Notes on Real Interpolation of Operator Lp-Spaces

Marius Junge, Quanhua Xu

Research output: Contribution to journalArticlepeer-review


Let ℳ be a semifinite von Neumann algebra. We equip the associated non-commutative Lp-spaces with their natural operator space structure introduced by Pisier via complex interpolation. On the other hand, for 1 < p < ∞ let Lp,p(ℳ)=(L∞(ℳ),L1(ℳ))1p,p be equipped with the operator space structure via real interpolation as defined by the second named author (J. Funct. Anal. 139 (1996), 500-539). We show that Lp,p(ℳ) = Lp(ℳ) completely isomorphically if and only if ℳ is finite dimensional. This solves in the negative the three problems left open in the quoted work of the second author. We also show that for 1 < p < ∞ and 1 ≤ q ≤ ∞ with p ≠ q(L∞(ℳ;ℓq),L1(ℳ;ℓq))1p,p=Lp(ℳ;ℓq) with equivalent norms, i.e., at the Banach space level if and only if ℳ is isomorphic, as a Banach space, to a commutative von Neumann algebra. Our third result concerns the following inequality: ‖(∑ixiq)1q‖Lp(ℳ)≤‖(∑ixir)1r‖Lp(ℳ) for any finite sequence (xi)⊂Lp+(ℳ), where 0 < r < q < ∞ and 0 < p ≤ ∞. If ℳ is not isomorphic, as a Banach space, to a commutative von Meumann algebra, then this inequality holds if and only if p ≥ r.

Original languageEnglish (US)
Pages (from-to)2173-2182
Number of pages10
JournalActa Mathematica Scientia
Issue number6
StatePublished - Nov 2021


  • 46E30
  • 47C15
  • L-spaces
  • column Hilbertian spaces
  • operator spaces
  • real interpolation

ASJC Scopus subject areas

  • General Mathematics
  • General Physics and Astronomy


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