Nucleon axial form factors from two-flavour Lattice QCD

We present preliminary results on the axial form factor GA(Q2) and the induced pseudoscalar form factor GP(Q2) of the nucleon. A systematic analysis of the excited-state contributions to form factors is performed on the CLS ensemble ‘N6 ’ with mpi = 340 MeV and lattice spacing a ∼ 0.05 fm. The relevant three-point functions were computed with source-sink separations ranging from ts ∼ 0.6 fm to ts ∼ 1.4 fm. We observe that the form factors suffer from non-trivial excited-state contributions at the source-sink separations available to us. It is noted that naive plateau fits underestimate the excited-state contributions and that the method of summed operator insertions correctly accounts for these effects