140 research outputs found

    The Three Loop Equation of State of QED at High Temperature

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    We present the three loop contribution (order e4e^4) 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

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    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 Ί\Phi-derivable Approximation for Scalar Thermodynamics

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    We solve the 3-loop Ί\Phi-derivable approximation to the thermodynamics of the massless ϕ4\phi^4 field theory by reducing it to a 1-parameter variational problem. The thermodynamic potential is expanded in powers of g2g^2 and m/Tm/T, where gg is the coupling constant, mm is a variational mass parameter, and TT is the temperature. There are ultraviolet divergences beginning at 6th order in gg that cannot be removed by renormalization. However the finite thermodynamic potential obtained by truncating after terms of 5th order in gg and m/Tm/T defines a stable approximation to the thermodynamic functions.Comment: 4 pages, 1 figur

    Restricting quark matter models by gravitational wave observation

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    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 ff and the lowest wIIw_{\rm II} modes from quark stars, by using the simultaneously obtained radiation radius we can constrain the bag constant BB with reasonable accuracy, independently of the ss quark mass.Comment: To appear in Phys. Rev.

    Small, Dense Quark Stars from Perturbative QCD

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    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, αs\alpha_s, 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

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    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

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    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

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    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 nn-point gluonic amplitudes, with arbitrary nn. 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

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    We calculate the density dependence of the ρ\rho-meson mass and coupling constant(gρNNg_{\rho NN}) for ρ\rho-nucleon-nucleon vertex at one loop using the lagrangian where the ρ\rho-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 ÎČ\beta-function for ρ\rho-nucleon-nucleon coupling constant (gρNNg_{\rho NN}) and Îł\gamma-function for ρ\rho-meson mass (Îłmρ\gamma_{m_\rho}). We found that the ρ\rho-meson mass and the coupling constant for gρNNg_{\rho NN} 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)

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    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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