138 research outputs found
Thermodynamic properties of QCD with two flavors of Wilson-type lattice quarks
I report on a study of finite temperature QCD by the CP-PACS Collaboration
toward a precise determination of the equation of state with dynamical u,d
quarks. Based on a systematic simulation using improved Wilson-type quarks on
lattices with temporal size and 6, the energy density and pressure are
calculated as functions of temperature and renormalized light quark mass in the
range --2.5 and --0.95. Results
for are found to contain significant scaling violations, while results
for are suggested to be not far from the continuum limit. On the other
hand, the quark mass dependence in the EOS turned out to be small for m_{\rm
PS}/m_{\rm V} \simlt 0.8.Comment: Talk presented at Statistical QCD, Aug. 26-30, 2001, Bielefeld,
Germany. LaTeX2e, 6 pages, 4 PS figures, espcrc1.sty neede
New results on cut-off effects in spectroscopy with the fixed point action
Our study on the cut-off effects in quenched light hadron spectroscopy and
pion scattering length with the fixed point action is extended by results
obtained at a lattice spacing a=0.102 fm in a box of size L=1.8 fm. The cut-off
effects are small, but clearly seen as the resolution is increased from a=0.153
fm to a=0.102 fm. In the quark mass region where the errors are small and under
control, our results on the APE plot lie close to the extrapolated numbers of
the CP-PACS Collaboration.Comment: 15 pages, 11 figures, reference correcte
Strange quark mass from Finite Energy QCD sum rules to five loops
The strange quark mass is determined from a new QCD Finite Energy Sum Rule
(FESR) optimized to reduce considerably the systematic uncertainties arising
from the hadronic resonance sector. As a result, the main uncertainty in this
determination is due to the value of . The correlator of
axial-vector divergences is used in perturbative QCD to five-loop order,
including quark and gluon condensate contributions, in the framework of both
Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter
exhibits very good convergence, leading to a remarkably stable result in the
very wide range , where is the radius of the
integration contour in the complex energy (squared) plane. The value of the
strange quark mass in this framework at a scale of 2 GeV is for , respectively.Comment: Additional comments added at the end of the Conclusions, and one
extra reference is given. A note added in proof uses the most recent
determination of Lambda_QCD from ALEPH to narrow down the predictio
Lattice QCD and the Schwarz alternating procedure
A numerical simulation algorithm for lattice QCD is described, in which the
short- and long-distance effects of the sea quarks are treated separately. The
algorithm can be regarded, to some extent, as an implementation at the quantum
level of the classical Schwarz alternating procedure for the solution of
elliptic partial differential equations. No numerical tests are reported here,
but theoretical arguments suggest that the algorithm should work well also at
small quark masses.Comment: Plain TeX source, 20 pages, figures include
Flavour structure and proton decay in 6D orbifold GUTs
We study proton decay in a supersymmetric {\sf SO(10)} gauge theory in six
dimensions compactified on an orbifold. The dimension-5 proton decay operators
are forbidden by R-symmetry, whereas the dimension-6 operators are enhanced due
to the presence of KK towers. Three sequential quark-lepton families are
localised at the three orbifold fixed points, where {\sf SO(10)} is broken to
its three GUT subgroups. The physical quarks and leptons are mixtures of these
brane states and additional bulk zero modes. This leads to a characteristic
pattern of branching ratios in proton decay, in particular the suppression of
the p\to \m^+K^0 mode.Comment: 20 pages, 1 figur
Twisted mass QCD and lattice approaches to the rule
Twisted mass lattice QCD (tmQCD), generalised to four Wilson quark flavours,
can be used for the computation of some weak matrix elements related to transitions. Besides eliminating unphysical zero modes, tmQCD may
alleviate long-standing renormalisation problems of the four-quark operators
which contribute to CP-conserving transitions. With an active charm
quark, the renormalisation of the matrix elements requires at most
the subtraction of a linearly divergent counterterm. Furthermore, in the
(partially) quenched approximation the twist angles can be chosen so that only
a finite counterterm needs to be subtracted.Comment: 35 pages;final version with references adde
Charmed meson spectra and decay constants with one-loop improved relativistic heavy quark action
We calculate charmed meson spectra and decay constants in lattice QCD
employing one-loop improved heavy quark action and axial-vector
currents. In quenched simulations at fm with the plaquette gauge
action as well as a renormalization-group improved one, it is shown that the
deviation from the continuum dispersion relation and the violation of
space-time symmetry for the pseudoscalar meson decay constants are
substantially reduced, once the improvement is applied. Preliminary
results with two flavors of dynamical quarks are also presented.Comment: 3 pages, 4 figure, talk presented at Lattice2004(heavy), Fermilab,
June 21-26, 200
Chirally improving Wilson fermions - I. O(a) improvement
We show that it is possible to improve the chiral behaviour and the approach
to the continuum limit of correlation functions in lattice QCD with Wilson
fermions by taking arithmetic averages of correlators computed in theories
regularized with Wilson terms of opposite sign. Improved hadronic masses and
matrix elements can be obtained by similarly averaging the corresponding
physical quantities separately computed within the two regularizations. To deal
with the problems related to the spectrum of the Wilson--Dirac operator, which
are particularly worrisome when Wilson and mass terms are such as to give
contributions of opposite sign to the real part of the eigenvalues, we propose
to use twisted-mass lattice QCD for the actual computation of the quantities
taking part to the averages. The choice for the twisting angle is
particularly interesting, as O() improved estimates of physical quantities
can be obtained even without averaging data from lattice formulations with
opposite Wilson terms. In all cases little or no extra computing power is
necessary, compared to simulations with standard Wilson fermions or
twisted-mass lattice QCD.Comment: 71 pages, Latex, Keywords: Lattice, Improvement, Chirality. Version
v2: mistake corrected in transformation properties under \omega -> -\omega,
sect. 5.3.1 (see also sect. 6.1). Minor corrections in App. D and argument
clarified in App. F. Version v3: minor modifications in sect. 2 (pag. 8-10:
on the odd r-parity of M_crit(r)), in sect. 3.1.3 and 5.4.1 (few sentences
about cutoff effects at small quark mass) and in sect. 3.2 (details of
discussion below eq. 3.17); updated/added some reference
Sea quark effects in B_K from N_f=2 clover-improved Wilson fermions
We report calculations of the parameter B_K appearing in the Delta S=2
neutral kaon mixing matrix element, whose uncertainty limits the power of
unitarity triangle constraints for testing the standard model or looking for
new physics. We use two flavours of dynamical clover-improved Wilson lattice
fermions and look for dependence on the dynamical quark mass at fixed lattice
spacing. We see some evidence for dynamical quark effects and in particular B_K
decreases as the sea quark masses are reduced towards the up/down quark mass.Comment: 17 pages, 4 figures, uses JHEP3.cls, added comments and reference
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