Neutron electric dipole moment on the lattice

Shintani, Eigo; Aoki, S.; Ishizuka, N.; Kanaya, K.; Kikukawa, Y.; Kuramashi, Y.; Okawa, M.; Ukawa, A.; Yoshié, T.

Neutron electric dipole moment on the lattice

Authors

Description

We carry out a feasibility study toward a lattice QCD calculation of the neutron electric dipole moment (NEDM) in the presence of the $θ$ term using two different approaches. In the first method, we calculate the CP-odd electromagnetic form factor $F_3$, which becomes the NEDM in the zero momentum transfer limit. At the first order in $θ$, we derive a formula connecting the lattice three-point function to the CP-odd electromagnetic form factor. In the second method we directly extract the NEDM from the energy difference between spin-up and spin-down neutron states in the presence of a constant electric field, without expanding a small but non-zero $θ$. We test both approaches numerically, employing the domain-wall quark action with the RG improved gauge action in quenched QCD at $a^{-1}\simeq 2$ GeV on a $16^3\times 32\times 16$ lattice, and further applying the second method to the clover quark action at a similar lattice spacing and nucleon mass. We obtain good signals from both approaches. In particular the second method works well with both fermion formulations.
6 pages, 7 eps-figures, talk presented at Lattice 2005 (Chiral fermions), Trinity College, Dublin, Ireland, 25-30 Jul 2005