156 research outputs found
Mass-Varying Neutrinos from a Variable Cosmological Constant
We consider, in a completely model-independent way, the transfer of energy
between the components of the dark energy sector consisting of the cosmological
constant (CC) and that of relic neutrinos. We show that such a cosmological
setup may promote neutrinos to mass-varying particles, thus resembling a
recently proposed scenario of Fardon, Nelson, and Weiner (FNW), but now without
introducing any acceleronlike scalar fields. Although a formal similarity of
the FNW scenario with the variable CC one can be easily established, one
nevertheless finds different laws for neutrino mass variation in each scenario.
We show that as long as the neutrino number density dilutes canonically, only a
very slow variation of the neutrino mass is possible. For neutrino masses to
vary significantly (as in the FNW scenario), a considerable deviation from the
canonical dilution of the neutrino number density is also needed. We note that
the present `coincidence' between the dark energy density and the neutrino
energy density can be obtained in our scenario even for static neutrino masses.Comment: 8 pages, minor corrections, two references added, to apear in JCA
Primordial Power Spectrum Reconstruction
In order to reconstruct the initial conditions of the universe it is
important to devise a method that can efficiently constrain the shape of the
power spectrum of primordial matter density fluctuations in a model-independent
way from data. In an earlier paper we proposed a method based on the wavelet
expansion of the primordial power spectrum. The advantage of this method is
that the orthogonality and multiresolution properties of wavelet basis
functions enable information regarding the shape of to be
encoded in a small number of non-zero coefficients. Any deviation from
scale-invariance can then be easily picked out. Here we apply this method to
simulated data to demonstrate that it can accurately reconstruct an input
, and present a prescription for how this method should be used
on future data.Comment: 4 pages, 2 figures. JCAP accepted versio
The Adiabatic Instability on Cosmology's Dark Side
We consider theories with a nontrivial coupling between the matter and dark
energy sectors. We describe a small scale instability that can occur in such
models when the coupling is strong compared to gravity, generalizing and
correcting earlier treatments. The instability is characterized by a negative
sound speed squared of an effective coupled dark matter/dark energy fluid. Our
results are general, and applicable to a wide class of coupled models and
provide a powerful, redshift-dependent tool, complementary to other
constraints, with which to rule many of them out. A detailed analysis and
applications to a range of models are presented in a longer companion paper.Comment: 4 pages, 1 figur
Cosmology with CMB anisotropy
Measurements of CMB anisotropy and, more recently, polarization have played a
very important role allowing precise determination of various parameters of the
`standard' cosmological model. The expectation of the paradigm of inflation and
the generic prediction of the simplest realization of inflationary scenario in
the early universe have also been established -- `acausally' correlated initial
perturbations in a flat, statistically isotropic universe, adiabatic nature of
primordial density perturbations. Direct evidence for gravitational instability
mechanism for structure formation from primordial perturbations has been
established. In the next decade, future experiments promise to strengthen these
deductions and uncover the remaining crucial signature of inflation -- the
primordial gravitational wave background.Comment: Plenary talk at the IXth. International Workshop on High Energy
Physics Phenomenology (WHEPP-9), Institute of Physics, Bhubaneshwar, India.
Jan 3-14, 2006; To appear in the Proceedings to be published in Pramana; 12
pages, 2 figure
Stationary dark energy: the present universe as a global attractor
We propose a cosmological model that makes a significant step toward solving
the coincidence problem of the near similarity at the present of the dark
energy and dark matter components. Our cosmology has the following properties:
a) among flat and homogeneous spaces, the present universe is a global
attractor: all the possible initial conditions lead to the observed proportion
of dark energy and dark matter; once reached, it remains fixed forever; b) the
expansion is accelerated at the present, as requested by the supernovae
observations; c) the model is consistent with the large-scale structure and
microwave background data; d) the dark energy and the dark matter densities
always scale similarly after equivalence and are close to within two orders of
magnitude. The model makes use of a non-linear coupling of the dark energy to
the dark matter that switches on after structure formation.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Lett. Minor revision
(added some refs, shortened to match PRL requirements
EMMA—mouse mutant resources for the international scientific community
The laboratory mouse is the premier animal model for studying human disease and thousands of mutants have been identified or produced, most recently through gene-specific mutagenesis approaches. High throughput strategies by the International Knockout Mouse Consortium (IKMC) are producing mutants for all protein coding genes. Generating a knock-out line involves huge monetary and time costs so capture of both the data describing each mutant alongside archiving of the line for distribution to future researchers is critical. The European Mouse Mutant Archive (EMMA) is a leading international network infrastructure for archiving and worldwide provision of mouse mutant strains. It operates in collaboration with the other members of the Federation of International Mouse Resources (FIMRe), EMMA being the European component. Additionally EMMA is one of four repositories involved in the IKMC, and therefore the current figure of 1700 archived lines will rise markedly. The EMMA database gathers and curates extensive data on each line and presents it through a user-friendly website. A BioMart interface allows advanced searching including integrated querying with other resources e.g. Ensembl. Other resources are able to display EMMA data by accessing our Distributed Annotation System server. EMMA database access is publicly available at http://www.emmanet.org
Planck 2013 results. XXII. Constraints on inflation
We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be ns = 0:9603 _ 0:0073, ruling out exact scale invariance at over 5_: Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0:11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models, preferring potentials with V00 < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n _ 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dns=dln k = 0:0134 _ 0:0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by __2 e_ _ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the _2 e_ by approximately 4 as a result of slightly lowering the theoretical prediction for the ` <_ 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions
Distribution function approach to redshift space distortions. Part II: N-body simulations
Measurement of redshift-space distortions (RSD) offers an attractive method
to directly probe the cosmic growth history of density perturbations. A
distribution function approach where RSD can be written as a sum over density
weighted velocity moment correlators has recently been developed. We use Nbody
simulations to investigate the individual contributions and convergence of this
expansion for dark matter. If the series is expanded as a function of powers of
mu, cosine of the angle between the Fourier mode and line of sight, there are a
finite number of terms contributing at each order. We present these terms and
investigate their contribution to the total as a function of wavevector k. For
mu^2 the correlation between density and momentum dominates on large scales.
Higher order corrections, which act as a Finger-of-God (FoG) term, contribute
1% at k~0.015h/Mpc, 10% at k~0.05h/Mpc at z=0, while for k>0.15h/Mpc they
dominate and make the total negative. These higher order terms are dominated by
density-energy density correlations which contribute negatively to the power,
while the contribution from vorticity part of momentum density auto-correlation
is an order of magnitude lower. For mu^4 term the dominant term on large scales
is the scalar part of momentum density auto-correlation, while higher order
terms dominate for k>0.15h/Mpc. For mu^6 and mu^8 we find it has very little
power for k<0.15h/Mpc. We also compare the expansion to the full 2D P^ss(k,mu)
as well as to their multipoles. For these statistics an infinite number of
terms contribute and we find that the expansion achieves percent level accuracy
for kmu<0.15h/Mpc at 6th order, but breaks down on smaller scales because the
series is no longer perturbative. We explore resummation of the terms into FoG
kernels, which extend the convergence up to a factor of 2 in scale. We find
that the FoG kernels are approximately Lorentzian.Comment: 21 pages, 9 figures, published in JCA
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