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Nucleon form factors with 2+1 flavor dynamical domain-wall fermions

We report our numerical lattice QCD calculations of the isovector nucleon form factors for the vector and axialvector currents: the vector, induced tensor, axialvector, and induced pseudoscalar form factors. The calculation is carried out with the gauge configurations generated with N_f=2+1 dynamical domain wall fermions and Iwasaki gauge actions at beta = 2.13, corresponding to a cutoff 1/a = 1.73 GeV, and a spatial volume of (2.7 fm)^3. The up and down quark masses are varied so the pion mass lies between 0.33 and 0.67 GeV while the strange quark mass is about 12% heavier than the physical one. We calculate the form factors in the range of momentum transfers, 0.2 < q^2 < 0.75 GeV^2. The vector and induced tensor form factors are well described by the conventional dipole forms and result in significant underestimation of the Dirac and Pauli mean-squared radii and the anomalous magnetic moment compared to the respective experimental values. We show that the axialvector form factor is significantly affected by the finite spatial volume of the lattice. In particular in the axial charge, g_A/g_V, the finite volume effect scales with a single dimensionless quantity, m_pi L, the product of the calculated pion mass and the spatial lattice extent. Our results indicate that for this quantity, m_pi L > 6 is required to ensure that finite volume effects are below 1%.