442 research outputs found
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
Two-Nucleon Bound States in Quenched Lattice QCD
We address the issue of bound state in the two-nucleon system in lattice QCD.
Our study is made in the quenched approximation at the lattice spacing of a =
0.128 fm with a heavy quark mass corresponding to m_pi = 0.8 GeV. To
distinguish a bound state from an attractive scattering state, we investigate
the volume dependence of the energy difference between the ground state and the
free two-nucleon state by changing the spatial extent of the lattice from 3.1
fm to 12.3 fm. A finite energy difference left in the infinite spatial volume
limit leads us to the conclusion that the measured ground states for not only
spin triplet but also singlet channels are bounded. Furthermore the existence
of the bound state is confirmed by investigating the properties of the energy
for the first excited state obtained by 2x2 diagonalization method. The
scattering lengths for both channels are evaluated by applying the finite
volume formula derived by Luscher to the energy of the first excited states.Comment: 34 pages, 28 figure
Pion-Nucleon Sigma Term in Lattice QCD
We calculate both connected and disconnected contribution to the -
-term in quenched lattice QCD with Wilson quark action on a lattice at . The latter is evaluated with the aid of the variant
wall source method, which was previously applied successfully for extraction of
- scattering lengths and meson mass. We found that the
disconnected contribution is about twice larger than the connected one. The
value for the full - term MeV is consistent
with the experimental estimates. The nucleon matrix element of the strange
quark density is fairly large in our result.Comment: 11 pages. Latex file. Figures are also included as ps file
An Exploratory Study of Nucleon-Nucleon Scattering Lengths in Lattice QCD
An exploratory study is made of the nucleon-nucleon -wave scattering
lengths in quenched lattice QCD with the Wilson quark action. The - and
- scattering lengths are also calculated for comparison. The
calculations are made with heavy quarks corresponding to . The results show that the - system has an attractive force in
both spin-singlet and triplet channels, with their scattering lengths
significantly larger than those for the - and - cases, a
trend which is qualitatively consistent with the experiment. Problems toward a
more realistic calculation for light quarks are discussed.Comment: 9 pages. Latex file. Figures are also included as ps file
Lattice QCD with Domain-Wall Fermions
We study the quenched lattice QCD using domain-wall fermions at .
Behaviors of both pion mass and the explicit breaking term in the axial
Ward-Takahashi identity support the existence of the chiral zero modes. We
observe a good agreement between the pion decay constants from both the
conserved axial current and the local current perturbatively renormalized at
1-loop. Finally the possible existence of the parity broken phase is also
examined in this model.Comment: LATTICE99 (Chiral Fermions), 3 page
Continuum limit of proton decay matrix elements in quenched lattice QCD
We present a lattice QCD calculation of the parameters \alpha and \beta which
are necessary in the theoretical estimation of the proton lifetime in grand
unified theories (GUTs) using chiral lagrangian approach. The simulation is
carried out using the Wilson quark action at three gauge coupling constants in
the quenched approximation. We obtain
|\alpha(2GeV)|=0.0091(08)(^{+10}_{-19})GeV^3 and
|\beta(2GeV)|=0.0098(08)(^{+10}_{-20})GeV^3 in the continuum limit where the
first error is statistical and the second one is due to scale setting.Comment: 3 pages, 2 figures, talk presented at Lattice2003(matrix
Finite-volume two-pion energies and scattering in the quenched approximation
We investigate how L\"uscher's relation between the finite-volume energy of
two pions at rest and pion scattering lengths has to be modified in quenched
QCD. We find that this relation changes drastically, and in particular, that
``enhanced finite-volume corrections" of order and occur at
one loop ( is the linear size of the box), due to the special properties of
the in the quenched approximation. We define quenched pion scattering
lengths, and show that they are linearly divergent in the chiral limit. We
estimate the size of these various effects in some numerical examples, and find
that they can be substantial.Comment: 22 pages, uuencoded, compressed postscript fil
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