Type 1 noncommutative Borsuk–Ulam conjecture for compact group actions

Let GG be a nontrivial compact group acting freely on a unital CC^*-algebra AA. Define the join

AC(G)={fC([0,1],AC(G)):f(0)CC(G), f(1)AC}.A\circledast C(G)=\{f\in C([0,1],A\otimes C(G)): f(0)\in \mathbb{C}\otimes C(G),\ f(1)\in A\otimes\mathbb{C}\}.

Equip AC(G)A\circledast C(G) with the diagonal action of GG. Type 1 noncommutative Borsuk–Ulam conjecture. There is no equivariant, unital *-homomorphism

ϕ:AAC(G).\phi:A\to A\circledast C(G).

This is the compact-group subcase of the Type 1 noncommutative Borsuk–Ulam conjecture, originally formulated for coactions of compact quantum groups. It asserts that a free action cannot admit an equivariant unital map from AA to its join with the acting group.

Sources & referencesView supporting material

Primary source

Alexandru Chirvasitu, Benjamin Passer and Mariusz Tobolski, “Equivariant Dimensions of Graph C*-algebras”, arXiv:1907.10010 (2020).

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