150 research outputs found
Single-particle spectral function for the classical one-component plasma
The spectral function for an electron one-component plasma is calculated
self-consistently using the GW0 approximation for the single-particle
self-energy. In this way, correlation effects which go beyond the mean-field
description of the plasma are contained, i.e. the collisional damping of
single-particle states, the dynamical screening of the interaction and the
appearance of collective plasma modes. Secondly, a novel non-perturbative
analytic solution for the on-shell GW0 self-energy as a function of momentum is
presented. It reproduces the numerical data for the spectral function with a
relative error of less than 10% in the regime where the Debye screening
parameter is smaller than the inverse Bohr radius, kappa<1/a_B. In the limit of
low density, the non-perturbative self-energy behaves as n^(1/4), whereas a
perturbation expansion leads to the unphysical result of a density independent
self-energy [W. Fennel and H. P. Wilfer, Ann. Phys. Lpz._32_, 265 (1974)]. The
derived expression will greatly facilitate the calculation of observables in
correlated plasmas (transport properties, equation of state) that need the
spectral function as an input quantity. This is demonstrated for the shift of
the chemical potential, which is computed from the analytical formulae and
compared to the GW0-result. At a plasma temperature of 100 eV and densities
below 10^21 cm^-3, both approaches deviate less than 10% from each other.Comment: 14 pages, 9 figures accepted for publication in Phys. Rev. E v2:
added section V (application of presented formalism to chemical potential of
the OCP
Frontiers of the physics of dense plasmas and planetary interiors: experiments, theory, applications
Recent developments of dynamic x-ray characterization experiments of dense
matter are reviewed, with particular emphasis on conditions relevant to
interiors of terrestrial and gas giant planets. These studies include
characterization of compressed states of matter in light elements by x-ray
scattering and imaging of shocked iron by radiography. Several applications of
this work are examined. These include the structure of massive "Super Earth"
terrestrial planets around other stars, the 40 known extrasolar gas giants with
measured masses and radii, and Jupiter itself, which serves as the benchmark
for giant planets.Comment: Accepted to Physics of Plasmas special issue. Review from
HEDP/HEDLA-08, April 12-15, 200
Nucleon electromagnetic form factors
Elastic electromagnetic nucleon form factors have long provided vital
information about the structure and composition of these most basic elements of
nuclear physics. The form factors are a measurable and physical manifestation
of the nature of the nucleons' constituents and the dynamics that binds them
together. Accurate form factor data obtained in recent years using modern
experimental facilities has spurred a significant reevaluation of the nucleon
and pictures of its structure; e.g., the role of quark orbital angular
momentum, the scale at which perturbative QCD effects should become evident,
the strangeness content, and meson-cloud effects. We provide a succinct survey
of the experimental studies and theoretical interpretation of nucleon
electromagnetic form factors.Comment: Topical review invited by Journal of Physics G: Nuclear and Particle
Physics; 34 pages (contents listed on page 34), 11 figure
Diquarks: condensation without bound states
We employ a bispinor gap equation to study superfluidity at nonzero chemical
potential: mu .neq. 0, in two- and three-colour QCD. The two-colour theory,
QC2D, is an excellent exemplar: the order of truncation of the quark-quark
scattering kernel: K, has no qualitative impact, which allows a straightforward
elucidation of the effects of mu when the coupling is strong. In rainbow-ladder
truncation, diquark bound states appear in the spectrum of the three-colour
theory, a defect that is eliminated by an improvement of K. The corrected gap
equation describes a superfluid phase that is semi-quantitatively similar to
that obtained using the rainbow truncation. A model study suggests that the
width of the superfluid gap and the transition point in QC2D provide reliable
quantitative estimates of those quantities in QCD.Comment: 7 pages, 3 figures, REVTEX, epsfi
Quark-gluon vertex in general kinematics
The original publication can be found at www.springerlink.com Submitted to Cornell Universityâs online archive www.arXiv.org in 2007 by Jon-Ivar Skullerud. Post-print sourced from www.arxiv.org.We compute the quarkâgluon vertex in quenched lattice QCD in the Landau gauge, using an off-shell mean-field O(a)-improved fermion action. The Dirac-vector part of the vertex is computed for arbitrary kinematics. We find a substantial infrared enhancement of the interaction strength regardless of the kinematics.Ayse Kizilersu, Derek B. Leinweber, Jon-Ivar Skullerud and Anthony G. William
Sigma Terms of Light-Quark Hadrons
A calculation of the current-quark mass dependence of hadron masses can help
in using observational data to place constraints on the variation of nature's
fundamental parameters. A hadron's sigma-term is a measure of this dependence.
The connection between a hadron's sigma-term and the Feynman-Hellmann theorem
is illustrated with an explicit calculation for the pion using a rainbow-ladder
truncation of the Dyson-Schwinger equations: in the vicinity of the chiral
limit sigma_pi = m_pi/2. This truncation also provides a decent estimate of
sigma_rho because the two dominant self-energy corrections to the rho-meson's
mass largely cancel in their contribution to sigma_rho. The truncation is less
accurate for the omega, however, because there is little to compete with an
omega->rho+pi self-energy contribution that magnifies the value of sigma_omega
by ~25%. A Poincare' covariant Faddeev equation, which describes baryons as
composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain
the current-quark mass dependence of the masses of the nucleon and Delta, and
thereby sigma_N and sigma_Delta. This "quark-core" piece is augmented by the
"pion cloud" contribution, which is positive. The analysis yields sigma_N~60MeV
and sigma_Delta~50MeV.Comment: 22 pages, reference list expande
Bethe-Salpeter equation and a nonperturbative quark-gluon vertex
A Ward-Takahashi identity preserving Bethe-Salpeter kernel can always be
calculated explicitly from a dressed-quark-gluon vertex whose diagrammatic
content is enumerable. We illustrate that fact using a vertex obtained via the
complete resummation of dressed-gluon ladders. While this vertex is planar, the
vertex-consistent kernel is nonplanar and that is true for any dressed vertex.
In an exemplifying model the rainbow-ladder truncation of the gap and
Bethe-Salpeter equations yields many results; e.g., pi- and rho-meson masses,
that are changed little by including higher-order corrections. Repulsion
generated by nonplanar diagrams in the vertex-consistent Bethe-Salpeter kernel
for quark-quark scattering is sufficient to guarantee that diquark bound states
do not exist.Comment: 16 pages, 12 figures, REVTEX
Masses of ground and excited-state hadrons
We present the first Dyson-Schwinger equation calculation of the light hadron
spectrum that simultaneously correlates the masses of meson and baryon ground-
and excited-states within a single framework. At the core of our analysis is a
symmetry-preserving treatment of a vector-vector contact interaction. In
comparison with relevant quantities the
root-mean-square-relative-error/degree-of freedom is 13%. Notable amongst our
results is agreement between the computed baryon masses and the bare masses
employed in modern dynamical coupled-channels models of pion-nucleon reactions.
Our analysis provides insight into numerous aspects of baryon structure; e.g.,
relationships between the nucleon and Delta masses and those of the
dressed-quark and diquark correlations they contain.Comment: 25 pages, 7 figures, 4 table
Self-consistent Spectral Function for Non-Degenerate Coulomb Systems and Analytic Scaling Behaviour
Novel results for the self-consistent single-particle spectral function and
self-energy are presented for non-degenerate one-component Coulomb systems at
various densities and temperatures. The GW^0-method for the dynamical
self-energy is used to include many-particle correlations beyond the
quasi-particle approximation. The self-energy is analysed over a broad range of
densities and temperatures (n=10^17/cm^3-10^27/cm^3, T=10^2 eV/k_B-10^4
eV/k_B). The spectral function shows a systematic behaviour, which is
determined by collective plasma modes at small wavenumbers and converges
towards a quasi-particle resonance at higher wavenumbers. In the low density
limit, the numerical results comply with an analytic scaling law that is
presented for the first time. It predicts a power-law behaviour of the
imaginary part of the self-energy, Im Sigma ~ -n^(1/4). This resolves a long
time problem of the quasi-particle approximation which yields a finite
self-energy at vanishing density.Comment: 28 pages, 9 figure
Current quark mass effects on chiral phase transition of QCD in the improved ladder approximation
Current quark mass effects on the chiral phase transition of QCD is studied
in the improved ladder approximation. An infrared behavior of the gluon
propagator is modified in terms of an effective running coupling. The analysis
is based on a composite operator formalism and a variational approach. We use
the Schwinger-Dyson equation to give a ``normalization condition'' for the
Cornwall-Jackiw-Tomboulis effective potential and to isolate the ultraviolet
divergence which appears in an expression for the quark-antiquark condensate.
We study the current quark mass effects on the order parameter at zero
temperature and density. We then calculate the effective potential at finite
temperature and density and investigate the current quark mass effects on the
chiral phase transition. We find a smooth crossover for , and a
first-order phase transition for , T=0. Critical exponents are also
studied and our model gives the classical mean-field values. We also study the
temperature dependence of masses of scalar and pseudoscalar bosons. A critical
end point in the - plane is found at MeV,
MeV.Comment: 19 pages, 13 figure
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