Nucleon axial form factors from two-flavour Lattice QCD

Abstract

We present preliminary results on the axial form factor $G_A(Q^2)$ and the induced pseudoscalar form factor $G_P(Q^2)$ of the nucleon. A systematic analysis of the excited-state contributions to form factors is performed on the CLS ensemble `N6' with $m_{\pi }=340\text{MeV}$ and lattice spacing $a\sim 0.05\text{fm}$. The relevant three-point functions were computed with source-sink separations ranging from $t_s\sim 0.6\text{fm}$ to $t_s\sim 1.4\text{fm}$. 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.

Comments: 7 pages, 12 figures; talk presented at Lattice 2014 -- 32nd International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia University New York, NY