Convolution of trace class operators over locally compact quantum groups

Zhiguo Hu, Matthias Neufang, Zhong Jin Ruan

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We study locally compact quantum groups G through the convolution algebras L1 (G) and (T(L2(G)), ⋊). We prove that the reduced quantum group C*-algebra C0 (G) can be recovered from the convolution ⋊ by showing that the right T(L2(G))-module (K(L2(G)) ⋊ T(L2(G))) is equal to C0(G). On the other hand, we show that the left T(L 2(G))-module (T(L 2(G)) ⋊ K(L2(G))) is isomorphic to the reduced crossed product C0 (Ĝ)r × C0 (G), and hence is a much larger C*-subalgebra of B(L2 (G)). We establish a natural isomorphism between the completely bounded right multiplier algebras of L1(G) and (T(L2(G)),⋊), and settle two invariance problems associated with the representation theorem of Junge-Neufang-Ruan (2009). We characterize regularity and discreteness of the quantum group G in terms of continuity properties of the convolution ⋊ on T(L 2(G)). We prove that if G is semi-regular, then the space (T(L2(G)) ⋊ B(L2(G))) of right G-continuous operators on L2(G), which was introduced by Bekka (1990) for L(G), is a unital C *-subalgebra of B(L2(G)). In the representation framework formulated by Neufang-Ruan-Spronk (2008) and Junge-Neufang-Ruan, we show that the dual properties of compactness and discreteness can be characterized simultaneously via automatic normality of quantum group bimodule maps on B(L2(G)). We also characterize some commutation relations of completely bounded multipliers of (T(L 2(G)), [⋊) over B(L2 (G)).

Original languageEnglish (US)
Pages (from-to)1043-1072
Number of pages30
JournalCanadian Journal of Mathematics
Issue number5
StatePublished - 2013


  • Banach algebras
  • Locally compact quantum groups and associated

ASJC Scopus subject areas

  • Mathematics(all)

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