24,760 research outputs found
Finite Temperature Phase Diagramm of QCD with improved Wilson fermions
We present first results of a study of two flavour QCD with Wilson fermions
at finite temperature. We have used tree level Symanzik improvement in both the
gauge and fermion part of the action. In a first step we explore the phase
diagramm on an lattice, with particular emphasis on checking
Aoki's conjecture with an improved action.Comment: Talk presented at LATTICE97(finite temperature), 3 pages, 3
Postscript figure
Operator product expansion and the short distance behavior of 3-flavor baryon potentials
The short distance behavior of baryon-baryon potentials defined through
Nambu-Bethe-Salpeter wave functions is investigated using the operator product
expansion. In a previous analysis of the nucleon-nucleon case, corresponding to
the SU(3) channels and , we argued that the potentials
have a repulsive core. A new feature occurs for the case of baryons made up of
three flavors: manifestly asymptotically attractive potentials appear in the
singlet and octet channels. Attraction in the singlet channel was first
indicated by quark model considerations, and recently been found in numerical
lattice simulations. The latter have however not yet revealed asymptotic
attraction in the octet channels; we give a speculative explanation for this
apparent discrepancy.Comment: 11 pages, 2 figure
Structure of Critical Lines in Quenched Lattice QCD with the Wilson Quark Action
The structure of critical lines of vanishing pion mass for the Wilson quark
action is examined in quenched lattice QCD. The numerical evidence is presented
that critical lines spread into five branches beyond beta=5.6-5.7 at zero
temperature. It is also shown that critical lines disappear in the deconfined
phase for the case of finite temperatures.Comment: 11 pages, Latex, 7 Postscript figures, uses epsf.st
Some aspects of control of a large-scale dynamic system
Techniques of predicting and/or controlling the dynamic behavior of large scale systems are discussed in terms of decentralized decision making. Topics discussed include: (1) control of large scale systems by dynamic team with delayed information sharing; (2) dynamic resource allocation problems by a team (hierarchical structure with a coordinator); and (3) some problems related to the construction of a model of reduced dimension
Chemical Abundances of the Outer Halo Stars in the Milky Way
We present chemical abundances of 57 metal-poor stars that are likely
constituents of the outer stellar halo in the Milky Way. Almost all of the
sample stars have an orbit reaching a maximum vertical distance (Z_max) of >5
kpc above and below the Galactic plane. High-resolution, high signal-to-noise
spectra for the sample stars obtained with Subaru/HDS are used to derive
chemical abundances of Na, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y and Ba with an LTE
abundance analysis code. The resulting abundance data are combined with those
presented in literature that mostly targeted at smaller Z_max stars, and both
data are used to investigate any systematic trends in detailed abundance
patterns depending on their kinematics. It is shown that, in the metallicity
range of -25 kpc are
systematically lower (~0.1 dex) than those with smaller Z_max. This result of
the lower [alpha/Fe] for the assumed outer halo stars is consistent with
previous studies that found a signature of lower [alpha/Fe] ratios for stars
with extreme kinematics. A distribution of the [Mg/Fe] ratios for the outer
halo stars partly overlaps with that for stars belonging to the Milky Way dwarf
satellites in the metallicity interval of -2<[Fe/H]<-1 and spans a range
intermediate between the distributions for the inner halo stars and the stars
belonging to the satellites. Our results confirm inhomogeneous nature of
chemical abundances within the Milky Way stellar halo depending on kinematic
properties of constituent stars as suggested by earlier studies. Possible
implications for the formation of the Milky Way halo and its relevance to the
suggested dual nature of the halo are discussed.Comment: 68 pages with 23 figures, Accepted for publication in PAS
Spontaneous Flavor and Parity Breaking with Wilson Fermions
We discuss the phase diagram of Wilson fermions in the -- plane for
two-flavor QCD. We argue that, as originally suggested by Aoki, there is a
phase in which flavor and parity are spontaneously broken. Recent numerical
results on the spectrum of the overlap Hamiltonian have been interpreted as
evidence against Aoki's conjecture. We show that they are in fact consistent
with the presence of a flavor-parity broken ``Aoki phase''. We also show how,
as the continuum limit is approached, one can study the lattice theory using
the continuum chiral Lagrangian supplemented by additional terms proportional
to powers of the lattice spacing. We find that there are two possible phase
structures at non-zero lattice spacing: (1) there is an Aoki phase of width
with two massless Goldstone pions; (2) there is no
symmetry breaking, and all three pions have an equal non-vanishing mass of
order . Present numerical evidence suggests that the former option is
realized for Wilson fermions. Our analysis then predicts the form of the pion
masses and the flavor-parity breaking condensate within the Aoki phase. Our
analysis also applies for non-perturbatively improved Wilson fermions.Comment: 22 pages, LaTeX, 5 figures (added several references and a comment
Tau polarization effects in the CNGS tau-neutrino appearance experiments
We studied tau polarization effects on the decay distributions of tau
produced in the CNGS tau-neutrino appearance experiments. We show that energy
and angular distributions for the decay products in the laboratory frame are
significantly affected by the tau polarization. Rather strong azimuthal
asymmetry about the tau momentum axis is predicted, which may have observable
consequences in experiments even with small statistics.Comment: 5 pages, 6 eps figures, espcrc2.sty; Proceedings of the 4th
International Workshop on Neutrino-Nucleus Interactions in the Few GeV Region
(NuInt05), September 26-29, 2005, Okayama, Japa
Passing through the `chiral limit' in quenched QCD with Wilson fermions
We investigate the limit of vanishing quark mass in quenched lattice QCD with
unimproved Wilson fermions at . Exploiting the correlations of
propagators at different time slices we extract pion masses extremely close to
the `chiral limit', despite the presence of `exceptional configurations'. With
this at hand, the existence of quenched chiral logarithms can be demonstrated,
provided, finite size effects are small. With reference to the phase diagram
proposed by Aoki also the range is investigated. The width
of a potential parity-flavor violating phase can, if at all, hardly be
resolved.Comment: LATTICE98(spectrum
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