1,029 research outputs found
Signature of short distance physics on inflation power spectrum and CMB anisotropy
The inflaton field responsible for inflation may not be a canonical
fundamental scalar. It is possible that the inflaton is a composite of fermions
or it may have a decay width. In these cases the standard procedure for
calculating the power spectrum is not applicable and a new formalism needs to
be developed to determine the effect of short range interactions of the
inflaton on the power spectrum and the CMB anisotropy. We develop a general
formalism for computing the power spectrum of curvature perturbations for such
non-canonical cases by using the flat space K\"all\'en-Lehmann spectral
function in curved quasi-de Sitter space assuming implicitly that the
Bunch-Davis boundary conditions enforces the inflaton mode functions to be
plane wave in the short wavelength limit and a complete set of mode functions
exists in quasi-de Sitter space. It is observed that the inflaton with a decay
width suppresses the power at large scale while a composite inflaton's power
spectrum oscillates at large scales. These observations may be vindicated in
the WMAP data and confirmed by future observations with PLANCK.Comment: 17 pages, 4 figures, Extended journal version, Accepted for
publication in JCA
Historia de Numancia en la que se explica todo lo acaecido durante su prolongada campaña de veinte años
Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-201
The Power Spectrum, Bias Evolution, and the Spatial Three-Point Correlation Function
We calculate perturbatively the normalized spatial skewness, , and full
three-point correlation function (3PCF), , induced by gravitational
instability of Gaussian primordial fluctuations for a biased tracer-mass
distribution in flat and open cold-dark-matter (CDM) models. We take into
account the dependence on the shape and evolution of the CDM power spectrum,
and allow the bias to be nonlinear and/or evolving in time, using an extension
of Fry's (1996) bias-evolution model. We derive a scale-dependent,
leading-order correction to the standard perturbative expression for in
the case of nonlinear biasing, as defined for the unsmoothed galaxy and
dark-matter fields, and find that this correction becomes large when probing
positive effective power-spectrum indices. This term implies that the inferred
nonlinear-bias parameter, as usually defined in terms of the smoothed density
fields, might depend on the chosen smoothing scale. In general, we find that
the dependence of on the biasing scheme can substantially outweigh that
on the adopted cosmology. We demonstrate that the normalized 3PCF, , is an
ill-behaved quantity, and instead investigate , the variance-normalized
3PCF. The configuration dependence of shows similarly strong
sensitivities to the bias scheme as , but also exhibits significant
dependence on the form of the CDM power spectrum. Though the degeneracy of
with respect to the cosmological parameters and constant linear- and
nonlinear-bias parameters can be broken by the full configuration dependence of
, neither statistic can distinguish well between evolving and non-evolving
bias scenarios. We show that this can be resolved, in principle, by considering
the redshift dependence of .Comment: 41 pages, including 12 Figures. To appear in The Astrophysical
Journal, Vol. 521, #
Optimal Constraints on Local Primordial Non-Gaussianity from the Two-Point Statistics of Large-Scale Structure
One of the main signatures of primordial non-Gaussianity of the local type is
a scale-dependent correction to the bias of large-scale structure tracers such
as galaxies or clusters, whose amplitude depends on the bias of the tracers
itself. The dominant source of noise in the power spectrum of the tracers is
caused by sampling variance on large scales (where the non-Gaussian signal is
strongest) and shot noise arising from their discrete nature. Recent work has
argued that one can avoid sampling variance by comparing multiple tracers of
different bias, and suppress shot noise by optimally weighting halos of
different mass. Here we combine these ideas and investigate how well the
signatures of non-Gaussian fluctuations in the primordial potential can be
extracted from the two-point correlations of halos and dark matter. On the
basis of large -body simulations with local non-Gaussian initial conditions
and their halo catalogs we perform a Fisher matrix analysis of the two-point
statistics. Compared to the standard analysis, optimal weighting- and
multiple-tracer techniques applied to halos can yield up to one order of
magnitude improvements in \fnl-constraints, even if the underlying dark
matter density field is not known. We compare our numerical results to the halo
model and find satisfactory agreement. Forecasting the optimal
\fnl-constraints that can be achieved with our methods when applied to
existing and future survey data, we find that a survey of
volume resolving all halos down to 10^{11}\hMsun at
will be able to obtain \sigma_{\fnl}\sim1 (68% cl), a factor of
improvement over the current limits. Decreasing the minimum mass of
resolved halos, increasing the survey volume or obtaining the dark matter maps
can further improve these limits, potentially reaching the level of
\sigma_{\fnl}\sim0.1. (abridged)Comment: V1: 23 pages, 12 figures, submitted to PRD. V2: 24 pages, added
appendix and citations, matched to PRD published versio
Observational signatures of Jordan-Brans-Dicke theories of gravity
We analyze the Jordan-Brans-Dicke model (JBD) of gravity, where deviations
from General Relativity (GR) are described by a scalar field non-minimally
coupled to gravity. The theory is characterized by a constant coupling
parameter, ; GR is recovered in the limit . In such theories, gravity modifications manifest at early times,
so that one cannot rely on the usual approach of looking for inconsistencies in
the expansion history and perturbations growth in order to discriminate between
JBD and GR. However, we show that a similar technique can be successfully
applied to early and late times observables instead. Cosmological parameters
inferred extrapolating early-time observations to the present will match those
recovered from direct late-time observations only if the correct gravity theory
is used. We use the primary CMB, as will be seen by the Planck satellite, as
the early-time observable; and forthcoming and planned Supernov{\ae}, Baryonic
Acoustic Oscillations and Weak Lensing experiments as late-time observables. We
find that detection of values of as large as 500 and 1000 is
within reach of the upcoming (2010) and next-generation (2020) experiments,
respectively.Comment: minor revision, references added, matching version published in JCA
Study of exclusive semileptonic and nonleptonic decays of B-c(-) in a nonrelativistic quark model
We present results for different observables measured in semileptonic and nonleptonic decays of the B-c(-) meson. The calculations have been done within the framework of a nonrelativistic constituent quark model. In order to check the sensitivity of all our results against the interquark interaction we use five different quark-quark potentials. We obtain form factors, decay widths, and asymmetry parameters for semileptonic B-c(-)-> c (c) over bar and B-c(-)->(B) over bar decays. In the limit of infinite heavy quark mass, our model reproduces the constraints of heavy quark spin symmetry. For the actual heavy quark masses we find nonetheless large corrections to that limiting situation for some form factors. We also analyze exclusive nonleptonic two-meson decay channels within the factorization approximation
Coupled dark matter-dark energy in light of near Universe observations
Cosmological analysis based on currently available observations are unable to
rule out a sizeable coupling among the dark energy and dark matter fluids. We
explore a variety of coupled dark matter-dark energy models, which satisfy
cosmic microwave background constraints, in light of low redshift and near
universe observations. We illustrate the phenomenology of different classes of
dark coupling models, paying particular attention in distinguishing between
effects that appear only on the expansion history and those that appear in the
growth of structure. We find that while a broad class of dark coupling models
are effectively models where general relativity (GR) is modified --and thus can
be probed by a combination of tests for the expansion history and the growth of
structure--, there is a class of dark coupling models where gravity is still
GR, but the growth of perturbations is, in principle modified. While this
effect is small in the specific models we have considered, one should bear in
mind that an inconsistency between reconstructed expansion history and growth
may not uniquely indicate deviations from GR. Our low redshift constraints
arise from cosmic velocities, redshift space distortions and dark matter
abundance in galaxy voids. We find that current data constrain the
dimensionless coupling to be |xi|<0.2, but prospects from forthcoming data are
for a significant improvement. Future, precise measurements of the Hubble
constant, combined with high-precision constraints on the growth of structure,
could provide the key to rule out dark coupling models which survive other
tests. We shall exploit as well weak equivalence principle violation arguments,
which have the potential to highly disfavour a broad family of coupled models.Comment: 34 pages, 6 figures; changes to match published versio
Co-occurrence and character convergence in two Neotropical bats
When functionally similar species co-occur, they are expected to differ in at least 1 niche axis to avoid competition. In bats, small differences in body size can influence ecology, potentially reducing niche overlap. We used yellow-shouldered bats (genus Sturnira) in Mexico as a model to investigate whether interspecific differences in body size increase when 2 related and ecologically similar species occur in sympatry. We hypothesized that size divergence would take place in sympatry, following known patterns whereby larger bats eat larger fruits and smaller bats forage and roost in more cluttered habitats. We collected data on body mass, forearm length, and skull size from museum specimens to characterize the overall dimensions of these bats. Using linear mixed effect models and permutation tests, we tested for differences between areas where these species occur in sympatry or allopatry, while controlling for the confounding effect of environmental variables and sexual dimorphism. Contrary to our original hypothesis, we detected size convergence in sympatric areas, an uncommon pattern in bats. We found no evidence of character displacement for forearm length and body mass, but an effect of co-occurrence on overall skull size and head length. Convergence in overall skull dimensions may reflect shared environmental pressures and similar food resources, which may not represent a limiting factor. Interspecific differences in forearm length remain constant in sympatry or allopatry. These differences likely preceded the 2 species coming into contact and could have allowed initial and ongoing coexistence by influencing wing properties and flight. We highlight the need for multivariate approaches in the study of character displacement, as selective pressures can act differently on different traits allowing both local adaptation and coexistence
In vitro study of antiamoebic activity of methanol extract of fruit of Pimpinella anisum on trophozoites of Entamoeba histolytica HM1-IMSS
The aniseed plant Pimpinella anisum (Saunf-Hindi) is one of the most ancient medicinal plants used by man. Currently, this plant has several uses in the food industry as spice, whereas in the pharmacopoeia, it is used as an expectorant in digestive disturbances, as mild diuretic, and as insect repellent in external use. In this paper, we evaluated the biological activity of methanolic extract of P. anisum on in vitro growth of Entamoeba histolytica HM1-IMSS under axenic conditions. We observed that the growth inhibition of E. histolytica was at CI50 = 0.034 μg/mL. Results confirm the antiamoebic activity of the methanolic extract of P. anisum.Keywords: Pimpinella anisum, Entamoeba histolytica, antiamoebic activity, medicinal plantsAfrican Journal of Biotechnology Vol. 12(16), pp. 2065-206
- …