1,659 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
Solvable Discrete Quantum Mechanics: q-Orthogonal Polynomials with |q|=1 and Quantum Dilogarithm
Several kinds of q-orthogonal polynomials with |q|=1 are constructed as the
main parts of the eigenfunctions of new solvable discrete quantum mechanical
systems. Their orthogonality weight functions consist of quantum dilogarithm
functions, which are a natural extension of the Euler gamma functions and the
q-gamma functions (q-shifted factorials). The dimensions of the orthogonal
spaces are finite. These q-orthogonal polynomials are expressed in terms of the
Askey-Wilson polynomials and their certain limit forms.Comment: 37 pages. Comments and references added. To appear in J.Math.Phy
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
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
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.
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