748 research outputs found
A generating functional for ultrasoft amplitudes in hot QCD
The effective amplitudes for gluon momentum p<<gT in hot QCD exhibit damping
as a result of collisions. The whole set of n-point amplitudes is shown to be
generated from one functional K(x,y;A), in addition to the induced current
j(x;A).Comment: 7 pages, no figure (some comments added
Correlation functions and dissipation in hot QCD
A recently proposed generating functional allows the construction of the full
set of n-point Green functions in QCD at high temperature and at distances
larger than 1/gT. One may then learn how the system maintains its thermal
equilibrium in the quantum field theory approach, i.e. which process
compensates for the important dissipation due to collisions. This system may be
characterized by quantities which have a classical limit. One finds that the
fluctuations of the coloured field are not gaussian ones. A comparison is made
with the semi-classical approach where a random noise is the source of
fluctuations.Comment: 21 pages, latex 2e, no figure Comments added in Introduction, in Sec
Proton-nucleus collisions in the color glass condensate framework
We discuss proton-nucleus collisions in the framework of the color glass
condensate. By assuming that the proton can be described as a low density color
source, we solve exactly the Yang-Mills equations corresponding to this type of
collision, and then use this solution in order to calculate inclusive gluon
production or quark-antiquark production. Our result shows that
k_T-factorization, while valid for gluon production, is violated for quark pair
production in proton-nucleus collisions.Comment: Talk given at SEWM2004, Helsinki, June 200
Violation of kT factorization in quark production from the Color Glass Condensate
We examine the violation of the kT factorization approximation for quark
production in high energy proton-nucleus collisions. We comment on its
implications for the open charm and quarkonium production in collider
experiments.Comment: 4 pages, 6 figures, contribution to proceedings of Quark Matter 2005,
Budapest, Aug 4-
Theory of antibound states in partially filled narrow band systems
We present a theory of the dynamical two-particle response function in the
Hubbard model based on the time-dependent Gutzwiller approximation. The results
are in excellent agreement with exact diagonalization on small clusters and
give reliable results even for high densities, where the usual ladder
approximation breaks down. We apply the theory to the computation of antibound
states relevant for Auger spectroscopy and cold atom physics. A special bonus
of the theory is its computational simplicity.Comment: 4 pages, 3 figure
Triplon mean-field analysis of an antiferromagnet with degenerate Shastry-Sutherland ground states
We look into the quantum phase diagram of a spin-
antiferromagnet on the square lattice with degenerate Shastry-Sutherland ground
states, for which only a schematic phase diagram is known so far. Many exotic
phases were proposed in the schematic phase diagram by the use of exact
diagonalization on very small system sizes. In our present work, an important
extension of this antiferromagnet is introduced and investigated in the
thermodynamic limit using triplon mean-field theory. Remarkably, this
antiferromagnet shows a stable plaquette spin-gapped phase like the original
Shastry-Sutherland antiferromagnet, although both of these antiferromagnets
differ in the Hamiltonian construction and ground state degeneracy. We propose
a sublattice columnar dimer phase which is stabilized by the second and third
neighbor antiferromagnetic Heisenberg exchange interactions. There are also
some commensurate and incommensurate magnetically ordered phases, and other
spin-gapped phases which find their places in the quantum phase diagram.
Mean-field results suggest that there is always a level-crossing phase
transition between two spin gapped phases, whereas in other situations, either
a level-crossing or a continuous phase transition happens
Dust Distribution during Reionization
The dust produced by the first generation of stars will be a foreground to
cosmic microwave background. In order to evaluate the effect of this early
dust, we calculate the power spectrum of the dust emission anisotropies and
compare it with the sensitivity limit of the Planck satellite. The spatial
distribution of the dust is estimated through the distribution of dark matter.
At small angular scales () the dust signal is found to be
noticeable with the Planck detector for certain values of dust lifetime and
production rates. The dust signal is also compared to sensitivities of other
instruments. The early dust emission anisotropies are finally compared to those
of local dust and they are found to be similar in magnitude at mm wavelengths.Comment: 6 pages, 6 figures; Typos fixed. Clarifications in the abstract,
sections 2 and 4.1 and fig
Exact Calculation of Ring Diagrams and the Off-shell Effect on the Equation of State
The partition function with ring diagrams at finite temperature is exactly
caluclated by using contour integrals in the complex energy plane. It contains
a pole part with temperature and momentum dependent mass and a phase shift part
induced by off-shell effect in hot medium. The thermodynamic potentials for
and interactions are calculated and compared with the
quasi-particle (pole) approximation. It is found that the off-shell effect on
the equation of state is remarkable.Comment: 7 pages, 11 figures, refereces added, final version to appear in PR
Leakage Effect on J/psi Pt Distributions in Different Centrality Bins for Pb-Pb Collisions at E/A=160 GeV
A transport approach including a leakage effect for J/psi's in the transverse
phase space is used to calculate the ratios between the J/psi transverse
momentum distributions in several centrality bins for Pb-Pb collisions at E/A =
160 GeV. From the comparison with the CERN-SPS data, where the centrality is
characterized by the transverse energy Et, the leakage effect is extremely
important in the region of high transverse momentum and high transverse energy,
and both the threshold and the comover models can describe the ratio well for
all centrality bins except the most central one (Et < 100 GeV), for which the
comover model calculation is considerably better than the threshold one.Comment: 4 pages, 2 figures, REVTEX3.1, accepted for publication in Phys. Rev.
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