1,257 research outputs found
Spectra of massive QCD dirac operators from random matrix theory: All three chiral symmetry breaking patterns
The microscopic spectral eigenvalue correlations of QCD Dirac operators in the presence of dynamical fermions are calculated within the framework of Random Matrix Theory (RMT). Our approach treats the low-energy correlation functions of all three chiral symmetry breaking patterns (labeled by the Dyson index ÎČ = 1, 2 and 4) on the same footing, offering a unifying description of massive QCD Dirac spectra. RMT universality is explicitly proven for all three symmetry classes and the results are compared to the available lattice data for ÎČ = 4
Universal and non-universal behavior in Dirac spectra
We have computed ensembles of complete spectra of the staggered Dirac
operator using four-dimensional SU(2) gauge fields, both in the quenched
approximation and with dynamical fermions. To identify universal features in
the Dirac spectrum, we compare the lattice data with predictions from chiral
random matrix theory for the distribution of the low-lying eigenvalues. Good
agreement is found up to some limiting energy, the so-called Thouless energy,
above which random matrix theory no longer applies. We determine the dependence
of the Thouless energy on the simulation parameters using the scalar
susceptibility and the number variance.Comment: LATTICE98(confine), 9 pages, 11 figure
Serum albumin and mortality risk in a hyperendemic area of HCV infection in Japan
<p>Abstract</p> <p>Background</p> <p>Hypoalbuminemia has been shown to be associated with increased mortality. We reported a mass screening in 1990 of X town in Japan, which demonstrated a high prevalence of hepatitis C virus (HCV) infection. This follow-up study determined, through a period of 12 years, whether serum albumin levels impact on the life prognosis of the residents of X town.</p> <p>Results</p> <p>Of the 509 subjects, 69 had died and 55 had moved to other regions by 2002. Therefore, we analyzed 454 people for whom we could confirm life and death between 1990 and 2002. Albumin levels were assigned to two groups, low (<4.0 g/L, group A) and normal (â„4.0 g/L, group B). Of the 454 subjects analyzed, 25 were in group A and 429 in group B and the mortality was 68.0% (17/25 cases, P < 0.00001 vs. group B) and 12.1% (52/429), respectively. Mortality from hepatocellular carcinoma (HCC) was 66.7% in group A (6/9 cases, P = 0.01 vs. group B) and 15.8% (3/19) in group B. According to multivariate analysis, five factors - 50 years or older, low albumin level (<4.0 g/L), abnormal AST level, history of smoking, and absence of alcohol consumption - were associated with death. The adjusted odds ratios for these five factors were 20.65, 10.79, 2.58, 2.24 and 2.08, respectively, and each was statistically significant.</p> <p>Conclusions</p> <p>We show that the serum albumin level is an independent risk factor for mortality from all causes in the residents of X town and an important prognostic indicator. Improvement of hypoalbuminaemia should be considered for improvement of prognosis.</p
The supersymmetric technique for random-matrix ensembles with zero eigenvalues
The supersymmetric technique is applied to computing the average spectral
density near zero energy in the large-N limit of the random-matrix ensembles
with zero eigenvalues: B, DIII-odd, and the chiral ensembles (classes AIII,
BDI, and CII). The supersymmetric calculations reproduce the existing results
obtained by other methods. The effect of zero eigenvalues may be interpreted as
reducing the symmetry of the zero-energy supersymmetric action by breaking a
certain abelian symmetry.Comment: 22 pages, introduction modified, one reference adde
Microscopic universality with dynamical fermions
It has recently been demonstrated in quenched lattice simulations that the
distribution of the low-lying eigenvalues of the QCD Dirac operator is
universal and described by random-matrix theory. We present first evidence that
this universality continues to hold in the presence of dynamical quarks. Data
from a lattice simulation with gauge group SU(2) and dynamical staggered
fermions are compared to the predictions of the chiral symplectic ensemble of
random-matrix theory with massive dynamical quarks. Good agreement is found in
this exploratory study. We also discuss implications of our results.Comment: 5 pages, 3 figures, minor modifications, to appear in Phys. Rev. D
(Rapid Commun.
Random matrix theory and symmetric spaces
In this review we discuss the relationship between random matrix theories and
symmetric spaces. We show that the integration manifolds of random matrix
theories, the eigenvalue distribution, and the Dyson and boundary indices
characterizing the ensembles are in strict correspondence with symmetric spaces
and the intrinsic characteristics of their restricted root lattices. Several
important results can be obtained from this identification. In particular the
Cartan classification of triplets of symmetric spaces with positive, zero and
negative curvature gives rise to a new classification of random matrix
ensembles. The review is organized into two main parts. In Part I the theory of
symmetric spaces is reviewed with particular emphasis on the ideas relevant for
appreciating the correspondence with random matrix theories. In Part II we
discuss various applications of symmetric spaces to random matrix theories and
in particular the new classification of disordered systems derived from the
classification of symmetric spaces. We also review how the mapping from
integrable Calogero--Sutherland models to symmetric spaces can be used in the
theory of random matrices, with particular consequences for quantum transport
problems. We conclude indicating some interesting new directions of research
based on these identifications.Comment: 161 pages, LaTeX, no figures. Revised version with major additions in
the second part of the review. Version accepted for publication on Physics
Report
Statistical analysis and the equivalent of a Thouless energy in lattice QCD Dirac spectra
Random Matrix Theory (RMT) is a powerful statistical tool to model spectral
fluctuations. This approach has also found fruitful application in Quantum
Chromodynamics (QCD). Importantly, RMT provides very efficient means to
separate different scales in the spectral fluctuations. We try to identify the
equivalent of a Thouless energy in complete spectra of the QCD Dirac operator
for staggered fermions from SU(2) lattice gauge theory for different lattice
size and gauge couplings. In disordered systems, the Thouless energy sets the
universal scale for which RMT applies. This relates to recent theoretical
studies which suggest a strong analogy between QCD and disordered systems. The
wealth of data allows us to analyze several statistical measures in the bulk of
the spectrum with high quality. We find deviations which allows us to give an
estimate for this universal scale. Other deviations than these are seen whose
possible origin is discussed. Moreover, we work out higher order correlators as
well, in particular three--point correlation functions.Comment: 24 pages, 24 figures, all included except one figure, missing eps
file available at http://pluto.mpi-hd.mpg.de/~wilke/diff3.eps.gz, revised
version, to appear in PRD, minor modifications and corrected typos, Fig.4
revise
Low-lying Eigenvalues of the QCD Dirac Operator at Finite Temperature
We compute the low-lying spectrum of the staggered Dirac operator above and
below the finite temperature phase transition in both quenched QCD and in
dynamical four flavor QCD. In both cases we find, in the high temperature
phase, a density with close to square root behavior, . In the quenched simulations we find, in addition, a
volume independent tail of small eigenvalues extending down to zero. In the
dynamical simulations we also find a tail, decreasing with decreasing mass, at
the small end of the spectrum. However, the tail falls off quite quickly and
does not seem to extend to zero at these couplings. We find that the
distribution of the smallest Dirac operator eigenvalues provides an efficient
observable for an accurate determination of the location of the chiral phase
transition, as first suggested by Jackson and Verbaarschot.Comment: LaTeX, 20 pages, 13 postscript figures. Reference added. To appear in
Nucl. Phys.
Randomness on the Lattice
In this lecture we review recent lattice QCD studies of the statistical
properties of the eigenvalues of the QCD Dirac operator. We find that the
fluctuations of the smallest Dirac eigenvalues are described by chiral Random
Matrix Theories with the global symmetries of the QCD partition function.
Deviations from chiral Random Matrix Theory beyond the Thouless energy can be
understood analytically by means of partially quenched chiral perturbation
theory.Comment: Invited talk at the International Light-Cone Meeting on
Non-Perturbative QCD and Hadron Phenomenology, Heidelberg 12-17 June 2000. 12
pages, 7 figures, Late
Gas accretion as the origin of chemical abundance gradients in distant galaxies
It has recently been suggested that galaxies in the early Universe can grow
through the accretion of cold gas, and that this may have been the main driver
of star formation and stellar mass growth. Because the cold gas is essentially
primordial, it has a very low abundance of elements heavier than helium
(metallicity). As it is funneled to the centre of a galaxy, it will lead the
central gas having an overall lower metallicity than gas further from the
centre, because the gas further out has been enriched by supernovae and stellar
winds, and not diluted by the primordial gas. Here we report chemical
abundances across three rotationally-supported star-forming galaxies at z~3,
only 2 Gyr after the Big Bang. We find an 'inverse' gradient, with the central,
star forming regions having a lower metallicity than less active ones, opposite
to what is seen in local galaxies. We conclude that the central gas has been
diluted by the accretion of primordial gas, as predicted by 'cold flow' models.Comment: To Appear in Nature Oct 14, 2010; Supplementary Information included
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