ASYMPTOTIC LIMITS AND THE STRUCTURE OF THE PION FORM-FACTOR

We use dispersive techniques to address the behavior of the pion form factor as Q(2)-->infinity and Q(2)-->0. We perform the matching with t he constraints of perturbative QCD and chiral perturbation theory in t he high-energy and low-energy limits, leading to four sum rules. We pr esent a version of the dispersive input which is consistent with the d ata and with all theoretical constraints. The results indicate that th e asymptotic perturbative QCD limit is approached relatively, slowly, and give a model-independent determination of low-energy chiral parame ters. [S0556-2821(97)02123-1].