Twisted Connes–Popa rigidity conjecture for ICC property (T) groups

From papers

Let GG be an ICC property (T) group, let HH be an arbitrary countable ICC group, and let d:G×GTd:G\times G\to\mathbb{T} and c:H×HTc:H\times H\to\mathbb{T} be 22-cocycles. For t>0t>0, suppose that

Ψ:Ld(G)tLc(H)\Psi:\mathcal{L}_d(G)^t\to\mathcal{L}_c(H)

is a *-isomorphism. Twisted Connes–Popa rigidity conjecture. Then t=1t=1, there is a group isomorphism δ:GH\delta:G\to H such that dd is cohomologous to cδc\circ\delta, and there exist a map ξ:GT\xi:G\to\mathbb{T}, a multiplicative character η:GT\eta:G\to\mathbb{T}, and a unitary wLd(H)w\in\mathcal{L}_d(H) satisfying

d(g,h)=ξgξhc(δ(g),δ(h))ξghd(g,h)=\xi_g\xi_hc(\delta(g),\delta(h))\overline{\xi_{gh}}

and

Ψ(ug)=ηgξgwvδ(g)w,for all gG.\Psi(u_g)=\eta_g\xi_gwv_{\delta(g)}w^*,\qquad\text{for all }g\in G.

This is proposed as an extension of Popa's strengthening of Connes' rigidity conjecture to twisted group factors. The source gives preceding results supporting the formulation but does not state that it is resolved.

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Sources & referencesView supporting material

Primary source

Ionuţ Chifan, Adriana Fernández Quero, Denis Osin and Hui Tan, “W^*-superrigidity for property (T) groups with infinite center”, arXiv:2503.12742 (2026).

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