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Necessary conditions for $K_0(I_x\bigotimes A)$ to be the trivial group

Let $A$ be a unital $C^*$-Algebra with non-trivial $K_0$ group. Define $CA = \{f\in C\big([0, 1], A\big)\,\vert\,f(0) = 0\}$. It can be shown that $CA$ is homotopic equivalent to the set $\{0\}$ and ...
Sanae Kochiya's user avatar
0 votes
0 answers
91 views

Proof of the isomorphism of the Toeplitz algebra and the algebra generated by the element and the relation

Please tell me where can I see the proof of this well-known fact? enter image description here
Soar Appell's user avatar
2 votes
1 answer
525 views

Difference in tracial and finite von Neumann algebras

A tracial von Neumann algebra $(M,\tau)$ is a von Neumann algebra with a faithful normal tracial state $\tau$ on $M$. That is, $\tau$ is a function from $M \to \mathbb{C}$ such that it is a faithful ...
Anupam Ah's user avatar
  • 163
2 votes
0 answers
202 views

The trigonometric $C^*$-algebra

The trigonometric $C^*$-algebra is the universal $C^*$-algebra generated by $\mathcal{G}=\{x,y,z\}$ subject to relations \begin{align}x^2=x=x^*, &\quad y^2=y=y^*\\ [x, z]=y, &\quad [y,z]=...
Ali Taghavi's user avatar
2 votes
0 answers
70 views

The $K_0$ mapping of an automorphism induced by a derivation

Let $\mathfrak{A}$ be a unital $C^*$-Algebra and let $\delta: \mathfrak{A} \rightarrow \mathfrak{A}$ be a linear map that is not constantly zero and satisfies, for every $A, B\in\mathfrak{A}$, $\delta(...
Sanae Kochiya's user avatar
5 votes
1 answer
212 views

States "absorbed" by a Haar idempotent on a compact quantum group

Firstly, a small question of nomenclature. If $(S,\bullet)$ is a magma, is there good terminology to relate $a$ to $b$ when $$a\bullet b=b=b\bullet a?$$ Can we say that $b$ absorbs $a$? Can we say ...
JP McCarthy's user avatar
  • 1,027
10 votes
1 answer
283 views

Faithful extreme traces on group C*-algebras

Let $G$ be a discrete amenable, residually finite, ICC(i.e. each non-trivial conjugacy class is infinite) group. Let $C^*_r(G)$ be the reduced group $C^*$-algebra of $G$. Since $G$ is ICC the (...
Caleb Eckhardt's user avatar
1 vote
0 answers
137 views

Representation of states in $C^*$-algebras

Let $\mathfrak{A}$ be a $C^* $-algebra, let $\pi : \mathfrak{A} \to \mathcal{B}(H)$ be a representation of $\mathfrak{A}$ on the space of bounded linear operators on a Hilbert space $H$ and let $\...
MBolin's user avatar
  • 139
6 votes
2 answers
477 views

Linear map between projective finitely generated Hilbert modules is adjointable

Let $A$ be a (unital) $C^*$-algebra and $X,Y$ right Hilbert $A$-modules which are finitely generated and projective. It seems to be well-known that if $T: X \to Y$ is an $A$-linear map, then $T$ is ...
Andromeda's user avatar
  • 175
10 votes
1 answer
518 views

For what kind of $C^*$ algebras does the inequality $\frac{(ab+ba)}{2}\leq\frac{ a^p}{p} +\frac{b^q }{q}$ hold for $a,b>0$?

Assume that $\frac{1}{p}+\frac{1}{q}=1$ for two positive real numbers $p,q$. For what kind of $C^*$ algebras $A$ does the following hold: $$\frac{ab+ba}{2}\leq \frac{a^p}{p}+\frac{b^q}{q}$$ $\...
Ali Taghavi's user avatar
0 votes
1 answer
190 views

Are the ideals in two $C^*$-algebras the same?

Let $V_{1}, V_{2}$ be the commuting isometries. By Wold decomposition theorem, we know that $V_{i}$ admits decomposition $$V_i \cong V^s_{i}\oplus V^{u}_{i},$$ where $V^{s}_{i}$ is the shift and $V^{u}...
Andy's user avatar
  • 139
4 votes
1 answer
332 views

Support projection vs closed support projection of a normal state in enveloping von Neumann algebra

I preface this by saying that I am fairly new to the enveloping von Neumann algebra scene, so there may be some gaps in my understanding. Given a $C^*$-algebra $A$ and a state $\phi$ on $A$, one may ...
Sean's user avatar
  • 135
1 vote
0 answers
87 views

irreducible subfactor inclusion and commutativity of induced projections

Let $N\subset M$ be an irreducible subfactor inclusion, i.e., $N'\cap M =\mathbb C1$, acting on a Hilbert space $H$. Let $\Omega\in H$. Does it follow that the projections onto $[N\Omega]$ and $[M'\...
Lau's user avatar
  • 759
1 vote
1 answer
129 views

Which elements live in the image of the canonical map $X \otimes_\mathcal{F} M \to B(M_*, X)$?

Let $X\subseteq B(H)$ be an operator system and let $M\subseteq B(K)$ be a von Neumann algebra. We form the Fubini-tensor product $$X \otimes_\mathcal{F} M := \{z \in B(H\otimes K): (\sigma\otimes \...
J. De Ro's user avatar
  • 525
5 votes
1 answer
428 views

Separable C* algebras and type I states

Let $A$ be a separable $C^*$-algebra and let $\omega$ be a state on $A$. Then there is an "orthogonal" probability measure $\mu$ on the pure state space $P(A)$ of $A$ such that $\omega(x) = \...
Lau's user avatar
  • 759
8 votes
1 answer
286 views

Commutator ideal in nonunital C*-algebra

Let $A$ be a C*-algebra that has no one-dimensional irreducible representations, that is, there is no (closed) two-sided ideal $I\subseteq A$ such that $A/I\cong\mathbb{C}$. Let $J$ denote the (not ...
Hannes Thiel's user avatar
  • 3,497
4 votes
1 answer
133 views

A $C^*$ algebraic analogy of the concept of complemented subspace in the particular case of $\ell^\infty$

Let $A$ be a $C^*$ algebra. A $C^*$ subalgebra $C\subset A$ is said to be $C^*$ algebraic complemented of $A$ if there exist a $C^*$ subalgebra $D\subset A$ with $A=C\oplus D$ and the obvios mapping $...
Ali Taghavi's user avatar
1 vote
1 answer
177 views

Commuting and generating subfactors of $ B(H)$

I have a question on subfactors of $B(H)$ (the von Neumann algebra of bounded operators on a complex Hilbert space). Say I have a subfactor $M$ of $B(H)$. Is it true that another subfactor $N \subset ...
Lau's user avatar
  • 759
1 vote
0 answers
106 views

A locally convex $C^*$ algebraic structure on the disk algebra

A locally convex $C^*$ algebra is a locally convex topological vector space $A$ whose topology is generated by a familly of complete $C^*$ semi norm and $A$ is a $*$ algebra. Moreover all algebra ...
Ali Taghavi's user avatar
2 votes
1 answer
205 views

External tensor product of Hilbert modules

I am reading Lance's book "Hilbert $C^*$-modules". In particular, I want to understand how to construct the (external) tensor product of Hilbert $C^*$-modules. Consider the following ...
Andromeda's user avatar
  • 175
1 vote
0 answers
178 views

A locally convex $C^*$ algebra without zero divisor

Let we have a locally convex $C^*$ algebra $A$. That is $A$ is a TVS equipped with an algebra and an involution structure such that all operations are continuous. Moreover the topology on $A$ ...
Ali Taghavi's user avatar
3 votes
0 answers
219 views

Can any POVM be induced by a quantum instrument?

I suspect this is the obvious result of something in operator algebras, but that's far outside my field. Recall that a projection-valued measure is a map $E$ from a sigma-algebra $\mathcal{F}$ on ...
Yonah Borns-Weil's user avatar
4 votes
2 answers
157 views

Is a unital $*$-morphism from a unital $C^*$-algebra $A$ to $\operatorname{End}_{\mathbb{C}}(K)$ automatically contractive?

Let $A$ be a unital $C^*$-algebra and let $K$ be an inner product space (not necessarily complete!). Let $\pi: A \to \operatorname{End}_{\mathbb{C}}(K)$ be a unital algebra homomorphism such that $$\...
Andromeda's user avatar
  • 175
3 votes
1 answer
121 views

Impact of annihilators in C*-algebras

Let $A$ be a unital C*-algebra. Let $S\subseteq A$. We put $$\operatorname{Ann}_r(S)=\{a\in A : \forall s\in S,~ ~as=0\}$$ Suppose that $A$ satisfies the following property: For every $S\subseteq ...
ABB's user avatar
  • 4,058
5 votes
1 answer
219 views

An inequality in C*-algebras

Let $A$ be a non-unital C*-algebra, and let $\pi: A\to B(A)$ defined by $\pi(a)(x)=ax$ be the left representation of A. Is the following inequality correct? $$\lVert I+ \pi(a) \rVert\ge 1$$ for all $a ...
Diako paez's user avatar
3 votes
1 answer
743 views

Completions of $C(X)$ with respect to the topologies generated by states

I have no intuition in this field so excuse me if this is trivial. Let $X$ be a compact Hausdorff space, and $C(X)$ the algebra of continuous functions on $X$ with the usual $\sup$-norm. This is a $C^*...
Sergei Akbarov's user avatar
7 votes
0 answers
135 views

Is every quasi-nilpotent element in a C$^*$-algebra a norm-limit of nilpotent elements?

Let $A$ be a C$^*$-algebra. I have seen theorems either stating or implying that if $A$ is the algebra of bounded linear operators on a separable Hilbert space (Herrero et al.), or the Calkin algebra, ...
Douglas Somerset's user avatar
3 votes
1 answer
424 views

A trace inequality between self-adjoint operators

Let $A$ and $B$ be self-adjoint operators on some Hilbert space and $B$ is postive. Suppose we have $-B\leq A\leq B$.Is it true then that $\|A\|_p\leq\|B\|_p$ where $\|.\|_p$ is the Schatten-$p$ norm ...
A beginner mathmatician's user avatar
9 votes
2 answers
243 views

Lifting quasi-nilpotent elements in C$^*$-algebras

Let $A$ be a C$^*$-algebra with closed two-sided ideal $I$. Set $B=A/I$ and let $\pi:A\to B$ be the quotient map. Suppose that $b\in B$ is quasi-nilpotent. Does there exist quasi-nilpotent $a\in A$ ...
Douglas Somerset's user avatar
4 votes
2 answers
298 views

Takesaki volume II chapter VII lemma 1.15

Consider the following fragments from Takesaki's second volume "Theory of operator algebras" in chapter VII on weight theory, lemma 1.15. Here $\mathcal{M}$ is a von Neumann algebra and $\...
Andromeda's user avatar
  • 175
1 vote
0 answers
45 views

Examples of TRO $V $ and $C^{\ast} $-algebra $B $ for which $V\otimes^hB $ is a TRO

Let $V $ be a ternary ring of operator(TRO) and $B $ be a $\mathbb {C}^{\ast} $-algebra. Let $V \otimes^hB $ denotes the Haagerup tensor product of $V $ and $B $. Obviously if $V $ or $B $ is $\mathbb ...
Math Lover's user avatar
  • 1,115
2 votes
0 answers
228 views

Irreducible group representation(algebraic and topological irreducibility)

In page 280 of "C^* algebra" by Dixmier, in the context of group representation, it is written 'We never encounter the concept of algebraic irreducibility except in finite dimensional ...
Ali Taghavi's user avatar
5 votes
0 answers
137 views

Trying to prove a seemingly easy fact on ideals of ternary C*-algebras

Currently I'm reading the paper by Abadie and Ferraro titled Applications of ternary rings to $C^*$-algebras. Recall that a $C^{\ast}$-ternary ring is a complex Banach space $M$, equipped with a ...
Math Lover's user avatar
  • 1,115
1 vote
1 answer
172 views

What is a C*-algebra generated by a subset of a direct sum of C*-algebras equal to?

I'm studying C-algebras and I don't know how to address the following question: let $(A_k)_{k\in \mathbb{N}}$ a family of C-algebras and let $\mathcal{G}$ a subset of $\displaystyle\bigoplus_{k\in \...
Xavier González's user avatar
1 vote
0 answers
113 views

Is it true that $\omega = \sum_{(k,l)\in I^2}\omega(p_k - p_l)$

Let $\{p_i\}_{i \in I}$ be a collection of projections in a $C^*$-algebra $A$ such that $\sum_{i \in I} p_i = 1$ in the strict topology (note here that $1$ is the unit of the multiplier algebra $M(A)$)...
Andromeda's user avatar
  • 175
9 votes
1 answer
460 views

Is a $*$-automorphism $M(A) \to M(A)$ automatically strictly continuous?

Let $A$ be a (non-unital) $C^*$-algebra with multiplier $C^*$-algebra $M(A)$. Let $\phi: M(A) \to M(A)$ be a $*$-automorphism. Is it true that $\phi$ is automatically strictly continuous (on bounded ...
J. De Ro's user avatar
  • 525
-1 votes
1 answer
230 views

Determine whether the center of a $C^*$-algebra is 0

Let $G$ be a locally compact group and $A$ be a non-unital $C^*$-algebra. )$(A,G,\alpha)$ is a $C^*$-dynamical sysytem. The space of all continous functions from $G$ to $A$ with compact support is ...
math112358's user avatar
1 vote
0 answers
129 views

Socle of an operator algebra

Let $H, K$ be Hilbert spaces. Let $A\subseteq B(H)$ be a nonselfadjoint closed subalgebra such that the identity map is in $A$. Let $C_A$ denote the $C^*$-algebra generated by $A$. Q1: (this question ...
Onur Oktay's user avatar
  • 2,605
2 votes
1 answer
374 views

A C*-algebra enjoying some different C*-norms

Does there exist any C*-algebra $(A,\|\cdot\|)$ enjoying the following property? $\bullet$ There exists a norm $|\cdot|$ on $A$ with $\|\cdot\|\leq|\cdot|$ such that $(A,|\cdot|)$ is a pre C*-...
ABB's user avatar
  • 4,058
9 votes
3 answers
568 views

Defining the abstract tensor product of W*-algebras via a universal property

I am playing around a bit with $W^*$-algebras, and I'm trying to come up with a definition for the $W^*$-algebraic tensor product. Here is my first attempt: It is easy to show that such an object ...
Andromeda's user avatar
  • 175
0 votes
0 answers
88 views

$*$–homomorphisms of the center of $C^*$-algebras

Let $A$ and $B$ be $C^*$-algebras with centers $Z_A$ and $Z_B$. Suppose $\rho:A\rightarrow B$ is a surjective $*$- homomorphism. It is easy to check $\rho(Z_A)\subset Z(B)$. I wonder how to assure ...
math112358's user avatar
2 votes
2 answers
158 views

Decomposition of an element as a difference of positive elements in the definition subalgebra of a weight (Takesaki)

I originally asked this on MSE, but did not get an answer there. Let $M$ be a von Neumann algebra. Let $\varphi: M_+ \to [0, \infty]$ be a weight on $M$. Consider \begin{align*}&\mathfrak{p}_\...
Andromeda's user avatar
  • 175
1 vote
1 answer
136 views

The closure of selfadjoint elements of an algebra whose spectrum consist of rational numbers

Let $H$ be a seperable complex Hilbert space. What is the closure of the set of all self adjoint operators in $B(H)$ whose spectrum is a subset of the rational number $\mathbb{Q}$. Apart from finite ...
Ali Taghavi's user avatar
1 vote
0 answers
57 views

Is the universal representation an order isomorphism?

Let $A$ be a Banach *-algebra. By a *-representations of $A$, we mean a *-homomorphism $\pi:A\to B(H_\pi)$, where $B(H_\pi)$ is the space of all bounded linear maps on a Hilbert space $H_\pi$. Let $\...
ABB's user avatar
  • 4,058
3 votes
1 answer
290 views

Approximation of continuous projections on a manifold by smooth idempotents

Every continuous vector bundle on a closed smooth manifold $M$ has a smooth structure. On the other hand, every vector bundle $E$ is the image of a trivial bundle $M\times\mathbb{C}^n$ under some ...
geometricK's user avatar
  • 1,903
1 vote
1 answer
118 views

Let $V$ be a TRO such that $A(V)= \mathbb{C}$, what can we say about $V$?

Let $V$ be a TRO i.e. closed subspace of $B(H,K)$ such that $xy^*z \in V$ for all $x,y,z \in V$. Let $C(V)$ and $D(V)$ denotes the $C^{\ast}$-algebra generated by $VV^{\ast}$ and $V^*V$ respectively. ...
Math Lover's user avatar
  • 1,115
2 votes
1 answer
218 views

Extending a $\sigma$-weakly continuous map: Takesaki IV.5.13

Consider the following fragment from chapter IV in Takesaki's book "Theory of operator algebra I": Why is the boxed line true? Takesaki argues that $$\theta_0: \mathscr{M}_1\otimes_{\...
Andromeda's user avatar
  • 175
2 votes
1 answer
297 views

Predual theorem proof in Takesaki's volume I

Consider the following fragment from Takesaki's book "Theory of operator algebra I" (Section III.3 ,p133-134). Why is the boxed line true? I can see that $\epsilon: \widetilde{A}\to A$ is ...
Andromeda's user avatar
  • 175
3 votes
0 answers
160 views

Construct a non-unital nuclear $C^*$-algebra without tracial states such that its multiplier algebra is also traceless

Let $H$ be an infinite dimensional separable Hilbert space. The set $K(H)$ of all compact operators is a non-unital nuclear $C^*$-algebra which has no tracial states and the multiplier algebra of $K(...
math112358's user avatar
3 votes
1 answer
255 views

Takesaki: Lemma about enveloping von Neumann algebra

Consider the following lemma with proof from Takesaki's book "Theory of operator algebra I" (p121): It appears to me that Takesaki claims at the end of the proof that $\pi(A)_1$ is $\sigma$-...
Andromeda's user avatar
  • 175

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