2,321 research outputs found
Neutron electric dipole moment with external electric field method in lattice QCD
We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can
be calculated in lattice QCD simulations in the presence of the CP violating
term. In this paper we measure the energy difference between spin-up
and spin-down states of the neutron in the presence of an uniform and static
external electric field. We first test this method in quenched QCD with the RG
improved gauge action on a lattice at 2 GeV,
employing two different lattice fermion formulations, the domain-wall fermion
and the clover fermion for quarks, at relatively heavy quark mass . We obtain non-zero values of NEDM from calculations with both
fermion formulations. We next consider some systematic uncertainties of our
method for NEDM, using lattice at the same lattice spacing only
with the clover fermion. We finally investigate the quark mass dependence of
NEDM and observe a non-vanishing behavior of NEDM toward the chiral limit. We
interpret this behavior as a manifestation of the pathology in the quenched
approximation.Comment: LaTeX2e, 51 pages, 43 figures, uses revtex4 and graphicx, References
and comments added, typos corrected, accepted by PR
Electromagnetic and spin polarisabilities in lattice QCD
We discuss the extraction of the electromagnetic and spin polarisabilities of
nucleons from lattice QCD. We show that the external field method can be used
to measure all the electromagnetic and spin polarisabilities including those of
charged particles. We then turn to the extrapolations required to connect such
calculations to experiment in the context of finite volume chiral perturbation
theory. We derive results relevant for lattice simulations of QCD,
partially-quenched QCD and quenched QCD. Our results for the polarisabilities
show a strong dependence on the lattice volume and quark masses, typically
differing from the infinite volume limit by ~10% for current lattice volumes
and quark masses.Comment: Minor change
Lattice study of vacuum polarization function and determination of strong coupling constant
We calculate the vacuum polarization functions on the lattice using the
overlap fermion formulation.By matching the lattice data at large momentum
scales with the perturbative expansion supplemented by Operator Product
Expansion (OPE), we extract the strong coupling constant in
two-flavor QCD as =
GeV, where the errors are statistical and systematic, respectively. In
addition, from the analysis of the difference between the vector and
axial-vector channels, we obtain some of the four-quark condensates.Comment: 24 pages, 9 figures, enlarged version published in Phys. Rev.
Two-photon decay of the neutral pion in lattice QCD
We perform non-perturbative calculation of the \pi^0 to {\gamma}{\gamma}
transition form factor and the associated decay width using lattice QCD. The
amplitude for two-photon final state, which is not an eigenstate of QCD, is
extracted through an Euclidean time integral of the relevant three-point
function. We utilize the all-to-all quark propagator technique to carry out
this integral as well as to include the disconnected quark diagram
contributions. The overlap fermion formulation is employed on the lattice to
ensure exact chiral symmetry on the lattice. After examining various sources of
systematic effects except for possible discretization effect, we obtain
\Gamma=7.83(31)(49) eV for the pion decay width, where the first error is
statistical and the second is our estimate of the systematic error.Comment: 5 pages, 4 figures. Changes made addressing to referee's comments,
version accepted by PR
Strong coupling constant from vacuum polarization functions in three-flavor lattice QCD with dynamical overlap fermions
We determine the strong coupling constant from a lattice
calculation of vacuum polarization functions (VPF) in three-flavor QCD with
dynamical overlap fermions. Fitting lattice data of VPF to the continuum
perturbative formula including the operator product expansion, we extract the
QCD scale parameter . At the boson mass
scale, we obtain , where the first
error is statistical and the second is our estimate of various systematic
uncertainties.Comment: 15 pages, 7 figures, references updated. After correction of error in
code, final value is changed, see Erratum Phys.Rev.D89,099903 (2014
Full QCD calculation of neutron electric dipole moment with the external electric field method
We have calculated the neutron electric dipole moment (NEDM) in the presence
of the CP violating term in lattice QCD with 2-flavor dynamical clover
quarks, using the external electric field method. Accumulating a large number
of statistics by the averages over 16 different source points and over forward
and backward nucleon propagators, we have obtained non-zero signals of neutron
and proton EDM beyond one standard deviation at each quark mass in full QCD. We
have investigated the quark mass dependence of nucleon EDM in full QCD, and
have found that nucleon EDM in full QCD does not decrease toward the chiral
limit, as opposed to the theoretical expectation. We briefly discuss possible
reasons for this behavior.Comment: 27 pages, 15 figures, 2 tables, reference added, tyops corrected,
published versio
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