621 research outputs found
Cluster Masses Accounting for Structure along the Line of Sight
Weak gravitational lensing of background galaxies by foreground clusters
offers an excellent opportunity to measure cluster masses directly without
using gas as a probe. One source of noise which seems difficult to avoid is
large scale structure along the line of sight. Here I show that, by using
standard map-making techniques, one can minimize the deleterious effects of
this noise. The resulting uncertainties on cluster masses are significantly
smaller than when large scale structure is not properly accounted for, although
still larger than if it was absent altogether.Comment: 5 pages, 5 figure
Effect of halo modelling on WIMP exclusion limits
WIMP direct detection experiments are just reaching the sensitivity required
to detect galactic dark matter in the form of neutralinos. Data from these
experiments are usually analysed under the simplifying assumption that the
Milky Way halo is an isothermal sphere with maxwellian velocity distribution.
Observations and numerical simulations indicate that galaxy halos are in fact
triaxial and anisotropic. Furthermore, in the cold dark matter paradigm
galactic halos form via the merger of smaller subhalos, and at least some
residual substructure survives. We examine the effect of halo modelling on WIMP
exclusion limits, taking into account the detector response. Triaxial and
anisotropic halo models, with parameters motivated by observations and
numerical simulations, lead to significant changes which are different for
different experiments, while if the local WIMP distribution is dominated by
small scale clumps then the exclusion limits are changed dramatically.Comment: 9 pages, 9 figures, version to appear in Phys. Rev. D, minor change
Microscopic study of the He2-SF6 trimers
The He2-SF6 trimers, in their different He isotopic combinations, are studied
both in the framework of the correlated Jastrow approach and of the Correlated
Hyperspherical Harmonics expansion method. The energetics and structure of the
He-SF6 dimers are analyzed, and the existence of a characteristic rotational
band in the excitation spectrum is discussed, as well as the isotopic
differences. The binding energies and the spatial properties of the trimers, in
their ground and lowest lying excited states, obtained by the Jastrow ansatz
are in excellent agreement with the results of the converged CHH expansion. The
introduction of the He-He correlation makes all trimers bound by largely
suppressing the short range He-He repulsion.
The structural properties of the trimers are qualitatively explained in terms
of the shape of the interactions, Pauli principle and masses of the
constituents.Comment: 17 pages, 5 figures. Submitted to PR
Alcalóides de Duguetia trunciflora Maas (Annonaceae)
From the ethanolic extract of the leaves and thin branches of Duguetia trunciflora Maas (Annonaceae) six alkaloids were isolated, being one benzylisoquinoline: reticuline¹, four tetrahydroprotoberberine:,tetrahydro-palmatine², tetrahydrojathrorrizine³, discretamine4, thaicanine5, and one berberine: jathrorrizine6. These alkaloids were identified through ¹H and 13C NMR spectroscopic technics. The alkaloids 1, 3, 5 and 6 are being cited for the first time on Duguetia genus
Two-dimensional clusters of liquid 4-He
The binding energies of two-dimensional clusters (puddles) of He are
calculated in the framework of the diffusion Monte Carlo method. The results
are very well fitted by a mass formula in powers of , where is
the number of particles. The analysis of the mass formula allows for the
extraction of the line tension, which turns out to be 0.121 K/A. Sizes and
density profiles of the puddles are also reported.Comment: 19 pages including 2 figs; revtex4. Matches published version: major
changes in section V: profiles are now calculated with an unbiased estimator.
Conclusions remain unchange
Inflation, cold dark matter, and the central density problem
A problem with high central densities in dark halos has arisen in the context
of LCDM cosmologies with scale-invariant initial power spectra. Although n=1 is
often justified by appealing to the inflation scenario, inflationary models
with mild deviations from scale-invariance are not uncommon and models with
significant running of the spectral index are plausible. Even mild deviations
from scale-invariance can be important because halo collapse times and
densities depend on the relative amount of small-scale power. We choose several
popular models of inflation and work out the ramifications for galaxy central
densities. For each model, we calculate its COBE-normalized power spectrum and
deduce the implied halo densities using a semi-analytic method calibrated
against N-body simulations. We compare our predictions to a sample of dark
matter-dominated galaxies using a non-parametric measure of the density. While
standard n=1, LCDM halos are overdense by a factor of 6, several of our example
inflation+CDM models predict halo densities well within the range preferred by
observations. We also show how the presence of massive (0.5 eV) neutrinos may
help to alleviate the central density problem even with n=1. We conclude that
galaxy central densities may not be as problematic for the CDM paradigm as is
sometimes assumed: rather than telling us something about the nature of the
dark matter, galaxy rotation curves may be telling us something about inflation
and/or neutrinos. An important test of this idea will be an eventual consensus
on the value of sigma_8, the rms overdensity on the scale 8 h^-1 Mpc. Our
successful models have values of sigma_8 approximately 0.75, which is within
the range of recent determinations. Finally, models with n>1 (or sigma_8 > 1)
are highly disfavored.Comment: 13 pages, 6 figures. Minor changes made to reflect referee's
Comments, error in Eq. (18) corrected, references updated and corrected,
conclusions unchanged. Version accepted for publication in Phys. Rev. D,
scheduled for 15 August 200
CMB-Cluster Lensing
Clusters of galaxies are powerful cosmological probes, particularly if their
masses can be determined. One possibility for mass determination is to study
the cosmic microwave background (CMB) on small angular scales and observe
deviations from a pure gradient due to lensing of massive clusters. I show
that, neglecting contamination, this technique has the power to determine
cluster masses very accurately, in agreement with estimates by Seljak and
Zaldarriaga (1999). However, the intrinsic small scale structure of the CMB
significantly degrades this power. The resulting mass constraints are useless
unless one imposes a prior on the concentration parameter c. With even a modest
prior on c, an ambitious CMB experiment (0.5' resolution and 1 microK per
pixel) could determine masses of high redshift (z>0.5) clusters with ~ 30%
accuracy.Comment: 17 pages, 10 figure
On Dark Matter Annihilation in the Local Group
Under the hypothesis of a Dark Matter composed by supersymmetric particles
like neutralinos, we investigate the possibility that their annihilation in the
haloes of nearby galaxies could produce detectable fluxes of -photons.
Expected fluxes depend on several, poorly known quantities such as the density
profiles of Dark Matter haloes, the existence and prominence of central density
cusps and the presence of a population of sub-haloes. We find that, for all
reasonable choices of Dark Matter halo models, the intensity of the
-ray flux from some of the nearest extragalactic objects, like M31, is
comparable or higher than the diffuse Galactic foreground. We show that next
generation ground-based experiments could have the sensitivity to reveal such
fluxes which could help us unveiling the nature of Dark Matter particles.Comment: 11 pages, 10 figures. Accepted for publication in Phys. Rev. D.;
added a new paragraph on the detectability of Galactic sub-halos in our
Galaxy; added a discussion on their model dependence. The relation of our
results with the "CDM crisis" issue has also been adde
The spacetime associated with galactic dark matter halos
We show how an adequate post--Newtonian generalization can be obtained for
Newtonian dark matter halos associated with an empiric density profile.
Applying this approach to halos that follow from the well known numerical
simulations of Navarro, Frenk and White (NFW), we derive all dynamical
variables and show that NFW halos approximatelly follow an ideal gas type of
equation of state which fits very well to a polytropic relation in the region
outside the core. This fact suggests that ``outer'' regions of NFW halos might
be related to equilibrium states in the non--extensive Statistical Mechanics
formalism proposed by Tsallis.Comment: 6 pages, 1 figur
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
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