2,874 research outputs found
Lattice QCD at finite temperature and density
We study the phase structure of QCD at finite temperature and density by
numerical simulations on a lattice. The most important point for the numerical
study at finite density is treatment of the sign problem. We propose a method
to avoid the sign problem, which is based on a cumulant expansion of the
complex phase in the density of state method combined with the reweighting
method. Using the method, we study the critical point terminating a first order
phase transition line in lattice QCD at high temperature and density.Comment: 6 pages, 4 figures, talk presented at the YITP workshop on "New
Frontiers in QCD 2010", March 1-19, 2010, Kyoto, Japa
Solubility, Light Output and Energy Resolution Studies of Molybdenum-Loaded Liquid Scintillators
The search for neutrinoless double-beta decay is an important part of the
global neutrino physics program. One double-beta decay isotope currently under
investigation is 100Mo. In this article, we discuss the results of a
feasibility study investigating the use of molybdenum-loaded liquid
scintillator. A large, molybdenum-loaded liquid scintillator detector is one
potential design for a low-background, internal-source neutrinoless double-beta
decay search with 100Mo. The program outlined in this article included the
selection of a solute containing molybdenum, a scintillating solvent and the
evaluation of the mixture's performance as a radiation detector.Comment: 8 pages, 3 figure
Lee-Yang zero analysis for the study of QCD phase structure
We comment on the Lee-Yang zero analysis for the study of the phase structure
of QCD at high temperature and baryon number density by Monte-Carlo
simulations. We find that the sign problem for non-zero density QCD induces a
serious problem in the finite volume scaling analysis of the Lee-Yang zeros for
the investigation of the order of the phase transition. If the sign problem
occurs at large volume, the Lee-Yang zeros will always approach the real axis
of the complex parameter plane in the thermodynamic limit. This implies that a
scaling behavior which would suggest a crossover transition will not be
obtained. To clarify this problem, we discuss the Lee-Yang zero analysis for
SU(3) pure gauge theory as a simple example without the sign problem, and then
consider the case of non-zero density QCD. It is suggested that the
distribution of the Lee-Yang zeros in the complex parameter space obtained by
each simulation could be more important information for the investigation of
the critical endpoint in the plane than the finite volume scaling
behavior.Comment: 16 pages, 3 figures, 2 tables, minor change
Critical point in finite density lattice QCD by canonical approach
We propose a method to find the QCD critical point at finite density
calculating the canonical partition function by
Monte-Carlo simulations of lattice QCD, and analyze data obtained by a
simulation with two-flavor p4-improved staggered quarks with pion mass . It is found that the shape of an effective potential
changes gradually as the temperature decreases and a first order phase
transition appears in the low temperature and high density region. This result
strongly suggests the existence of the critical point in the phase
diagram.Comment: 4 pages, 2 figures, To appear in the conference proceedings for Quark
Matter 2009, March 30 - April 4, Knoxville, Tennesse
Study of the critical point in lattice QCD at high temperature and density
We propose a method to probe the nature of phase transitions in lattice QCD
at finite temperature and density, which is based on the investigation of an
effective potential as a function of the average plaquette. We analyze data
obtained in a simulation of two-flavor QCD using p4-improved staggered quarks
with bare quark mass , and find that a first order phase transition
line appears in the high density regime for . The effective
potential as a function of the quark number density is also studied. We
calculate the chemical potential as a function of the density from the
canonical partition function and discuss the existence of the first order phase
transition line.Comment: 7 pages, 7 figures, talk presented at Lattice 200
Phase structure of hot dense QCD by a histogram method
We study the phase structure of QCD at high temperature and density by
lattice QCD simulations adopting a histogram method. The quark mass dependence
and the chemical potential dependence of the nature of phase transition are
investigated focusing on the probability distribution function (histogram). The
shape of the distribution function changes with the quark mass and chemical
potential. Through the shape of the distribution, the critical surface which
separates the first order transition and crossover regions in the heavy quark
region is determined for the (2+1)-flavor case. Moreover, we determined the
critical point at finite density for two-flavor QCD with an intermediate quark
mass, using a Gaussian approximation of the complex phase distribution of the
quark determinant. The chemical potential dependence of the critical quark mass
is also evaluated in the situation where two light quarks and many massive
quarks exist. We find that the first order transition region becomes wider with
the chemical potential in the many-flavor QCD.Comment: 16 pages, 20 figures, mini-revie
Remarks on the reweighting method in the chemical potential direction
We comment on the reweighting method in the chemical potential direction. We study the fluctuation of the reweighting factor during
Monte-Carlo steps. We find that it is the absolute value of the reweighting
factor that mainly contributes to the shift of the phase transition line
by the presence of . The phase fluctuation is a cause
of the sign problem, but the effect on seems to be small. We also
discuss for Iso-vector chemical potential and determined
from simulations with imaginary chemical potential.Comment: 5pages, 2 figures, Contribution to SEWM 2002 (Heidelberg, 2-5 October
2002
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