1,467 reputation
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bio website math.wisc.edu/~josizemore
location UW-Madison
age 30
visits member for 4 years, 2 months
seen yesterday
I am a grad student postdoc at UCLA University of Wisconsin, Madison studying von Neumann Algebras, particularly classification of II_1 factors and connections with ergodic theory, descriptive set theory, and geometric and measurable group theory.

Jul
2
awarded  Curious
Apr
29
awarded  Yearling
Mar
30
answered Amenability of $l^\infty$
Dec
13
awarded  Popular Question
Sep
22
awarded  Popular Question
Sep
15
awarded  Nice Question
Sep
1
comment What is the source of this famous Grothendieck quote?
@Yemon: Yes that is what I intended (I only think of normal ones)
Aug
26
comment Versions of the spectral theorem
@Issam: Yes the spectral theorem does imply that a (non-commutative) vNA is generated by projections. Any vNA is generated by self-adjoint elements, to which you can apply the spectral theorem to get the projections. My perferred book for these topics is "An Introduction to Operator Algebras" by Kehe Zhu. It's quite expensive, though :(
Aug
24
comment Versions of the spectral theorem
With regards to 3.) In my experience the vN algebra version (ie Borel functional calculas) IS presented as the most general version. For me the way to think about it is not in terms of a the projection valued measure so much but rather in terms of the resulting isomorphism that it gives from the $C^*$ (or vN) algebra generated by $A$ and the algebra of continuous (or measureable) functions on $\sigma(A)$.
Aug
13
comment von neumann algebras and measurable spaces
@Yemon: Ah ok yes, Now I see. I will add a comment on post.
Aug
13
comment von neumann algebras and measurable spaces
@Yemon: Doesn't HB do this for you? A bounded linear function on a subspace (which these duals function are when restricted to the predual(original) basis) can be extended to a bounded linear function on the whole space, with the same bound (norm). This is how i've always thought of the non-geometric version of HB, is this not right?
Aug
13
comment von neumann algebras and measurable spaces
@Yemon: I got your comment, I don't see the issue though, except that maybe you don't want to use axiom of choice to get a basis (since it is weaker than HB no?), but for a finite dimension subspace of $X$ it should be fine.
Jul
28
comment von neumann algebras and measurable spaces
Maybe I am mistaken, by I thought that they agreed on the unit ball.
Jul
24
comment von neumann algebras and measurable spaces
@Yemon: Yes, I did gloss over this. Though to be honest, ultrapowers are a convenient language to talk about sequences of separable algebras, and every use of ultrapowers that I know of fits into this role.
Jul
24
answered von neumann algebras and measurable spaces
Jul
23
comment What's a noncommutative set?
With regards to your last questions it is equivalent to the free group factor isomorphism problem. Specifically $L(\mathbb{F}_n)\sim L(\mathbb{F}_\infty)\Leftrightarrow L(\mathbb{F}_n)\simeq L(\mathbb{F}_\infty)$. This is because in the non-isomorphic case you need $P\otimes N\simeq P$ and these factors are prime. More generally we have that if $M, N$ are prime $II_1$ factors then $M\sim N\Leftrightarrow M\simeq N$.
Jul
13
comment Is the fundamental group of a maximal subfactor always $\mathbb{R}_{+}^{*}$?
Stable means the that $P\subset Q\simeq P\otimes\mathcal{R}\subset Q\otimes \mathcal{R}$.
Jul
12
comment What's the natural equivalence of subfactors in general?
$P^t\subset Q^t=pM_n(P)p\subset pM_n(Q)p$ for an appropriate projection $p\in P$. Similarly for $P^t\otimes\mathcal{R}\subset Q^t\otimes\mathcal{R}$, but $p\in P\otimes\mathcal{R}$ in the last case. The isomorphism type only depends on the trace of $p$ and since $P\otimes\mathcal{R}$ is a factor we get a projection with correct trace in $\mathcal{R}$. So we can assume $p\in 1\otimes\mathcal{R}$. Then we just view $M_n(P)\otimes\mathcal{R}$ as $M_n(\mathbb{C})\otimes P \otimes\mathcal{R}= P\otimes M_n(\mathcal{R})$. Since $p\in P'$ we get the amplification is happening on $\mathcal{R}$.
Jul
12
comment What's the natural equivalence of subfactors in general?
However, this notion kills any information from the fundamental group. Specifically, consider the BNP examples $P\subset Q$. Then $P$ and $Q$ are the hyperfinite $II_1$, which we call $\mathcal{R}$, which is absorbing for itself. Then we have $P^t\otimes\mathcal{R} \subset Q^t\otimes\mathcal{R}\simeq P\otimes\mathcal{R}^t\subset Q\otimes\mathcal{R}^t\simeq P\otimes\mathcal{R}\subset Q\otimes \mathcal{R}$. This will always happen if the absorbing factor ($M$ above) has full fundamental group, and anything that absorbs $\mathcal{R}$ is a McDuff factor and has full fundamental group.
Jul
11
comment What's the natural equivalence of subfactors in general?
About existence, yes given any finite collection of $II_1$ factors $P_1, ..., P_k$. Consider the the infinite tensor product factor $\bigotimes (P_1\otimes\cdots\otimes P_k)$. This will be absorbing for all the $P_i$.