20 research outputs found
A fit of the angular 3–point function and biased galaxy formation
A study of the 3-point function, based on the analysis of momenta (as was done, e.g., in Sharp et.al. 1984) deduced from the Zwicky catalog, indicates that an expression containing a cubic term, besides the usual second degree polynomials of 2–point functions, provides a good fit of angular data
Mixed Models with n>1 and Large Scale Structure constraints
Recent data on CBR anisotropies show a Doppler peak higher than expected in
CDM cosmological models, if the spectral index . However, CDM and LCDM
models with n>1 can hardly be consistent with LSS data. Mixed models, instead,
whose transfer function is naturally steeper because of free--streaming in the
hot component, may become consistent with data if n>1, when Omega_h is large.
This is confirmed by our detailed analysis, extended both to models with a hot
component whose momentum space distribution had a thermal origin (like massive
neutrinos), and to models with a non--cold component arising from heavier
particle decay. In this work we systematically search models which fulfill all
constraints which can be implemented at the linear level. We find that a
stringent linear constraint arises from fitting the extra-power parameter
Gamma. Other significant constraints arise comparing the expected abundances of
galaxy clusters and high-z systems with observational data. Keeping to models
with Gamma \geq 0.13, a suitable part of the space parameter still allows up to
\sim 30% of hot component (it is worth outlining that our stringent criteria
allow only models with 0.10 \mincir Omega_h \mincir 0.16, if n \leq 1). We also
outline that models with such large non--cold component would ease the solution
of the so--called baryon catastrophe in galaxy clusters.Comment: 28 pages + 9 figures, uses elsart.sty, to be published in New
Astronom
EVAPORATION OF QUARK DROPS DURING THE COSMOLOGICAL Q-H TRANSITION
We have carried out a study of the hydrodynamics of disconnected quark
regions during the final stages of the cosmological quark-hadron transition. A
set of relativistic Lagrangian equations is presented for following the
evaporation of a single quark drop and results from the numerical solution of
this are discussed. A self-similar solution is shown to exist and the formation
of baryon number density inhomogeneities at the end of the drop contraction is
discussed.Comment: 12 pages Phys. Rev. format, uuencoded postscript file including 12
figure
Cosmic opacity to CMB photons and polarization measurements
Anisotropy data analysis leaves a significant degeneracy between primeval
spectral index (n_s) and cosmic opacity to CMB photons (\tau). Low--l
polarization measures, in principle, can remove it. We perform a likelihood
analysis to see how cosmic variance possibly affects such a problem. We find
that, for a sufficiently low noise level (\sigma_{pix}) and if \tau is not
negligibly low, the degeneracy is greatly reduced, while the residual impact of
cosmic variance on n_s and \tau determinations is under control. On the
contrary, if \sigma_{pix} is too high, cosmic variance effects appear to be
magnified. We apply general results to specific experiments and find that, if
favorable conditions occur, it is possible that a 2--\sigma detection of a
lower limit on \tau is provided by the SPOrt experiment. Furthermore, if the
PLANCK experiment will measure polarization with the expected precision, the
error on low--l harmonics is adequate to determine \tau, without significant
magnification of the cosmic variance. This however indicates that high
sensitivity might be more important than high resolution in \tau
determinations. We also outline that a determination of \tau is critical to
perform detailed analyses on the nature of dark energy and/or on the presence
of primeval gravitational waves.Comment: 17 pages, 11 figures, to be published on New Astronom
Do WMAP data favor neutrino mass and a coupling between Cold Dark Matter and Dark Energy?
Within the frame of cosmologies where Dark Energy (DE) is a self--interacting
scalar field, we allow for a CDM--DE coupling and non--zero neutrino masses,
simultaneously. In their 0--0 version, i.e. in the absence of coupling and
neutrino mass, these cosmologies provide an excellent fit to WMAP, SNIa and
deep galaxy sample spectra, at least as good as \LambdaCDM. When the new
degrees of freedom are open, we find that CDM--DE coupling and significant
neutrino masses (~0.1eV per \nu species) are at least as likely as the 0--0
option and, in some cases, even statistically favoured. Results are obtained by
using a Monte Carlo Markov Chain approach.Comment: 18 pages, 10 figures, submitted to JCA
Dynamical Dark Energy model parameters with or without massive neutrinos
We use WMAP5 and other cosmological data to constrain model parameters in
quintessence cosmologies, focusing also on their shift when we allow for
non-vanishing neutrino masses. The Ratra-Peebles (RP) and SUGRA potentials are
used here, as examples of slowly or fastly varying state parameter w(a). Both
potentials depend on an energy scale \Lambda. Here we confirm the results of
previous analysis with WMAP3 data on the upper limits on \Lambda, which turn
out to be rather small (down to ~10^{-9} in RP cosmologies and ~10^{-5} for
SUGRA). Our constraints on \Lambda are not heavily affected by the inclusion of
neutrino mass as a free parameter. On the contrary, when the neutrino mass
degree of freedom is opened, significant shifts in the best-fit values of other
parameters occur.Comment: 9 pages, 3 figures, submitted to JCA
Nature of Dark Energy and Polarization Measurements
High sensitivity polarization measures, on wide angular scales, together with
data on anisotropy, can be used to fix DE parameters. In this paper, first of
all, we aim to determine the sensitivity needed to provide significant limits.
Our analysis puts in evidence that there is a class of DE models that
polarization measures can possibly exclude soon. This class includes models
with DE due to a Ratra-Peebles (RP) potential. Using a likelihood analysis, we
show that it is possible to distinguish RP models from LCDM and other dynamical
DE models, already with the sensitivity of experiments like SPOrt or WMAP,
thanks to their negative TE correlation at low-l, when the optical depth tau is
sufficiently large. On the contrary, fixing the energy scale Lambda for RP
potentials or distinguishing between LCDM and other DE potentials requires a
much lower pixel noise, that no planned polarization experiment will achieve.
While reviewing this paper after the referee report, the first-year WMAP data
were released. WMAP finds large positive anisotropy-polarization correlations
at low l; this apparently excludes DE models with RP potentials.Comment: 28 pages, 16 figures, to be published in New Astronomy; replaced with
accepted versio
Primordial nuggets survival and QCD pairing
We revisit the problem of boiling and surface evaporation of quark nuggets in
the cosmological quark-hadron transition with the explicit consideration of
pairing between quarks in a color-flavor locked (CFL) state. Assuming that
primordial quark nuggets are actually formed, we analyze the consequences of
pairing on the rates of boiling and surface evaporation in order to determine
whether they could have survived with substantial mass. We find a substantial
quenching of the evaporation + boiling processes, which suggests the survival
of primordial nuggets for the currently considered range of the pairing gap
. Boiling is shown to depend on the competition of an increased
stability window and the suppression of the rate, and is not likely to dominate
the destruction of the nuggets. If surface evaporation dominates, the fate of
the nuggets depend on the features of the initial mass spectrum of the nuggets,
their evaporation rate, and the value of the pairing gap, as shown and
discussed in the text.Comment: 6 pages, 4 figure
Measuring the metric: a parametrized post-Friedmanian approach to the cosmic dark energy problem
We argue for a ``parametrized post-Friedmanian'' approach to linear
cosmology, where the history of expansion and perturbation growth is measured
without assuming that the Einstein Field Equations hold. As an illustration, a
model-independent analysis of 92 type Ia supernovae demonstrates that the curve
giving the expansion history has the wrong shape to be explained without some
form of dark energy or modified gravity. We discuss how upcoming lensing,
galaxy clustering, cosmic microwave background and Lyman alpha forest
observations can be combined to pursue this program, which generalizes the
quest for a dark energy equation of state, and forecast the accuracy that the
proposed SNAP satellite can attain.Comment: Replaced to match accepted PRD version. References and another
example added, section III omitted since superceded by astro-ph/0207047. 11
PRD pages, 7 figs. Color figs and links at
http://www.hep.upenn.edu/~max/gravity.html or from [email protected]