170 research outputs found
Tracking through equality
We give a tracker solution for the quintessence scalar field for
Ratra--Peebles or SUGRA potentials, holding before, during and after the
equality epoch (\rho_m=\rho_r) and nicely fitting the numerical behavior.Comment: submitted to New Astronom
Global cluster morphology and its evolution: X-ray data vs CDM, LCDM and mixed models
The global structure of galaxy clusters and its evolution are tested within a
large set of TREESPH simulations, so to allow a fair statistical comparison
with available X-ray data. Structure tests are based on the "power ratios",
introduced by Buote & Tsai. Cosmological models considered are CDM, LCDM
(Omega_L=0.7) and CHDM (1 mass.neu., Omega_h = 0.2). All models are normalized
to provide a fair number density of clusters. For each model we run a P3M
simulation in a large box, where we select the most massive 40 clusters. Going
back to the initial redshift we run a hydro-TREESPH simulation for each of
them. In this way we perform a statistical comparison of the global morphology
of clusters, for each cosmological model, with ROSAT data, using Student
t-test, F-test and K-S test. The last test and its generalization to 2--D
distributions are also used to compare the joint distributions of 2 or 3 power
ratios. We find that, using DM distribution, instead of gas, as done by some
authors, leads to biased results, as baryons are distributed in a less
structured way than DM. We also find that the cosmological models considered
have different behaviours in these tests: LCDM has the worst performance. CDM
and our CHDM have similar scores. The general trend of power ratio
distributions is already fit by these models, but a further improvement is
expected either from a different DM mix or a non-flat CDM model.Comment: 29 pages (LaTeX,macros included), 9 figure.ps & 3 tables included. To
appear on New Astronom
Mixed Dark Matter from Axino Distribution
We study the possibility of mixed dark matter obtained through the phase
space distribution of a single particle. An example is offered in the context
of SUSY models with a Peccei-Quinn symmetry. Axinos in the 100 keV range can
naturally have both thermal and non-thermal components. The latter one arises
from the lightest neutralino decays and derelativizes at z ~ 10^4.Comment: Figures added, references fixed. Version accepted for publication on
Phys. Rev. D. LaTeX. 9 pages, 3 figures, uses epsfig.st
Extending the Coyote emulator to dark energy models with standard - parametrization of the equation of state
We discuss an extension of the Coyote emulator to predict non-linear matter
power spectra of dark energy (DE) models with a scale factor dependent equation
of state of the form w = w_0 + ( 1 - a )w_a . The extension is based on the
mapping rule between non-linear spectra of DE models with constant equation of
state and those with time varying one originally introduced in ref. [40]. Using
a series of N-body simulations we show that the spectral equivalence is
accurate to sub-percent level across the same range of modes and redshift
covered by the Coyote suite. Thus, the extended emulator provides a very
efficient and accurate tool to predict non-linear power spectra for DE models
with w_0 - w_a parametrization. According to the same criteria we have
developed a numerical code, and we have implemented in a dedicated module for
the CAMB code, that can be used in combination with the Coyote Emulator in
likelihood analyses of non-linear matter power spectrum measurements. All codes
can be found at https://github.com/luciano-casarini/PKequalComment: All codes can be found at https://github.com/luciano-casarini/PKequa
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