Semiclassical origin of renormalons in asymptotically free theories

In asymptotically free theories ($4\mathrm{D}$ Yang-Mills and QCD, $2\mathrm{D}$ $\mathrm{O}(N)$, $\mathrm{CP}^{N-1}$ and principal chiral models), the Borel transform of perturbation series has renormalon singularities at positions set by the one-loop beta-function coefficient, not matched by any finite-action classical solution. Identify the nonperturbative sectors (saddles, fractional instantons, bions on R^{d-1} x S^1, or OPE condensates) whose imaginary ambiguities cancel the renormalon ambiguities, and demonstrate the cancellation.

An explicit computation in at least one asymptotically free theory showing order-by-order cancellation between the renormalon ambiguity and an identified nonperturbative sector.