514 research outputs found
Electromagnetic Structure of Light Baryons in Lattice QCD
A method in which electromagnetic properties of hadrons are studied by direct
simulation of dynamical photon effects is applied to the extraction of the
isomultiplet structure of the octet baryons. Using 187 configurations at
with Wilson action, and up and down quark masses determined from
the meson spectrum, the nucleon splitting is found to be MeV; the hyperon splittings are found to be
, ,
MeV. Estimated systematic corrections arising
from finite volume and the quenched approximation are included in these
results.Comment: Talk presented at LATTICE96(phenomenology
Z Boson Propagator Correction in Technicolor Theories with ETC Effects Included
We calculate the Z boson propagator correction, as described by the S
parameter, in technicolor theories with extended technicolor interactions
included. Our method is to solve the Bethe-Salpeter equation for the requisite
current-current correlation functions. Our results suggest that the inclusion
of extended technicolor interactions has a relatively small effect on S.Comment: 15pages, 8 figure
Equation of State for physical quark masses
We calculate the QCD equation of state for temperatures corresponding to the
transition region with physical mass values for two degenerate light quark
flavors and a strange quark using an improved staggered fermion action
(p4-action) on lattices with temporal extent N_tau=8. We compare our results
with previous calculations performed at twice larger values of the light quark
masses as well as with results obtained from a resonance gas model calculation.
We also discuss the deconfining and chiral aspects of the QCD transition in
terms of renormalized Polyakov loop, strangeness fluctuations and subtracted
chiral condensate. We show that compared to the calculations performed at twice
larger value of the light quark mass the transition region shifts by about 5
MeV toward smaller temperaturesComment: 7 pages, LaTeX, 6 figures; minor corrections, typos corrected,
references adde
Chirality Correlation within Dirac Eigenvectors from Domain Wall Fermions
In the dilute instanton gas model of the QCD vacuum, one expects a strong
spatial correlation between chirality and the maxima of the Dirac eigenvectors
with small eigenvalues. Following Horvath, {\it et al.} we examine this
question using lattice gauge theory within the quenched approximation. We
extend the work of those authors by using weaker coupling, , larger
lattices, , and an improved fermion formulation, domain wall fermions. In
contrast with this earlier work, we find a striking correlation between the
magnitude of the chirality density, , and the
normal density, , for the low-lying Dirac eigenvectors.Comment: latex, 25 pages including 12 eps figure
The Spatial String Tension and Dimensional Reduction in QCD
We calculate the spatial string tension in (2+1) flavor QCD with physical
strange quark mass and almost physical light quark masses using lattices with
temporal extent N_tau=4,6 and 8. We compare our results on the spatial string
tension with predictions of dimensionally reduced QCD. This suggests that also
in the presence of light dynamical quarks dimensional reduction works well down
to temperatures 1.5T_c.Comment: 8 pages ReVTeX, 4 figure
Chiral corrections to the axial charges of the octet baryons from quenched QCD
We calculate one-loop correction to the axial charges of the octet baryons
using quenched chiral perturbation theory, in order to understand chiral
behavior of the axial charges in quenched approximation to quantum
chromodynamics (QCD). In contrast to regular behavior of the full QCD chiral
perturbation theory result, , we find
that the quenched chiral perturbation theory result,
, is
singular in the chiral limit.Comment: standard LaTeX, 16 pages, 4 epsf figure
Study of the finite temperature transition in 3-flavor QCD using the R and RHMC algorithms
We study the finite temperature transition in QCD with three flavors of equal
masses using the R and RHMC algorithm on lattices with temporal extent
N_{\tau}=4 and 6. For the transition temperature in the continuum limit we find
r_0 T_c=0.429(8) for the light pseudo-scalar mass corresponding to the end
point of the 1st order transition region. When comparing the results obtained
with the R and RHMC algorithms for p4fat3 action we see no significant
step-size errors down to a lightest pseudo-scalar mass of m_{ps} r_0=0.4.Comment: 13 pages, RevTeX, 10 figure
Continuum Limit of from 2+1 Flavor Domain Wall QCD
We determine the neutral kaon mixing matrix element in the continuum
limit with 2+1 flavors of domain wall fermions, using the Iwasaki gauge action
at two different lattice spacings. These lattice fermions have near exact
chiral symmetry and therefore avoid artificial lattice operator mixing.
We introduce a significant improvement to the conventional NPR method in
which the bare matrix elements are renormalized non-perturbatively in the
RI-MOM scheme and are then converted into the MSbar scheme using continuum
perturbation theory. In addition to RI-MOM, we introduce and implement four
non-exceptional intermediate momentum schemes that suppress infrared
non-perturbative uncertainties in the renormalization procedure. We compute the
conversion factors relating the matrix elements in this family of RI-SMOM
schemes and MSbar at one-loop order. Comparison of the results obtained using
these different intermediate schemes allows for a more reliable estimate of the
unknown higher-order contributions and hence for a correspondingly more robust
estimate of the systematic error. We also apply a recently proposed approach in
which twisted boundary conditions are used to control the Symanzik expansion
for off-shell vertex functions leading to a better control of the
renormalization in the continuum limit.
We control chiral extrapolation errors by considering both the NLO SU(2)
chiral effective theory, and an analytic mass expansion. We obtain
B_K^{\msbar}(3 GeV) = 0.529(5)_{stat}(15)_\chi(2)_{FV}(11)_{NPR}. This
corresponds to . Adding
all sources of error in quadrature we obtain , with an overall combined error of 3.6%.Comment: 65 page
The Decay Amplitude from Lattice QCD
We report on the first realistic \emph{ab initio} calculation of a hadronic
weak decay, that of the amplitude for a kaon to decay into two \pi-mesons
with isospin 2. We find Re in good agreement with the
experimental result and for the hitherto unknown imaginary part we find
{Im}. Moreover combining our result for
Im\, with experimental values of Re\,, Re\, and
, we obtain the following value for the unknown ratio
Im\,/Re\, within the Standard Model:
.
One consequence of these results is that the contribution from Im\, to the
direct CP violation parameter (the so-called Electroweak
Penguin, EWP, contribution) is Re. We
explain why this calculation of represents a major milestone for lattice
QCD and discuss the exciting prospects for a full quantitative understanding of
CP-violation in kaon decays.Comment: 5 pages, 1 figur
The transition temperature in QCD
We present a detailed calculation of the transition temperature in QCD with
two light and one heavier (strange) quark mass on lattices with temporal extent
N_t =4 and 6. Calculations with improved staggered fermions have been performed
for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <=
0.5, and with a strange quark mass fixed close to its physical value. From a
combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0)
limits we find for the transition temperature at the physical point T_c r_0 =
0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as
the distance in the static quark potential at which the slope takes on the
value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. Using the currently best known value
for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. The
transition temperature in the chiral limit is about 3% smaller. We discuss
current ambiguities in the determination of T_c in physical units and also
comment on the universal scaling behavior of thermodynamic quantities in the
chiral limit.Comment: 18 pages, 14 EPS figures, replaced wrong entries in column 7 of Table
A.
- …