37 research outputs found
Constraints on primordial isocurvature perturbations and spatial curvature by Bayesian model selection
We present posterior likelihoods and Bayesian model selection analysis for
generalized cosmological models where the primordial perturbations include
correlated adiabatic and cold dark matter isocurvature components. We perform
nested sampling with flat and, for the first time, curved spatial geometries of
the Universe, using data from the cosmic microwave background (CMB)
anisotropies, the Union supernovae (SN) sample and a combined measurement of
the integrated Sachs-Wolfe (ISW) effect. The CMB alone favors a 3% (positively
correlated) isocurvature contribution in both the flat and curved cases. The
non-adiabatic contribution to the observed CMB temperature variance is 0 <
alpha_T < 7% at 98% CL in the curved case. In the flat case, combining the CMB
with SN data artificially biases the result towards the pure adiabatic LCDM
concordance model, whereas in the curved case the favored level of
non-adiabaticity stays at 3% level with all combinations of data. However, the
ratio of Bayes factors, or Delta ln(evidence), is more than 5 points in favor
of the flat adiabatic LCDM model, which suggests that the inclusion of the 5
extra parameters of the curved isocurvature model is not supported by the
current data. The results are very sensitive to the second and third acoustic
peak regions in the CMB temperature angular power: therefore a careful
calibration of these data will be required before drawing decisive conclusions
on the nature of primordial perturbations. Finally, we point out that the odds
for the flat non-adiabatic model are 1:3 compared to the curved adiabatic
model. This may suggest that it is not much less motivated to extend the
concordance model with 4 isocurvature degrees of freedom than it is to study
the spatially curved adiabatic model.Comment: 15 pages, 5 figures. V2: References and future predictions added;
accepted by PR
Primordial non-Gaussianity from two curvaton decays
We study a model where two scalar fields, that are subdominant during
inflation, decay into radiation some time after inflation has ended but before
primordial nucleosynthesis. Perturbations of these two curvaton fields can be
responsible for the primordial curvature perturbation. We write down the full
non-linear equations that relate the primordial perturbation to the curvaton
perturbations on large scales, calculate the power spectrum of the primordial
perturbation, and finally go to second order to find the non-linearity
parameter, fNL. We find large positive values of fNL if the energy densities of
the curvatons are sub-dominant when they decay, as in the single curvaton case.
But we also find a large fNL even if the curvatons dominate the total energy
density in the case when the inhomogeneous radiation produced by the first
curvaton decay is diluted by the decay of a second nearly homogeneous curvaton.
The minimum value min(fNL)=-5/4 which we find is the same as in the
single-curvaton case.Comment: 20 pages, 5 figure
Correlated isocurvature perturbations from mixed inflatonâcurvaton decay
We study cosmological perturbations in the case in which present-day matter consists of a mixture of inflaton and curvaton decay products. We calculate how the curvaton perturbations are transferred to its decay products in the general case when it does not behave like dust. Taking into account that the decay products of the inflaton can also have perturbations results in an interesting mixture of correlated adiabatic and isocurvature perturbations. In particular, negative correlation can improve the fit to the CMB data by lowering the angular power in the SachsâWolfe plateau without changing the peak structure. We do an 11-parameter fit to the WMAP data. We find that the best fit is not the âconcordance modelâ, and that well-fitting models do not cluster around the best fit, so cosmological parameters cannot be reliably estimated. We also find that in our model the mean quadrupole (l = 2) power is l(l+1)Cl/2Ï = 1081Â ÎŒK2, much lower than in the pure adiabatic ÎCDM model, which gives 1262Â ÎŒK2.Peer reviewe
Interacting Dark Energy -- constraints and degeneracies
In standard cosmologies, dark energy interacts only gravitationally with dark
matter. There could be a non-gravitational interaction in the dark sector,
leading to changes in the effective DE equation of state, in the redshift
dependence of the DM density and in structure formation. We use CMB, BAO and
SNIa data to constrain a model where the energy transfer in the dark sector is
proportional to the DE density. There are two subclasses, defined by the
vanishing of momentum transfer either in the DM or the DE frame. We conduct a
Markov-Chain Monte-Carlo analysis to obtain best-fit parameters. The background
evolution allows large interaction strengths, and the constraints from CMB
anisotropies are weak. The growth of DM density perturbations is much more
sensitive to the interaction, and can deviate strongly from the standard case.
However, the deviations are degenerate with galaxy bias and thus more difficult
to constrain. Interestingly, the ISW signature is suppressed since the
non-standard background evolution can compensate for high growth rates. We also
discuss the partial degeneracy between interacting DE and modified gravity, and
how this can be broken.Comment: 12 pages, 18 figures. Clarification on instabilities. Accepted by PR
Correlated Primordial Perturbations in Light of CMB and LSS Data
We use cosmic microwave background (CMB) and large-scale structure data to
constrain cosmological models where the primordial perturbations have both an
adiabatic and a cold dark matter (CDM) isocurvature component. We allow for a
possible correlation between the adiabatic and isocurvature modes, and for
different spectral indices for the power in each mode and for their
correlation. We do a likelihood analysis with 11 independent parameters. We
discuss the effect of choosing the pivot scale for the definition of amplitude
parameters. The upper limit for the isocurvature fraction is 18% around a pivot
scale k = 0.01 Mpc^{-1}. For smaller pivot wavenumbers the limit stays about
the same. For larger pivot wavenumbers, very large values of the isocurvature
spectral index are favored, which makes the analysis problematic, but larger
isocurvature fractions seem to be allowed. For large isocurvature spectral
indices n_iso > 2 a positive correlation between the adiabatic and isocurvature
mode is favored, and for n_iso < 2 a negative correlation is favored. The upper
limit to the nonadiabatic contribution to the CMB temperature variance is 7.5%.
Of the standard cosmological parameters, determination of the CDM density
and the sound horizon angle (or the Hubble constant )
are affected most by a possible presence of a correlated isocurvature
contribution. The baryon density nearly retains its ``adiabatic
value''.Comment: 20 pages, 21 figures (many in color
Testing distance duality with CMB anisotropies
We constrain deviations of the form T proportional to (1 + z)(1+epsilon) from the standard redshift-temperature relation, corresponding to modifying distance duality as D-L = (1 + z)(2(1+epsilon)) D-A. We consider a consistent model, in which both the background and perturbation equations are changed. For this purpose, we introduce a species of dark radiation particles to which photon energy density is transferred, and assume epsilon >= 0. The Planck 2015 release high multipole temperature plus low multipole data give the limit epsilon <4.5 x 10(-3) at 95% C.L. The main obstacle to improving this CMB-only result is strong degeneracy between and the physical matter densities omega(b) and omega(c). A constraint on deuterium abundance improves the limit to epsilon <1.8 x 10(-3). Adding the Planck high-multipole CMB polarisation and BAO data leads to a small improvement; with this maximal dataset we obtain epsilon <1.3 x 10(-3). This dataset constrains the present dark radiation energy density to at most 12% of the total photon plus dark radiation density. Finally, we discuss the degeneracy between dark radiation and the effective number of relativistic species N-eff, and consider the impact of dark radiation perturbations and allowing epsilon <0 on the results.Peer reviewe
Novel CMB constraints on the parameter in alpha-attractor models
Cosmological -attractors are a compelling class of inflationary
models. They lead to universal predictions for large-scale observables, broadly
independent from the functional form of the inflaton potential. In this work we
derive improved analytical predictions for the large-scale observables, whose
dependence on the duration of reheating and the parameter is made
explicit. We compare these with Planck and BICEP/Keck 2018 data in the
framework of a Bayesian study, employing uniform logarithmic and linear priors
for . Our improved universal predictions allow direct constraints on
the duration of reheating. Furthermore, while it is well-known that CMB
constraints on the tensor-to-scalar ratio can be used to place an upper bound
on the parameter, we demonstrate that including the
-dependence of the scalar spectral tilt yields novel constraints on
. In particular, for small , the scalar spectral tilt scales
with , regardless of the specific potential shape. For
decreasing , this eventually puts the models in tension with CMB
measurements, bounding the magnitude of from below. Therefore, in
addition to the upper bound from the tensor-to-scalar ratio, we derive the
first lower bound on the magnitude of for -attractor T-models,
at C.L. .Comment: version accepted for publication in JCA
Correlated adiabatic and isocurvature CMB fluctuations in the wake of the WMAP
In general correlated models, in addition to the usual adiabatic component
with a spectral index n_ad1 there is another adiabatic component with a
spectral index n_ad2 generated by entropy perturbation during inflation. We
extend the analysis of a correlated mixture of adiabatic and isocurvature CMB
fluctuations of the WMAP group, who set the two adiabatic spectral indices
equal. Allowing n_ad1 and n_ad2 to vary independently we find that the WMAP
data favor models where the two adiabatic components have opposite spectral
tilts. Using the WMAP data only, the 2-sigma upper bound for the isocurvature
fraction f_iso of the initial power spectrum at k_0=0.05 Mpc^{-1} increases
somewhat, e.g., from 0.76 of n_ad2 = n_ad1 models to 0.84 with a prior n_iso <
1.84 for the isocurvature spectral index. We also comment on a possible
degeneration between the correlation component and the optical depth tau.
Moreover, the measured low quadrupole in the TT angular power could be achieved
by a strong negative correlation, but then one needs a large tau to fit the TE
spectrum.Comment: 5 pages, 7 figures. V2: Added 2 figures and revised a bit the results
section. This is a slightly longer version than the published one in PR