Burghelea's conjecture on periodic cyclic homology of group algebras

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Let GG be a discrete group, let K(G,1)K(G,1) be an Eilenberg–Mac Lane space, and let ⟨G⟩∞\langle G\rangle^{\infty} denote the conjugacy classes of elements of infinite order. For x∈⟨G⟩∞x\in\langle G\rangle^{\infty}, write GxG_x for the centralizer of xx, Nx=Gx/⟨x⟩N_x=G_x/\langle x\rangle for the reduced centralizer, and let T∗(x,Q)T_*(x,\mathbb{Q}) be the term in Burghelea's decomposition of the periodic cyclic homology of QG\mathbb{Q}G, fitting into the short exact sequence

0→lim←⁡1{H∗−1+2n(Nx,Q)}→T∗(x,Q)→lim←⁡{H∗+2n(Nx,Q)}→0.0\to\varprojlim{}^1\{H_{*-1+2n}(N_x,\mathbb{Q})\}\to T_*(x,\mathbb{Q})\to\varprojlim\{H_{*+2n}(N_x,\mathbb{Q})\}\to 0.

Burghelea's conjecture. If K(G,1)K(G,1) has the homotopy type of a finite CW-complex, then

T∗(x,Q)=0T_*(x,\mathbb{Q})=0

for all x∈⟨G⟩∞x\in\langle G\rangle^{\infty}. Burghelea's formula expresses periodic cyclic homology in terms of these groups for infinite-order conjugacy classes; the conjecture asserts their vanishing under a finiteness hypothesis on K(G,1)K(G,1), and the supplied source gives no resolution.

References

Primary source

Alexander Dranishnikov, “On Burghelea Conjecture”, arXiv:1612.08700 (2017).

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