2
$\begingroup$

We know that if $i:R_n\rightarrow C_n$ is an isometry then for any $n$-dimensional operator space E, there is a factorization $i=uv$ with $v:R_n\rightarrow E$, $u:E\rightarrow C_n$ such that $\|u\|_{cb}\|v\|_{cb}=n^{1/2}$. The question is, if E is a homogeneous Hilbertian operator space can we find $u$ and $v$ such that they are isometries?

Improve this question
$\endgroup$

1 Answer 1

Reset to default
2
$\begingroup$

Yes. See the proof of Proposition 10.1 in Pisier's book. The idea is simple: if you start from any factorization $uv$, by the polar decomposition you can assume that both maps are diagonal in an orthonormal basis. Averaging these diagonal maps over all permutations of the basis does not increase the cb norm, and yields maps that are multiple of the identity.

Improve this answer
$\endgroup$
3
  • $\begingroup$ Thank you. Which book? Introduction to Operator Space Theory? $\endgroup$
    – Sean
    Commented Jun 25, 2013 at 22:58
  • $\begingroup$ Yes, this book. $\endgroup$
    – Mikael de la Salle
    Commented Jun 25, 2013 at 23:04
  • $\begingroup$ Cheers, that makes sense, I'll think about it, now it's not very obvious but it helps for sure. $\endgroup$
    – Sean
    Commented Jun 25, 2013 at 23:05

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .