1,280 research outputs found
Intra-Landau level polarization effect for a striped Hall gas
We calculate the polarization function including only intra-Landau level
correlation effects of striped Hall gas. Using the polarization function, the
dielectric function, the dispersion of the plasmon and the correlation energy
are computed in a random phase approximation (RPA) and generalized random phase
approximation (GRPA). The plasmon becomes anisotropic and gapless owing to the
anisotropy of the striped Hall gas and two dimensionality of the quantum Hall
system. The plasmon approximately agrees with the phonon derived before by the
single mode approximation. The (G)RPA correlation energy is compared with other
numerical calculations.Comment: 15 pages,15 figures, revtex4, published versio
Pion decay constant for the Kogut-Susskind quark action in quenched lattice QCD
We present a study for the pion decay constant in the quenched
approximation to lattice QCD with the Kogut-Susskind (KS) quark action, with
the emphasis given to the renormalization problems. Numerical simulations are
carried out at the couplings and 6.2 on and
lattices, respectively. The pion decay constant is evaluated
for all KS flavors via gauge invariant and non-invariant axial vector currents
with the renormalization constants calculated by both non-perturbative method
and perturbation theory. We obtain MeV in the continuum limit
as the best value using the partially conserved axial vector current, which
requires no renormalization. From a study for the other KS flavors we find that
the results obtained with the non-perturbative renormalization constants are
well convergent among the KS flavors in the continuum limit, confirming
restoration of flavor symmetry, while perturbative
renormalization still leaves an apparent flavor breaking effect even in the
continuum limit.Comment: LaTex, 27 pages, 35 eps figures, uses revtex and eps
Lattice QCD Calculation of the Kaon B-parameter with the Wilson Quark Action
The kaon B parameter is calculated in quenched lattice QCD with the Wilson
quark action. The mixing problem of the \Delta s=2 four-quark operators is
solved non-perturbatively with full use of chiral Ward identities, and this
method enables us to construct the weak four-quark operators exhibiting good
chiral behavior. We find B_K(NDR, 2GeV)=0.562(64) in the continuum limit, which
agrees with the value obtained with the Kogut-Susskind quark action.Comment: 11 pages, latex source-file, 4 figures as ps-fil
Light hadron spectroscopy in two-flavor QCD with small sea quark masses
We extend the study of the light hadron spectrum and the quark mass in
two-flavor QCD to smaller sea quark mass, corresponding to
--0.35. Numerical simulations are carried out using the
RG-improved gauge action and the meanfield-improved clover quark action at
( fm from meson mass). We observe that the light
hadron spectrum for small sea quark mass does not follow the expectation from
chiral extrapolations with quadratic functions made from the region of
--0.55. Whereas fits with either polynomial or continuum
chiral perturbation theory (ChPT) fails, the Wilson ChPT (WChPT) that includes
effects associated with explicit chiral symmetry breaking successfully
fits the whole data: In particular, WChPT correctly predicts the light quark
mass spectrum from simulations for medium heavy quark mass, such as m_{PS}/m_V
\simgt 0.5. Reanalyzing the previous data %at --0.55 with
the use of WChPT, we find the mean up and down quark mass being smaller than
the previous result from quadratic chiral extrapolation by approximately 10%,
[MeV] in the continuum limit.Comment: 33 page
Partial Flavor Symmetry Restoration for Chiral Staggered Fermions
We study the leading discretization errors for staggered fermions by first
constructing the continuum effective Lagrangian including terms of O(a^2), and
then constructing the corresponding effective chiral Lagrangian. The terms of
O(a^2) in the continuum effective Lagrangian completely break the SU(4) flavor
symmetry down to the discrete subgroup respected by the lattice theory. We
find, however, that the O(a^2) terms in the potential of the chiral Lagrangian
maintain an SO(4) subgroup of SU(4). It follows that the leading discretization
errors in the pion masses are SO(4) symmetric, implying three degeneracies
within the seven lattice irreducible representations. These predictions hold
also for perturbatively improved versions of the action. These degeneracies are
observed, to a surprising degree of accuracy, in existing data. We argue that
the SO(4) symmetry does not extend to the masses and interactions of other
hadrons (vector mesons, baryons, etc), nor to higher order in a^2. We show how
it is possible that, for physical quark masses of O(a^2), the new SO(4)
symmetry can be spontaneously broken, leading to a staggered analogue of the
Aoki-phase of Wilson fermions. This does not, however, appear to happen for
presently studied versions of the staggered action.Comment: 26 pages, 2 figures (using psfig). Version to appear in PRD
(clarifications added to introduction and section 6; typos corrected;
references updated
One Spin Trace Formalism for
It has been known for some time that there are two methods to calculate with staggered fermions: one is the two spin trace formalism and the other is
the one spin trace formalism. Until now, the two spin trace formalism has been
exclusively used for weak matrix element calculations with staggered fermions.
Here, the one spin trace formalism to calculate with staggered fermions
is explained. It is shown that the one spin trace operators require additional
chiral partner operators in order to keep the continuum chiral behavior. The
renormalization of the one spin trace operators is described and compared with
the two spin trace formalism.Comment: 47 pages, latex, 4 figures are available on reques
Exchange coupling in Eu monochalcogenides from first principles
Using a density functional method with explicit account for strong Coulomb
repulsion within the 4f shell, we calculate effective exchange parameters and
the corresponding ordering temperatures of the (ferro)magnetic insulating Eu
monochalcogenides (EuX; X=O,S,Se,Te) at ambient and elevated pressure
conditions. Our results provide quantitative account of the many-fold increase
of the Curie temperatures with applied pressure and reproduce well the
enhancement of the tendency toward ferromagnetic ordering across the series
from telluride to oxide, including the crossover from antiferromagnetic to
ferromagnetic ordering under pressure in EuTe and EuSe. The first and second
neighbor effective exchange are shown to follow different functional
dependencies. Finally, model calculations indicate a significant contribution
of virtual processes involving the unoccupied f states to the effective
exchange.Comment: 4 pages, 6 figure
Solar neutrino results in Super-Kamiokande-III
The results of the third phase of the Super-Kamiokande solar neutrino
measurement are presented and compared to the first and second phase results.
With improved detector calibrations, a full detector simulation, and improved
analysis methods, the systematic uncertainty on the total neutrino flux is
estimated to be ?2.1%, which is about two thirds of the systematic uncertainty
for the first phase of Super-Kamiokande. The observed 8B solar flux in the 5.0
to 20 MeV total electron energy region is 2.32+/-0.04 (stat.)+/-0.05 (sys.)
*10^6 cm^-2sec^-1, in agreement with previous measurements. A combined
oscillation analysis is carried out using SK-I, II, and III data, and the
results are also combined with the results of other solar neutrino experiments.
The best-fit oscillation parameters are obtained to be sin^2 {\theta}12 =
0.30+0.02-0.01(tan^2 {\theta}12 = 0.42+0.04 -0.02) and {\Delta}m2_21 =
6.2+1.1-1.9 *10^-5eV^2. Combined with KamLAND results, the best-fit oscillation
parameters are found to be sin^2 {\theta}12 = 0.31+/-0.01(tan^2 {\theta}12 =
0.44+/-0.03) and {\Delta}m2_21 = 7.6?0.2*10^-5eV^2 . The 8B neutrino flux
obtained from global solar neutrino experiments is
5.3+/-0.2(stat.+sys.)*10^6cm^-2s^-1, while the 8B flux becomes
5.1+/-0.1(stat.+sys.)*10^6cm^-2s^-1 by adding KamLAND result. In a three-flavor
analysis combining all solar neutrino experiments, the upper limit of sin^2
{\theta}13 is 0.060 at 95% C.L.. After combination with KamLAND results, the
upper limit of sin^2 {\theta}13 is found to be 0.059 at 95% C.L..Comment: 19 pages, 33 figures in the main text. The appendix section on errata
is added in v
The Kaon B-parameter with the Wilson Quark Action using Chiral Ward Identities
A lattice QCD calculation of the kaon parameter is carried out with
the Wilson quark action in the quenched approximation at .
The mixing problem of the four-quark operators is solved
non-perturbatively with full use of chiral Ward identities employing four
external quarks with an equal off-shell momentum in the Landau gauge. This
method, without invoking any effective theory, enables us to construct the weak
four-quark operators exhibiting good chiral behavior. Our results for
with the non-perturbative mixing coefficients show small scaling violation
beyond the lattice cut-off GeV. Our estimate concludes
at GeV, which agrees with the value
obtained with the Kogut-Susskind quark action. For comparison we also calculate
with one-loop perturbative mixing coefficients. While this yields
incorrect values at finite lattice spacing, a linear extrapolation to the
continuum limit as a function of leads to a result consistent with those
obtained with the Ward identity method.Comment: 42 pages, 22 Postscript figures, added a new reference[26
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