出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present a study of the neutron electric dipole moment (~dN) within the framework of lattice
QCD with two flavors of light quarks. The dipole moment is sensitive to the topological structure
of the gauge fields, so accuracy can only be achieved by using dynamical, or sea quark, calculations.
The topological charge (distribution) evolves slowly in these calculations, leading to
systematic uncertainty in ~dN. It is shown, using quenched configurations, that a better sampling
of the charge distribution eliminates this problem, but because the CP even part of the fermion
determinant is absent, both the topological charge distribution and ~dN are pathological in the chiral
limit. We discuss the systematic uncertainties arising from the topological charge distribution
and unphysical quark mass in our calculations and prospects for eliminating them.
Our calculations are done using two flavors of domain wall fermions and the DBW2 gauge action
with inverse lattice spacing a−1 1.7 GeV, physical volume V (2 fm)3, and light quark
mass roughly equal to the strange quark mass. The systematic uncertainties described above
notwithstanding, we find |~dN|=10(11)×10−15 eq cm. The central value translates into the bound
q <6.3×10−11 on the fundamental CP-odd parameter in the QCD lagrangian when combined
with the current experimental bound on |~dN|. The quoted error is statistical only. Satisfactory results
for the magnetic dipole moments and electromagnetic form factors of the proton and neutron
are also obtained.
