240 research outputs found
Perturbative QCD at non-zero chemical potential: Comparison with the large-Nf limit and apparent convergence
The perturbative three-loop result for the thermodynamic potential of QCD at
finite temperature and chemical potential as obtained in the framework of
dimensional reduction is compared with the exact result in the limit of large
flavor number. The apparent convergence of the former as well as possibilities
for optimization are investigated. Corresponding optimized results for full QCD
are given for the case of two massless quark flavors.Comment: REVTEX4, 4 pages, 3 color figures. v2: fig. 3 now includes also
lattice data for two-flavor QCD at nonzero chemical potentia
Anomalous specific heat in high-density QED and QCD
Long-range quasi-static gauge-boson interactions lead to anomalous
(non-Fermi-liquid) behavior of the specific heat in the low-temperature limit
of an electron or quark gas with a leading term. We obtain
perturbative results beyond the leading log approximation and find that
dynamical screening gives rise to a low-temperature series involving also
anomalous fractional powers . We determine their coefficients in
perturbation theory up to and including order and compare with exact
numerical results obtained in the large- limit of QED and QCD.Comment: REVTEX4, 6 pages, 2 figures; v2: minor improvements, references
added; v3: factor of 2 error in the T^(7/3) coefficient corrected and plots
update
E-Selectin and markers of HIV disease severity, inflammation and coagulation in HIV-infected treatment-naïve individuals
Background: E-selectin has been shown to play a role in atherosclerosis and to be increased in HIV-infected individuals due to chronic immune activation. There is a paucity of studies on E-selectin in HIV-infected treatment-naïve individuals. Objectives: This study aimed to determine whether E-selectin levels were increased in HIV-infected treatment-naïve individuals and whether these correlated with markers of disease severity, inflammation and coagulation to determine if this population is at risk for cardiovascular disease (CVD).Methods: E-selectin levels were determined in 114 HIV-infected treatment-naive and 66 HIV-negative individuals, compared between groups and correlated with markers of disease severity, inflammation and coagulation.Results: There were statistically significant differences (p<0.01) in levels of WCC, CD4+ count, %CD38/8, albumin, IgG, hsCRP and D-dimer between groups and no statistically significant differences in E-selectin (p=0.84) and fibrinogen (p=0.65) levels. E-selectin correlated with age (p=0.02) and gender (p=0.01). Conclusion: E-selectin was a poor marker in this setting. There was no correlation with any of the markers of disease severity, inflammation and coagulation. E-selectin is most likely raised in an acute inflammatory setting, rather than chronic stage of HIV-infection. We recommend that other markers be utilized to identify patients at increased risk of CVD; as these were significantly increased untreated in individuals.Keywords: E-selectin, inflammation and coagulation in HIV-infected treatment-naïve individuals
The pressure of deconfined QCD for all temperatures and quark chemical potentials
We present a new method for the evaluation of the perturbative expansion of
the QCD pressure which is valid at all values of the temperature and quark
chemical potentials in the deconfined phase and which we work out up to and
including order g^4 accuracy. Our calculation is manifestly four-dimensional
and purely diagrammatic -- and thus independent of any effective theory
descriptions of high temperature or high density QCD. In various limits, we
recover the known results of dimensional reduction and the HDL and HTL
resummation schemes, as well as the equation of state of zero-temperature quark
matter, thereby verifying their respective validity. To demonstrate the overlap
of the various regimes, we furthermore show how the predictions of dimensional
reduction and HDL resummed perturbation theory agree in the regime
T~\sqrt{g}*mu. At parametrically smaller temperatures T~g*mu, we find that the
dimensional reduction result agrees well with those of the nonstatic
resummations down to the remarkably low value T~0.2 m_D, where m_D is the Debye
mass at T=0. Beyond this, we see that only the latter methods connect smoothly
to the T=0 result of Freedman and McLerran, to which the leading small-T
corrections are given by the so-called non-Fermi-liquid terms, first obtained
through HDL resummations. Finally, we outline the extension of our method to
the next order, where it would include terms for the low-temperature entropy
and specific heats that are unknown at present.Comment: 45 pages, 21 figures; v2: minor corrections and clarifications,
references added; v3: Fig 16 added, version accepted for publication in PR
Non-Abelian plasma instabilities: SU(3) vs. SU(2)
We present the first 3+1 dimensional simulations of non-Abelian plasma
instabilities in gauge-covariant Boltzmann-Vlasov equations for the QCD gauge
group SU(3) as well as for SU(4) and SU(5). The real-time evolution of
instabilities for a plasma with stationary momentum-space anisotropy is studied
using a hard-loop effective theory that is discretized in the velocities of
hard particles. We find that the numerically less expensive calculations using
the group SU(2) essentially reproduce the nonperturbative dynamics of
non-Abelian plasma instabilities with higher rank gauge groups provided the
mass parameters of the corresponding hard-loop effective theories are the same.
In particular we find very similar spectra for the turbulent cascade that forms
in the strong-field regime, which is associated with an approximately linear
growth of energy in collective fields. The magnitude of the linear growth
however turns out to increase with the number of colors.Comment: 8 pages, 7 figures; v2: minor changes; accepted for publication in
Phys. Rev.
A nonequilibrium renormalization group approach to turbulent reheating
We use nonequilibrium renormalization group (RG) techniques to analyze the
thermalization process in quantum field theory, and by extension reheating
after inflation. Even if at a high scale the theory is described by a
non-dissipative theory, the RG running induces nontrivial
noise and dissipation. For long wavelength, slowly varying field
configurations, the noise and dissipation are white and ohmic, respectively.
The theory will then tend to thermalize to an effective temperature given by
the fluctuation-dissipation theorem.Comment: 8 pages, 2 figures; to appear in J. Phys. A; more detailed account of
the calculation of the noise and dissipation kernel
The magnetic mass of transverse gluon, the B-meson weak decay vertex and the triality symmetry of octonion
With an assumption that in the Yang-Mills Lagrangian, a left-handed fermion
and a right-handed fermion both expressed as quaternion make an octonion which
possesses the triality symmetry, I calculate the magnetic mass of the
transverse self-dual gluon from three loop diagram, in which a heavy quark pair
is created and two self-dual gluons are interchanged.
The magnetic mass of the transverse gluon depends on the mass of the pair
created quarks, and in the case of charmed quark pair creation, the magnetic
mass becomes approximately equal to at MeV. A possible time-like magnetic gluon mass
from two self-dual gluon exchange is derived, and corrections in the B-meson
weak decay vertices from the two self-dual gluon exchange are also evaluated.Comment: 22 pages, 9 figure
Thermodynamics of Large-N_f QCD at Finite Chemical Potential
We extend the previously obtained results for the thermodynamic potential of
hot QCD in the limit of large number of fermions to non-vanishing chemical
potential. We give exact results for the thermal pressure in the entire range
of temperature and chemical potential for which the presence of a Landau pole
is negligible numerically. In addition we compute linear and non-linear quark
susceptibilities at zero chemical potential, and the entropy at small
temperatures. We compare with the available perturbative results and determine
their range of applicability. Our numerical accuracy is sufficiently high to
check and verify existing results, including the recent perturbative results by
Vuorinen on quark number susceptibilities and the older results by Freedman and
McLerran on the pressure at zero temperature and high chemical potential. We
also obtain a number of perturbative coefficients at sixth order in the
coupling that have not yet been calculated analytically. In the case of both
non-zero temperature and non-zero chemical potential, we investigate the range
of validity of a scaling behaviour noticed recently in lattice calculations by
Fodor, Katz, and Szabo at moderately large chemical potential and find that it
breaks down rather abruptly at , which points to a
presumably generic obstruction for extrapolating data from small to large
chemical potential. At sufficiently small temperatures , we find
dominating non-Fermi-liquid contributions to the interaction part of the
entropy, which exhibits strong nonlinearity in the temperature and an excess
over the free-theory value.Comment: 18 pages, 7 figures, JHEP style; v2: several updates, rewritten and
extended sect. 3.4 covering now "Entropy at small temperatures and
non-Fermi-liquid behaviour"; v3: additional remarks at the end of sect. 3.4;
v4: minor corrections and additions (version to appear in JHEP
The pressure of QCD at finite temperatures and chemical potentials
The perturbative expansion of the pressure of hot QCD is computed here to
order g^6ln(g) in the presence of finite quark chemical potentials. In this
process all two- and three-loop one-particle irreducible vacuum diagrams of the
theory are evaluated at arbitrary T and mu, and these results are then used to
analytically verify the outcome of an old order g^4 calculation of Freedman and
McLerran for the zero-temperature pressure. The results for the pressure and
the different quark number susceptibilities at high T are compared with recent
lattice simulations showing excellent agreement especially for the chemical
potential dependent part of the pressure.Comment: 35 pages, 6 figures; text revised, one figure replace
- …