Global QCD fit from $Q^2=0$ to $Q^2=30000$ GeV$^2$ with Regge-compatible initial condition

Abstract

In this paper I show that it is possible to use Regge theory to constrain the initial parton distribution functions of a global DGLAP fit. In this approach, both quarks and gluons have the same high-energy behaviour which may also be used to describe soft interactions. More precisely, I show that, if we parametrise the parton distributions with a triple-pole pomeron, {\em i.e.} like $\log^2(1/x)$ at small $x$, at $Q^2=Q_0^2$ and evolve these distribution with the DGLAP equation, we can reproduce $F_2^p$, $F_2^d$, $F_2^n/F_2^p$, $F_2^{\nu N}$ and $xF_3^{\nu N}$ for $W^2\ge 12.5$ GeV$^2$. In this case, we obtain a new leading-order global QCD fit with a Regge-compatible initial condition. I shall also show that it is possible to use Regge theory to extend the parton distribution functions to small $Q^2$. This leads to a description of the structure functions over the whole $Q^2$ range based on Regge theory at low $Q^2$ and on QCD at large $Q^2$. Finally, I shall argue that, at large $Q^2$, the parton distribution functions obtained from DGLAP evolution and containing an essential singularity at $j=1$ can be approximated by a triple-pole pomeron behaviour.