1 Pion Form Factor and Quark Mass Evolution in a Light-Front Quark Model

We discuss the soft contribution to the elastic pion form factor with the mass evolution from current to constituent quark being taken into account in a light-front quark model(LFQM). The pion electromagnetic (EM) form factor is of great interest for the study of Quantum Chromodynamics (QCD). At low momentum transfers (Q 2) nonperturbative QCD (NPQCD) dominates, while at large Q 2 perturbative QCD (PQCD) can be used to calculate the asymptotic form factor; and the transition from NPQCD to PQCD has long been of interest. Since PQCD can only be used for Q 2> 1 GeV 2, light-front (LF) quantization methods [1] may be most useful for exploring NPQCD. In fact, many previous quark models [2–5] have used the constituent quark mass in the analysis of the hadron properties especially at low momentum transfer region. This constituent quark model has been quite succesful in describing static properties of a hadron such as the form factor, charge radius, and decay constant etc. On the other hand, the approach based on the quantum field theory such as the Dyson Schwinger Equations(DSEs) [6] uses the running mass instead of constituent mass and it also gives properties of the pion that are in agreement with the experimental data. Thus, in this talk, we present the quark mass evolution effect on the pion in a light-front quark model(LFQM) [7]. In the present work we restrict ourselves to the soft NPQCD part with a LFQM,