α),α^)W^*_p(\hat{G},W^*_p(G,A,\alpha),\hat{\alpha}) is weak* continuous isomorphic to B(lp(G))ˉA\mathcal{B}(l^{p}(G))\bar{\otimes}A if and only if either p=2p=2 or GG is finite when A=MnpA=M_n^p. This shows that Takesaki duality theorem of von Neumann algebras can be generalized to weak* closed L2L^2-operator algebras, and this theorem can not be generalized to weak* closed LpL^p-operator algebras when p(1,){2}p\in (1,\infty)\setminus\{2\}.

Keywords

Cite

@article{arxiv.2604.16946,
  title  = {Takesaki duality for weak* closed $L^p$-operator crossed products},
  author = {Zhen Wang},
  journal= {arXiv preprint arXiv:2604.16946},
  year   = {2026}
}