The noncommutative Brouwer retract conjecture for C*-algebras

Let AA be a unital CC^*-algebra with a free action of Z/2Z\mathbb{Z}/2\mathbb{Z}, and let ΓA\Gamma A be its cone C*-algebra. Let ev1/2:ΓAA\operatorname{ev}_{1/2}:\Gamma A\to A be evaluation at the midpoint.

Noncommutative Brouwer retract conjecture. There is no *-homomorphism

γ:AΓA\gamma:A\longrightarrow\Gamma A

such that

ev1/2γ=idA.\operatorname{ev}_{1/2}\circ\gamma=\operatorname{id}_A.

This is proposed as a noncommutative analogue of the retract formulation of Brouwer's fixed-point theorem and is an immediate consequence of the preceding cone Borsuk–Ulam conjecture. The source says it holds for the even-dimensional quantum θ\theta-ball families, but does not establish it in general.

Sources & referencesView supporting material

Primary source

Ludwik Dabrowski, “Towards a noncommutative Brouwer fixed-point theorem”, arXiv:1504.03588 (2015).

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