140 research outputs found
The Three Loop Equation of State of QED at High Temperature
We present the three loop contribution (order ) to the pressure of
massless quantum electrodynamics at nonzero temperature. The calculation is
performed within the imaginary time formalism. Dimensional regularization is
used to handle the usual, intermediate stage, ultraviolet and infrared
singularities, and also to prevent overcounting of diagrams during resummation.Comment: ANL-HEP-PR-94-02, SPhT/94-054 (revised final version
The Equation of State for Dense QCD and Quark Stars
We calculate the equation of state for degenerate quark matter to leading
order in hard-dense-loop (HDL) perturbation theory. We solve the
Tolman-Oppenheimer-Volkov equations to obtain the mass-radius relation for
dense quark stars. Both the perturbative QCD and the HDL equations of state
have a large variation with respect to the renormalization scale for quark
chemical potential below 1 GeV which leads to large theoretical uncertainties
in the quark star mass-radius relation.Comment: 7 pages, 3 figure
Solution to the 3-loop -derivable Approximation for Scalar Thermodynamics
We solve the 3-loop -derivable approximation to the thermodynamics of
the massless field theory by reducing it to a 1-parameter variational
problem. The thermodynamic potential is expanded in powers of and ,
where is the coupling constant, is a variational mass parameter, and
is the temperature. There are ultraviolet divergences beginning at 6th
order in that cannot be removed by renormalization. However the finite
thermodynamic potential obtained by truncating after terms of 5th order in
and defines a stable approximation to the thermodynamic functions.Comment: 4 pages, 1 figur
Restricting quark matter models by gravitational wave observation
We consider the possibilities for obtaining information about the equation of
state for quark matter by using future direct observational data on
gravitational waves. We study the nonradial oscillations of both fluid and
spacetime modes of pure quark stars. If we observe the and the lowest
modes from quark stars, by using the simultaneously obtained
radiation radius we can constrain the bag constant with reasonable
accuracy, independently of the quark mass.Comment: To appear in Phys. Rev.
Small, Dense Quark Stars from Perturbative QCD
As a model for nonideal behavior in the equation of state of QCD at high
density, we consider cold quark matter in perturbation theory. To second order
in the strong coupling constant, , the results depend sensitively on
the choice of the renormalization mass scale. Certain choices of this scale
correspond to a strongly first order chiral transition, and generate quark
stars with maximum masses and radii approximately half that of ordinary neutron
stars. At the center of these stars, quarks are essentially massless.Comment: ReVTeX, 5 pages, 3 figure
Cationic agent contrast-enhanced computed tomography imaging of cartilage correlates with the compressive modulus and coefficient of friction
SummaryObjectiveThe aim of this study is to evaluate whether contrast-enhanced computed tomography (CECT) attenuation, using a cationic contrast agent (CA4+), correlates with the equilibrium compressive modulus (E) and coefficient of friction (Ό) of ex vivo bovine articular cartilage.MethodsCorrelations between CECT attenuation and E (Group 1, n = 12) and Ό (Group 2, n = 10) were determined using 7 mm diameter bovine osteochondral plugs from the stifle joints of six freshly slaughtered, skeletally mature cows. The equilibrium compressive modulus was measured using a four-step, unconfined, compressive stress-relaxation test, and the coefficients of friction were determined from a torsional friction test. Following mechanical testing, samples were immersed in CA4+, imaged using ΌCT, rinsed, and analyzed for glycosaminoglycan (GAG) content using the 1,9-dimethylmethylene blue (DMMB) assay.ResultsThe CECT attenuation was positively correlated with the GAG content of bovine cartilage (R2 = 0.87, P < 0.0001 for Group 1 and R2 = 0.74, P = 0.001 for Group 2). Strong and significant positive correlations were observed between E and GAG content (R2 = 0.90, P < 0.0001) as well as CECT attenuation and E (R2 = 0.90, P < 0.0001). The CECT attenuation was negatively correlated with the three coefficients of friction: CECT vs Όstatic (R2 = 0.71, P = 0.002), CECT vs Όstatic_equilibrium (R2 = 0.79, P < 0.001), and CECT vs Όkinetic (R2 = 0.69, P = 0.003).ConclusionsCECT with CA4+ is a useful tool for determining the mechanical properties of ex vivo cartilage tissue as the attenuation significantly correlates with the compressive modulus and coefficient of friction
Supercharges, Killing Spinors and Intersecting Gauge Five-branes
We obtain new solutions where a string and a pp-wave lie in the common
worldvolume directions of the non-standard intersection of two gauge 5-branes
in the heterotic string. The two 5-branes are supported by independent SU(2)
Yang-Mills instantons in their respective (non-overlapping) transverse spaces.
We present a detailed study of the unbroken supersymmetry, focusing especially
on a comparison between a direct construction of Killing spinors and a counting
of zero eigenvalues in the annticommutator of supercharges. The results are in
agreement with some previous arguments, to the effect that additional zero
eigenvalues resulting from a ``fine-tuning'' between positive-energy and
negative-energy contributions from different components in an intersection are
spurious, and should not be taken as an indication of supersymmetry
enhancements. These observations have a general applicability that goes beyond
the specific example we study in this paper.Comment: Latex, 23 pages; minor revisions, and references adde
Hard Dense Loops in a Cold Non-Abelian Plasma
Classical transport theory is used to study the response of a non-Abelian
plasma at zero temperature and high chemical potential to weak color
electromagnetic fields. In this article the parallelism between the transport
phenomena occurring in a non-Abelian plasma at high temperature and high
density is stressed. Particularly, it is shown that at high densities it is
also possible to relate the transport equations to the zero-curvature condition
of a Chern-Simons theory in three dimensions, even when quarks are not
considered ultrarelativistic. The induced color current in the cold plasma can
be expressed as an average over angles, which represent the directions of the
velocity vectors of quarks having Fermi energy. From this color current it is
possible to compute -point gluonic amplitudes, with arbitrary . It is
argued that these amplitudes are the same as the ones computed in the high
chemical potential limit of QCD, that are then called hard dense loops. The
agreement between the two different formalisms is checked by computing the
polarization tensor of QED due to finite density effects in the high density
limit.Comment: 16 pages, Revtex, final version to appear in Phys. Rev. D with minor
correction
Renormalization Group Analysis of \rho-Meson Properties at Finite Density
We calculate the density dependence of the -meson mass and coupling
constant() for -nucleon-nucleon vertex at one loop using the
lagrangian where the -meson is included as a dynamical gauge boson of a
hidden local symmetry. From the condition that thermodynamic potential should
not depend on the arbitrary energy scale, renormalization scale, one can
construct a renormalization group equation for the thermodynamic potential and
argue that the various renormalization group coefficients are functions of the
density or temperature. We calculate the -function for
-nucleon-nucleon coupling constant () and -function
for -meson mass (). We found that the -meson mass
and the coupling constant for drop as density increases in the
low energy limit.Comment: 24 pages, 10 figures, revised versio
Quark number susceptibilities of hot QCD up to g^6ln(g)
The pressure of hot QCD has recently been determined to the last
perturbatively computable order g^6 ln(g) by Kajantie et al. using
three-dimensional effective theories. A similar method is applied here to the
pressure in the presence of small but non-vanishing quark chemical potentials,
and the result is used to derive the quark number susceptibilities in the limit
mu = 0. The diagonal quark number susceptibility of QCD with n_f flavours of
massless quarks is evaluated to order g^6ln(g) and compared with recent lattice
simulations. It is observed that the results qualitatively resemble the lattice
ones, and that when combined with the fully perturbative but yet undetermined
g^6 term they may well explain the behaviour of the lattice data for a wide
range of temperatures.Comment: 11 pages, 3 figures Typos corrected, references added, figures
modifie
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