917 research outputs found
The QCD equation of state for two flavours at non-zero chemical potential
We present results of a simulation of 2 flavour QCD on a
lattice using p4-improved staggered fermions with bare quark mass .
Derivatives of the thermodynamic grand canonical partition function
with respect to chemical potentials for
different quark flavours are calculated up to sixth order, enabling estimates
of the pressure and the quark number density as well as the chiral condensate
and various susceptibilities as functions of via Taylor series
expansion. Results are compared to high temperature perturbation theory as well
as a hadron resonance gas model. We also analyze baryon as well as isospin
fluctuations and discuss the relation to the chiral critical point in the QCD
phase diagram. We moreover discuss the dependence of the heavy quark free
energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes
Thermodynamic limit and semi--intensive quantities
The properties of statistical ensembles with abelian charges close to the
thermodynamic limit are discussed. The finite volume corrections to the
probability distributions and particle density moments are calculated. Results
are obtained for statistical ensembles with both exact and average charge
conservation. A new class of variables (semi--intensive variables) which differ
in the thermodynamic limit depending on how charge conservation is implemented
in the system is introduced. The thermodynamic limit behavior of these
variables is calculated through the next to leading order finite volume
corrections to the corresponding probability density distributions.Comment: 11 pages, 2 figures In v2 figures are added and corresponding
editorial changes are done. Paper will be published in Journal of Physics
Domain Wall Pinning by Step-Like Thickness Change in Magnetic Thin Film
A thin-film element with a steplike thickness change has been fabricated to investigate experimentally a pinning effect of domain walls by a shape control of thin-film devices. Using a Kerr microscope, domain observation has been done to measure pinning characteristics of the element. It has been shown that 40% steplike thickness change of the film thickness can realize a wall pinning, and a pinning field of 2.53 Oe is obtained. The pinning field increases with increasing steplike thickness change ratio
Layered Higgs Phase as a Possible Field Localisation on a Brane
So far it has been found by using lattice techniques that in the anisotropic
five--dimensional Abelian Higgs model, a layered Higgs phase exists in addition
to the expected five--dimensional one. The exploration of the phase diagram has
shown that the two Higgs phases are separated by a phase transition from the
confining phase. This transition is known to be first order. In this paper we
explore the possibility of finding a second order transition point in the
critical line which separates the first order phase transition from the
crossover region. This is shown to be the case only for the four--dimensional
Higgs layered phase whilst the phase transition to the five--dimensional broken
phase remains first order. The layered phase serves as the possible realisation
of four--dimensional spacetime dynamics which is embedded in a
five--dimensional spacetime. These results are due to gauge and scalar field
localisation by confining interactions along the extra fifth direction.Comment: 1+15 pages, 12 figure
Fluctuations in the vicinity of the phase transition line for two flavor QCD
We study the susceptibilities of quark number, isospin number and electric
charge in numerical simulations of lattice QCD at high temperature and density.
We discuss the equation of state for 2 flavor QCD at non-zero temperature and
density. Derivatives of with respect to quark chemical potential
are calculated up to sixth order. From this Taylor series, the
susceptibilities are estimated as functions of temperature and .
Moreover, we comment on the hadron resonance gas model, which explains well our
simulation results below .Comment: 3 pages, 5 figures, Talk presented at Lattice2004(non-zero
Equation of state in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach
We study the equation of state in 2+1 flavor QCD with nonperturbatively
improved Wilson quarks coupled with the RG-improved Iwasaki glue. We apply the
-integration method to nonperturbatively calculate the equation of state by
the fixed-scale approach. With the fixed-scale approach, we can purely vary the
temperature on a line of constant physics without changing the system size and
renormalization constants. Unlike the conventional fixed- approach, it is
easy to keep scaling violations small at low temperature in the fixed scale
approach. We study 2+1 flavor QCD at light quark mass corresponding to
, while the strange quark mass is chosen around the
physical point. Although the light quark masses are heavier than the physical
values yet, our equation of state is roughly consistent with recent results
with highly improved staggered quarks at large .Comment: 14 pages, 12 figures, v2: Table I and Figure 3 are corrected,
reference updated. Main discussions and conclusions are unchanged, v3:
version to appear in PRD, v4: reference adde
Critical Level Interaction of a Gravity Wave With Background Winds Driven By a Large-scale Wave Perturbation
As part of the Maui-Mesosphere and Lower Thermosphere program, data from the Utah State University Mesospheric Temperature Mapper (MTM) and the University of Illinois Meteor Wind Radar (MWR) have been used to investigate wave-driven dynamical interactions in the upper mesosphere at low latitudes. On 29 June 2003, short-period (20 min) gravity waves (GWs) were imaged in the MTM in the near-infrared OH and O2 airglow emissions for most of the night from 0700 to 1500 UT. The GWs were observed to disappear rapidly in the O2 data (peak altitude: 94 km) around 1400 UT but remained evident in the lower altitudes OH data (87 km) for a further 30 min. Coincident background wind variations measured by the MWR suggest that the GW disappearance at the O2 layer was most probably caused by a critical level (CL) interaction. However, at the OH layer, the GW fading may also have been due to wave saturation and instabilities. During this period (14001500 UT), no significant change in OH and O2 rotational temperatures were measured by the MTM; however, the background winds centered on the airglow layers were observed to increase by 10 m/s. The background wind acceleration from the disappearing gravity waves estimated from the airglow observations was larger below the CL than at the CL, consistent with the wind variation observed by the MWR
Review of Results from the NA49 Collaboration
New results of the NA49 collaboration on strange particle production are
presented. Rapidity and transverse mass spectra as well as total multiplicities
are discussed. The study of their evolution from AGS over SPS to the highest
RHIC energy reveals a couple of interesting features. These include a sudden
change in the energy dependence of the mt-spectra and of the yields of strange
hadrons around 30 AGeV. Both are found to be difficult to be reproduced in a
hadronic scenario, but might be an indication for a phase transition to a quark
gluon plasma.Comment: 8 pages, 7 figures. Proceedings of the SQM04 conference, Capetow
- …