Published online by Cambridge University Press: 24 June 2021
For any (Hausdorff) compact group G, denote by $\mathrm{cp}(G)$ the probability that a randomly chosen pair of elements of G commute. We prove that there exists a finite group H such that
$\mathrm{cp}(G)= {\mathrm{cp}(H)}/{|G:F|^2}$, where F is the FC-centre of G and H is isoclinic to F with
$\mathrm{cp}(F)=\mathrm{cp}(H)$ whenever
$\mathrm{cp}(G)>0$. In addition, we prove that a compact group G with
$\mathrm{cp}(G)>\tfrac {3}{40}$ is either solvable or isomorphic to
$A_5 \times Z(G)$, where
$A_5$ denotes the alternating group of degree five and the centre
$Z(G)$ of G contains the identity component of G.
The research of the second author was in part supported by a grant from the Institute for Research in Fundamental Sciences (IPM) (No. 1400200043). This research was supported in part by a grant from School of Mathematics, Institute for Research in Fundamental Sciences.