English

Induction, absorption and weak containment of *-representations of Banach *-algebraic bundles

Operator Algebras 2022-11-16 v2

Abstract

Given a Fell bundle B={Bt}tG\mathcal{B}=\{B_t\}_{t\in G} over a LCH group and a closed subgroup HG,H\subset G, we show that all the *-representations of BH:={Bt}tH\mathcal{B}_H:=\{B_t\}_{t\in H} can be induced to *-representations of B\mathcal{B} by means of Fell's induction process; which we describe as induction via a *-homomorphism qHB ⁣:C(B)B(XC(BH)).q^{\mathcal{B}}_H\colon C^*(\mathcal{B})\to \mathbb{B}(X_{C^*(\mathcal{B}_H)}). The quotients CH(B):=qHB(C(B))C^*_H(\mathcal{B}):=q^{\mathcal{B}}_H(C^*(\mathcal{B})) are intermediate to C(B)=CG(B)C^*(\mathcal{B})= C^*_G(\mathcal{B}) and Cr(B)=C{e}(B)C^*_{r}(\mathcal{B})=C^*_{\{e\}}(\mathcal{B}) because every inclusion of subgroups HKGH\subset K\subset G gives a unique quotient map qHKB ⁣:CK(B)CH(B)q^{\mathcal{B}}_{HK}\colon C^*_K(\mathcal{B})\to C^*_H(\mathcal{B}) such that qHKBqKB=qHB.q^{\mathcal{B}}_{HK}\circ q^{\mathcal{B}}_K=q^{\mathcal{B}}_H. All along the article we try to find conditions on B,\mathcal{B}, G, HG,\ H and KK (e.g. saturation, nuclearity or weak containment) that imply qHKBq^{\mathcal{B}}_{HK} is faithful. One of our main tools is a blend of Fell's absorption principle (for saturated bundles) and a result of Exel and Ng for reduced cross sectional C*-algebras. We also show that given an imprimitivity system T,P\langle T,P\rangle for B\mathcal{B} over G/H,G/H, if HH is open or has open normalizer in G,G, then TT is weakly contained in a *-representation induced from BH\mathcal{B}_H (even if B\mathcal{B} is not saturated). Given normal and closed subgroups of G,G, HK,H\subset K, we construct a Fell bundle C\mathcal{C} over G/KG/K such that Cr(C)=CH(B).C^*_r(\mathcal{C})=C^*_H(\mathcal{B}). We show that qHBq^{\mathcal{B}}_H is faithful if and only if both q{e}Cq^{\mathcal{C}}_{\{e\}} and qHBKq^{\mathcal{B}_K}_H are.

Keywords

Cite

@article{arxiv.2009.01064,
  title  = {Induction, absorption and weak containment of *-representations of Banach *-algebraic bundles},
  author = {Damián Ferraro},
  journal= {arXiv preprint arXiv:2009.01064},
  year   = {2022}
}

Comments

The whole article was rewritten and the title changed. We introduce the so called Derighetti condition to correct an error in the previous version. The major conclusions remain unaffected