10 research outputs found
Transients from Initial Conditions in Cosmological Simulations
We study the impact of setting initial conditions in numerical simulations
using the standard procedure based on the Zel'dovich approximation (ZA). As it
is well known from perturbation theory, ZA initial conditions have incorrect
second and higher-order growth and therefore excite long-lived transients in
the evolution of the statistical properties of density and velocity fields. We
also study the improvement brought by using more accurate initial conditions
based on second-order Lagrangian perturbation theory (2LPT). We show that 2LPT
initial conditions reduce transients significantly and thus are much more
appropriate for numerical simulations devoted to precision cosmology. Using
controlled numerical experiments with ZA and 2LPT initial conditions we show
that simulations started at redshift z_i=49 using the ZA underestimate the
power spectrum in the nonlinear regime by about 2,4,8 % at z=0,1,3
respectively, whereas the mass function of dark matter halos is underestimated
by 5% at m=10^15 M_sun/h (z=0) and 10% at m=2x10^14M_sun/h (z=1). The
clustering of halos is also affected to the few percent level at z=0. These
systematics effects are typically larger than statistical uncertainties in
recent mass function and power spectrum fitting formulae extracted from
numerical simulations. At large scales, the measured transients in higher-order
correlations can be understood from first principle calculations based on
perturbation theory.Comment: 14 pages, 14 figures, code to generate 2LPT initial conditions
available at http://cosmo.nyu.edu/roman/2LPT . Typos corrected, Fig.13
symbols consistent with Fig.11,1
Cosmology and the Bispectrum
The present spatial distribution of galaxies in the Universe is non-Gaussian, with 40% skewness in 50 Mpc/h spheres, and remarkably little is known about the information encoded in it about cosmological parameters beyond the power spectrum. In this work we present an attempt to bridge this gap by studying the bispectrum, paying particular attention to a joint analysis with the power spectrum and their combination with CMB data. We address the covariance properties of the power spectrum and bispectrum including the effects of beat coupling that lead to interesting cross-correlations, and discuss how baryon acoustic oscillations break degeneracies. We show that the bispectrum has significant information on cosmological parameters well beyond its power in constraining galaxy bias, and when combined with the power spectrum is more complementary than combining power spectra of different samples of galaxies, since non-Gaussianity provides a somewhat different direction in parameter space. In the framework of flat cosmological models we show that most of the improvement of adding bispectrum information corresponds to parameters related to the amplitude and effective spectral index of perturbations, which can be improved by almost a factor of two. Moreover, we demonstrate that the expected statistical uncertainties in sigma8 of a few percent are robust to relaxing the dark energy beyond a cosmological constant
Un modelo simple de propagación de incendios forestales con ecuaciones diferenciales ordinarias
Artículo fotocopiado. No existe versión digital.
Licencia Creative Commons. Atribución 3.0 España (CC BY 3.0 ES)Pueblas, S.; García Raffi, LM.; Sánchez Pérez, EA.; Sánchez Pérez, JV. (2001). Un modelo simple de propagación de incendios forestales con ecuaciones diferenciales ordinarias. Epsilon. 51:489-502. http://hdl.handle.net/10251/60373S4895025
The Schrdinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics
In this paper it is argued how the dynamics of the classical Newtonian N-body
system can be described in terms of the Schrdinger-Poisson equations
in the large limit. This result is based on the stochastic quantization
introduced by Nelson, and on the Calogero conjecture. According to the Calogero
conjecture, the emerging effective Planck constant is computed in terms of the
parameters of the N-body system as , where is the gravitational constant, and are the
number and the mass of the bodies, and is their average density. The
relevance of this result in the context of large scale structure formation is
discussed. In particular, this finding gives a further argument in support of
the validity of the Schrdinger method as numerical double of the
N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.
The Signature of Large Scale Structures on the Very High Energy Gamma-Ray Sky
If the diffuse extragalactic gamma ray emission traces the large scale
structures of the universe, peculiar anisotropy patterns are expected in the
gamma ray sky. In particular, because of the cutoff distance introduced by the
absorption of 0.1-10 TeV photons on the infrared/optical background, prominent
correlations with the local structures within a range of few hundreds Mpc
should be present. We provide detailed predictions of the signal based on the
PSCz map of the local universe. We also use mock N-body catalogues complemented
with the halo model of structures to study some statistical features of the
expected signatures. The results are largely independent from cosmological
details, and depend mostly on the index of correlation (or bias) of the sources
with respect to the large scale distribution of galaxies. For instance, the
predicted signal in the case of a quadratic correlation (as it may happen for a
dark matter annihilation contribution to the diffuse gamma flux) differs
substantially from a linear correlation case, providing a complementary tool to
unveil the nature of the sources of the diffuse gamma ray emission. The chances
of the present and future space and ground based observatories to measure these
features are discussed.Comment: 26 pages, 9 figures; matches published versio
A Gamma-adapted subunit vaccine induces broadly neutralizing antibodies against SARS-CoV-2 variants and protects mice from infection
Abstract In the context of continuous emergence of SARS-CoV-2 variants of concern (VOCs), one strategy to prevent the severe outcomes of COVID-19 is developing safe and effective broad-spectrum vaccines. Here, we present preclinical studies of a RBD vaccine derived from the Gamma SARS-CoV-2 variant adjuvanted with Alum. The Gamma-adapted RBD vaccine is more immunogenic than the Ancestral RBD vaccine in terms of inducing broader neutralizing antibodies. The Gamma RBD presents more immunogenic B-cell restricted epitopes and induces a higher proportion of specific-B cells and plasmablasts than the Ancestral RBD version. The Gamma-adapted vaccine induces antigen specific T cell immune responses and confers protection against Ancestral and Omicron BA.5 SARS-CoV-2 challenge in mice. Moreover, the Gamma RBD vaccine induces higher and broader neutralizing antibody activity than homologous booster vaccination in mice previously primed with different SARS-CoV-2 vaccine platforms. Our study indicates that the adjuvanted Gamma RBD vaccine is highly immunogenic and a broad-spectrum vaccine candidate