On factorisation schemes for the electron parton distribution functions in QED

Abstract

The electron, positron, and photon Parton Distribution Functions (PDFs) of the unpolarised electron have recently been computed at the next-to-leading logarithmic accuracy in QED, by adopting the $\overline{\rm MS}$ factorisation scheme. We present here analogous results, obtained by working in a different framework that is inspired by the so-called DIS scheme. We derive analytical solutions relevant to the large-$z$ region, where we show that the behaviour of the PDFs depends in a dramatic way on whether running-$\alpha$ effects are included to all orders, as opposed to being truncated to some fixed order. By means of suitable initial and evolution conditions, next-to-leading logarithmic accurate PDFs are obtained whose large-$z$ functional forms are identical to those of their leading logarithmic counterparts.