Bounds on the spacelike pion electromagnetic form factor from analyticity and unitarity

Abstract

We use the recently measured accurate BaBaR data on the modulus of the pion electromagnetic form factor, $F_{\pi }(t)$, up to an energy of 3 GeV, the I=1 $P$-wave phase of the $\pi \pi$ scattering amplitude up to the $\omega -\pi$ threshold, the pion charge radius known from Chiral Perturbation Theory, and the recently measured JLAB value of $F_{\pi }$ in the spacelike region at $t=-2.45{\mathrm{GeV}}^2$ as inputs in a formalism that leads to bounds on $F_{\pi }$ in the intermediate spacelike region. We compare our constraints with experimental data and with perturbative QCD along with the results of several theoretical models for the non-perturbative contributions proposed in the literature.

Comments: 6 pages, using PoS style files, 2 figures; talk given at QNP 2012, Palaiseau, France, April 16-20, 2012