4,078 research outputs found
QCD phase diagram and charge fluctuations
We discuss the phase structure and fluctuations of conserved charges in two
flavor QCD. The importance of the density fluctuations to probe the existence
of the critical end point is summarized. The role of these fluctuations to
identify the first order phase transition in the presence of spinodal phase
separation is also discussed.Comment: 8 pages, 8 figures, plenary talk given at the 19th International
Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2006
(QM 2006), Shanghai, China, 14-20 Nov 200
Petrov types of slowly rotating fluid balls
Circularly rotating axisymmetric perfect fluid space-times are investigated
to second order in the small angular velocity. The conditions of various
special Petrov types are solved in a comoving tetrad formalism. A number of
theorems are stated on the possible Petrov types of various fluid models. It is
shown that Petrov type II solutions must reduce to the de Sitter spacetime in
the static limit. Two space-times with a physically satisfactory
energy-momentum tensor are investigated in detail. For the rotating
incompressible fluid, it is proven that the Petrov type cannot be D. The
equation of the rotation function can be solved for the Tolman type
IV fluid in terms of quadratures. It is also shown that the rotating version of
the Tolman IV space-time cannot be Petrov type D.Comment: 14 pages, version to appear in Gen. Rel. Gra
Quark and Nuclear Matter in the Linear Chiral Meson Model
We present an analytical description of the phase transitions from a nucleon
gas to nuclear matter and from nuclear matter to quark matter within the same
model. The equation of state for quark and nuclear matter is encoded in the
effective potential of a linear sigma model. We exploit an exact differential
equation for its dependence upon the chemical potential associated to
conserved baryon number. An approximate solution for vanishing temperature is
used to discuss possible phase transitions as the baryon density increases. For
a nucleon gas and nuclear matter we find a substantial density enhancement as
compared to quark models which neglect the confinement to baryons. The results
point out that the latter models are not suitable to discuss the phase diagram
at low temperature.Comment: 27 pages, Int.J.Mod.Phys.A versio
EoS of finite density QCD with Wilson fermions by Multi-Parameter Reweighting and Taylor expansion
The equation of state (EoS), quark number density and susceptibility at
nonzero quark chemical potential are studied in lattice QCD simulations
with a clover-improved Wilson fermion of 2-flavors and RG-improved gauge
action. To access nonzero , we employ two methods : a multi-parameter
reweighting (MPR) in and and Taylor expansion in . The use
of a reduction formula for the Wilson fermion determinant enables to study the
reweighting factor in MPR explicitly and heigher-order coefficients in Taylor
expansion free from errors of noise method, although calculations are limited
to small lattice size. As a consequence, we can study the reliability of the
thermodynamical quantities through the consistency of the two methods, each of
which has different origin of the application limit.
The thermodynamical quantities are obtained from simulations on a lattice with an intermediate quark mass(. The MPR
and Taylor expansion are consistent for the EoS and number density up to
and for the number susceptibility up to . This
implies within a given statistics that the overlap problem for the MPR and
truncation error for the Taylor expansion method are negligible in these
regions.
In order to make MPR methods work, the fluctuation of the reweighting factor
should be small. We derive the equation of the reweighting line where the
fluctuation is small, and show that the equation of the reweighting line is
consistent with the fluctuation minimum condition.Comment: 20 pages, 11 figures. Accepted to JHEP. Discussions are added.
Figures for Taylor coefficients (Fig. 7) are modifie
An effective chiral Hadron-Quark Equation of State
We construct an effective model for the QCD equation of state, taking into
account chiral symmetry restoration as well as the deconfinement phase
transition. The correct asymptotic degrees of freedom at the high and low
temperature limits are included (quarks hadrons). The model
shows a rapid crossover for both order parameters, as is expected from lattice
calculations. We then compare the thermodynamic properties of the model at
which turn out to be in qualitative agreement with lattice data,
while apparent quantitative differences can be attributed to hadronic
contributions and excluded volume corrections. Furthermore we discuss the
effects of a repulsive vector type quark interaction at finite baryon number
densities on the resulting phase diagram of the model. Our current model is
able to reproduce a first-order liquid gas phase transition as expected, but
does not show any signs of a first order deconfinement or chiral phase
transition. Both transitions rather appear as a very wide crossover in which
heavily medium modified hadron coexist with free quarks.Comment: 19 pages, 13 figures Version accepted by J. Phys.
The QCD phase diagram from analytic continuation
We present the crossover line between the quark gluon plasma and the hadron
gas phases for small real chemical potentials. First we determine the effect of
imaginary values of the chemical potential on the transition temperature using
lattice QCD simulations. Then we use various formulas to perform an analytic
continuation to real values of the baryo-chemical potential. Our data set
maintains strangeness neutrality to match the conditions of heavy ion physics.
The systematic errors are under control up to MeV. For the
curvature of the transition line we find that there is an approximate agreement
between values from three different observables: the chiral susceptibility,
chiral condensate and strange quark susceptibility. The continuum extrapolation
is based on 10, 12 and 16 lattices. By combining the analysis for these
three observables we find, for the curvature, the value .Comment: 14 pages, 4 figures, revised versio
Technicolor and Beyond: Unification in Theory Space
The salient features of models of dynamical electroweak symmetry breaking are
reviewed. The ideal walking idea is introduced according to which one should
carefully take into account the effects of the extended technicolor dynamics on
the technicolor dynamics itself. The effects amount at the enhancement of the
anomalous dimension of the mass of the techniquarks allowing to decouple the
Flavor Changing Neutral Currents problem from the one of the generation of the
top mass. Precision data constraints are reviewed focussing on the latest
crucial observation that the S-parameter can be computed exactly near the upper
end of the conformal window (Conformal S-parameter) with relevant consequences
on the selection of nature's next strong force. We will then introduce the
Minimal Walking Technicolor (MWT) models. In the second part of this review we
consider the interesting possibility to marry supersymmetry and technicolor.
The reason is to provide a unification of different extensions of the standard
model. For example, this means that one can recover, according to the
parameters and spectrum of the theory distinct extensions of the standard
model, from supersymmetry to technicolor and unparticle physiscs. A surprising
result is that a minimal (in terms of the smallest number of fields)
supersymmetrization of the MWT model leads to the maximal supersymmetry in four
dimensions, i.e. N=4 SYM.Comment: Extended version of the PASCOS10 proceedings for the Plenary Tal
Extremely energetic cosmic neutrinos: Opportunities for astrophysics, particle physics, and cosmology
Existing and planned observatories for cosmic neutrinos open up a huge window
in energy from 10^7 to 10^17 GeV. Here, we discuss in particular the
possibilities to use extremely energetic cosmic neutrinos as a diagnostic of
astrophysical processes, as a tool for particle physics beyond the Standard
Model, and as a probe of cosmology.Comment: 10 pages, 7 figures, ws-procs9x6.cls, talk presented at the ARENA
Workshop, DESY, Zeuthen, Germany, May 17-19, 200
The QCD equation of state at finite density from analytical continuation
We determine the equation of state of QCD at finite chemical potential, to
order , for a system of 2+1 quark flavors. The simulations are
performed at the physical mass for the light and strange quarks on several
lattice spacings; the results are continuum extrapolated using lattices of up
to temporal resolution. The QCD pressure and interaction measure are
calculated along the isentropic trajectories in the plane
corresponding to the RHIC Beam Energy Scan collision energies. Their behavior
is determined through analytic continuation from imaginary chemical potentials
of the baryonic density. We also determine the Taylor expansion coefficients
around from the simulations at imaginary chemical potentials.
Strangeness neutrality and charge conservation are imposed, to match the
experimental conditions.Comment: 5 pages, 4 figure
Towards the QCD phase diagram from analytical continuation
We calculate the QCD cross-over temperature, the equation of state and
fluctuations of conserved charges at finite density by analytical continuation
from imaginary to real chemical potentials. Our calculations are based on new
continuum extrapolated lattice simulations using the 4stout staggered actions
with a lattice resolution up to . The simulation parameters are tuned
such that the strangeness neutrality is maintained, as it is in heavy ion
collisions.Comment: 4 pages, 2 figures, Proceedings of the Quark Matter 2015 conference,
Kobe, Japa
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