Renormalon Phenomena in Jets and Hard Processes

The renormalon' or dispersive’ method for estimating non-perturbative corrections to QCD observables is reviewed. The corrections are power-suppressed, i.e. of the form $A\mathrm{/}{Q}^p$ where $Q$ is the hard process momentum scale. The renormalon method exploits the connection between divergences of the QCD perturbation series and low-momentum dynamics to predict the power, $p$. The further assumption of an approximately universal low-energy effective strong coupling leads to relationships between the coefficients $A$ for different observables. Results on $1\mathrm{/}{Q}^2$ corrections to deep inelastic structure functions and $1\mathrm{/}Q$ corrections to event shapes are presented and compared with experiment. Shape variables that could be free of $1\mathrm{/}Q$ and $\text{as}(Q^2)\mathrm{/}Q$ corrections are suggested.