485 research outputs found
Classical Strongly Coupled QGP II: Screening and Equation of State
We analyze the screening and bulk energy of a classical and strongly
interacting plasma of color charges, a model we recently introduced for the
description of a quark-gluon plasma at T=(1-3)Tc. The partition function is
organized around the Debye-Huckel limit. The linear Debye-Huckel limit is
corrected by a virial expansion. For the pressure, the expansion is badly
convergent even in the dilute limit. The non-linear Debye-Huckel theory is
studied numerically as an alternative for moderately strong plasmas. We use
Debye theory of solid to extend the analysis to the crystal phase at very
strong coupling. The analytical results for the bulk energy per particle
compare well with the numerical results from molecular dynamics simulation for
all couplings.Comment: 9 pages, 5 figure
Reconstructing the Inflaton Potential
A review is presented of recent work by the authors concerning the use of
large scale structure and microwave background anisotropy data to determine the
potential of the inflaton field. The importance of a detection of the
stochastic gravitational wave background is emphasised, and some preliminary
new results of tests of the method on simulated data sets with uncertainties
are described. (Proceedings of ``Unified Symmetry in the Small and in the
Large'', Coral Gables, 1994)Comment: 13 pages, uuencoded postscript file with figures included (LaTeX file
available from ARL), FERMILAB-Conf 94/189
Nonthermal Supermassive Dark Matter
We discuss several cosmological production mechanisms for nonthermal
supermassive dark matter and argue that dark matter may be elementary particles
of mass much greater than the weak scale. Searches for dark matter should not
be limited to weakly interacting particles with mass of the order of the weak
scale, but should extend into the supermassive range as well.Comment: 11 page LaTeX file. No major changes. Version accepted by PR
Femtolensing and Picolensing by Axion Miniclusters
Non-linear effects in the evolution of the axion field in the early Universe
may lead to the formation of gravitationally bound clumps of axions, known as
``miniclusters.'' Minicluster masses and radii should be in the range and cm, and in plausible
early-Universe scenarios a significant fraction of the mass density of the
Universe may be in the form of axion miniclusters. If such axion miniclusters
exist, they would have the physical properties required to be detected by
``femtolensing.''Comment: 7 pages plus 2 figures (Fig.1 avalible upon request), LaTe
On cosmological observables in a swiss-cheese universe
Photon geodesics are calculated in a swiss-cheese model, where the cheese is
made of the usual Friedmann-Robertson-Walker solution and the holes are
constructed from a Lemaitre-Tolman-Bondi solution of Einstein's equations. The
observables on which we focus are the changes in the redshift, in the
angular-diameter--distance relation, in the luminosity-distance--redshift
relation, and in the corresponding distance modulus. We find that redshift
effects are suppressed when the hole is small because of a compensation effect
acting on the scale of half a hole resulting from the special case of spherical
symmetry. However, we find interesting effects in the calculation of the
angular distance: strong evolution of the inhomogeneities (as in the approach
to caustic formation) causes the photon path to deviate from that of the FRW
case. Therefore, the inhomogeneities are able to partly mimic the effects of a
dark-energy component. Our results also suggest that the nonlinear effects of
caustic formation in cold dark matter models may lead to interesting effects on
photon trajectories.Comment: 25 pages, 21 figures; replaced to fit the version accepted for
publication in Phys. Rev.
Harrison-Z'eldovich primordial spectrum is consistent with observations
Inflation predicts primordial scalar perturbations with a nearly
scale-invariant spectrum and a spectral index approximately unity (the
Harrison--Zel'dovich (HZ) spectrum). The first important step for inflationary
cosmology is to check the consistency of the HZ primordial spectrum with
current observations. Recent analyses have claimed that a HZ primordial
spectrum is excluded at more than 99% c.l.. Here we show that the HZ spectrum
is only marginally disfavored if one considers a more general reionization
scenario. Data from the Planck mission will settle the issue.Comment: 4 Pages, 2 Figure
Classical Strongly Coupled QGP I: The Model and Molecular Dynamics Simulations
We propose a model for the description of strongly interacting quarks and
gluon quasiparticles at , as a classical and nonrelativistic
colored Coulomb gas. The sign and strength of the inter-particle interactions
are fixed by the scalar product of their classical {\it color vectors} subject
to Wong's equations. The model displays a number of phases as the Coulomb
coupling is increased ranging from a gas, to a liquid, to a crystal with
antiferromagnetic-like color ordering. We analyze the model using Molecular
Dynamics (MD) simulations and discuss the density-density correlator in real
time. We extract pertinent decorrelation times, diffusion and viscosity
constants for all phases. The classical results when extrapolated to the sQGP
suggest that the phase is liquid-like, with a diffusion constant and a bulk viscosity to entropy density ratio .Comment: 11 pages, 14 figure
Light-cone averages in a swiss-cheese universe
We analyze a toy swiss-cheese cosmological model to study the averaging
problem. In our model, the cheese is the EdS model and the holes are
constructed from a LTB solution. We study the propagation of photons in the
swiss-cheese model, and find a phenomenological homogeneous model to describe
observables. Following a fitting procedure based on light-cone averages, we
find that the the expansion scalar is unaffected by the inhomogeneities. This
is because of spherical symmetry. However, the light-cone average of the
density as a function of redshift is affected by inhomogeneities. The effect
arises because, as the universe evolves, a photon spends more and more time in
the (large) voids than in the (thin) high-density structures. The
phenomenological homogeneous model describing the light-cone average of the
density is similar to the concordance model. Although the sole source in the
swiss-cheese model is matter, the phenomenological homogeneous model behaves as
if it has a dark-energy component. Finally, we study how the equation of state
of the phenomenological model depends on the size of the inhomogeneities, and
find that the equation-of-state parameters w_0 and w_a follow a power-law
dependence with a scaling exponent equal to unity. That is, the equation of
state depends linearly on the distance the photon travels through voids. We
conclude that within our toy model, the holes must have a present size of about
250 Mpc to be able to mimic the concordance model.Comment: 20 pages, 14 figures; replaced to fit the version accepted for
publication in Phys. Rev.
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