Kl3 and pion form factors using partially twisted boundary conditions

Authors :: Boyle, P. A.
Flynn, J. M.
Jüttner, A.
Kelly, C.
de Lima, H. Pedroso
Maynard, C. M.
Sachrajda, C. T.
Zanotti, J. M.
Source :: PoS LATTICE2008:287,2008
Publication Year :: 2008
Abstract: We compute the Kl3 and pion form factors using partially twisted boundary conditions. The twists are chosen so that the Kl3 form factors are calculated directly at zero momentum transfer (q^2=0), removing the need for a q^2 interpolation, while the pion form factor is determined at values of q^2 close to q^2=0. The simulations are performed on an ensemble of the RBC/UKQCD collaboration's gauge configurations with Domain Wall Fermions and the Iwaski gauge action with an inverse lattice spacing of 1.73(3) GeV. Simulating at a single pion mass of 330 MeV, we find the pion charge radius to be < r^2>_{330 MeV}=0.354(31) fm^2 which, using NLO SU(2) chiral perturbation theory, translates to a value of <r_\pi^2>=0.418(31) fm^2 for a physical pion. For the value of the Kl3 form factor, f_{K\pi}^+(q^2), determined directly at q^2=0, we find a value of f_{K\pi}^+(0)=0.9742(41) at this particular quark mass, which agrees well with our earlier result (0.9774(35)) obtained using the standard, indirect method.<br />Comment: 7pages, 3 figures, presented at the XXVI International Symposium on Lattice Field Theory, July 14-19, 2008, Williamsburg, Virginia, USA