2,216 research outputs found
Exploring the full parameter space for an interacting dark energy model with recent observations including redshift-space distortions: Application of the parametrized post-Friedmann approach
Dark energy can modify the dynamics of dark matter if there exists a direct
interaction between them. Thus a measurement of the structure growth, e.g.,
redshift-space distortions (RSD), can provide a powerful tool to constrain the
interacting dark energy (IDE) models. For the widely studied model, previous works showed that only a very small coupling
() can survive in current RSD data. However, all
these analyses had to assume and due to the existence of the
large-scale instability in the IDE scenario. In our recent work [Phys. Rev. D
90, 063005 (2014)], we successfully solved this large-scale instability problem
by establishing a parametrized post-Friedmann (PPF) framework for the IDE
scenario. So we, for the first time, have the ability to explore the full
parameter space of the IDE models. In this work, we reexamine the observational
constraints on the model within the PPF framework. By
using the Planck data, the baryon acoustic oscillation data, the JLA sample of
supernovae, and the Hubble constant measurement, we get
(). The fit result becomes
() once we further incorporate the
RSD data in the analysis. The error of is substantially reduced with
the help of the RSD data. Compared with the previous results, our results show
that a negative is favored by current observations, and a relatively
larger interaction rate is permitted by current RSD data.Comment: 12 pages, 3 figure
Measuring growth index in a universe with sterile neutrinos
Consistency tests for the general relativity (GR) can be performed by
constraining the growth index using the measurements of redshift-space
distortions (RSD) in conjunction with other observations. In previous studies,
deviations from the GR expected value of at the
2--3 level were found. In this work, we reconsider the measurement of
in a universe with sterile neutrinos. We constrain the sterile
neutrino cosmological model using the RSD measurements combined with the cosmic
microwave background data (Planck temperature data plus WMAP 9-yr polarization
data), the baryon acoustic oscillation data, the Hubble constant direct
measurement, the Planck Sunyaev-Zeldovich cluster counts data, and the galaxy
shear data. We obtain the constraint result of the growth index,
, well consistent with the GR expected value
(the consistency is at the 0.6 level). For the parameters of sterile
neutrino, we obtain and
eV. We also consider
the BICEP2 data and perform an analysis on the model with tensor modes. Similar
fit results are obtained, showing that once light sterile neutrino is
considered in the universe, GR will become well consistent with the current
observations.Comment: 5 pages, 3 figures; accepted for publication in Physics Letters
Testing models of vacuum energy interacting with cold dark matter
We test the models of vacuum energy interacting with cold dark matter and try
to probe the possible deviation from the CDM model using current
observations. We focus on two specific models, and
. The data combinations come from the Planck 2013 data, the
baryon acoustic oscillations measurements, the type-Ia supernovae data, the
Hubble constant measurement, the redshift space distortions data and the galaxy
weak lensing data. For the model, we find that it can be
tightly constrained by all the data combinations, while for the model, there still exist significant degeneracies between
parameters. The tightest constraints for the coupling constant are
(for ) and
(for ) at the level. For
all the fit results, we find that the null interaction is always
consistent with data. Our work completes the discussion on the interacting dark
energy model in the recent Planck 2015 papers. Considering this work together
with the Planck 2015 results, it is believed that there is no evidence for the
models beyond the standard CDM model from the point of view of
possible interaction.Comment: 7 pages, 2 figures; final version published in Physical Review
Probing cosmology with sterile neutrinos via measurements of scale-dependent growth rate of structure
In this paper, we constrain the dimensionless Compton wavelength parameter
of gravity as well as the mass of sterile neutrino by using the
cosmic microwave background observations, the baryon acoustic oscillation
surveys, and the linear growth rate measurements. Since both the model
and the sterile neutrino generally predict scale-dependent growth rates, we
utilize the growth rate data measured in different wavenumber bins with the
theoretical growth rate approximatively scale-independent in each bin. The
employed growth rate data come from the peculiar velocity measurements at
in five wavenumber bins, and the redshift space distortions measurements at
and in one wavenumber bin. By constraining the model
alone, we get a tight 95\% upper limit of . This result is
slightly weakened to (at 2 level) once we
simultaneously constrain the model and the sterile neutrino mass, due to
the degeneracy between the parameters of the two. For the massive sterile
neutrino parameters, we get the effective sterile neutrino mass
eV (2) and the effective
number of relativistic species (2) in the
model. As a comparison, we also obtain
eV (2) and (2) in the standard CDM
model.Comment: 6 pages, 3 figures; revised version accepted for publication in Phys.
Lett.
Sterile neutrinos help reconcile the observational results of primordial gravitational waves from Planck and BICEP2
We show that involving a sterile neutrino species in the CDM+
model can help relieve the tension about the tensor-to-scalar ratio between
the Planck temperature data and the BICEP2 B-mode polarization data. Such a
model is called the CDM++ model in this paper. Compared to
the CDM+ model, there are two extra parameters, and
, in the CDM++ model. We
show that in this model the tension between Planck and BICEP2 can be greatly
relieved at the cost of the increase of . However, comparing with the
CDM++ model that can significantly reduce the tension
between Planck and BICEP2 but also makes trouble to inflation due to the large
running of the spectral index of order produced, the
CDM++ model is much better for inflation. By including a
sterile neutrino species in the standard cosmology, besides the tension with
BICEP2, the other tensions of Planck with other astrophysical data, such as the
direct measurement, the Sunyaev-Zeldovich cluster counts, and the galaxy
shear data, can all be significantly relieved. So, this model seems to be an
economical choice. Combining the Planck temperature data, the WMAP-9
polarization data, and the baryon acoustic oscillation data with all these
astrophysical data (including BICEP2), we find that in the
CDM++ model , ,
and eV. Thus, our results prefer
at the 2.7 level and a nonzero mass of sterile neutrino at the
3.9 level.Comment: 5 pages, 3 figure
A global fit study on the new agegraphic dark energy model
We perform a global fit study on the new agegraphic dark energy (NADE) model
in a non-flat universe by using the MCMC method with the full CMB power spectra
data from the WMAP 7-yr observations, the SNIa data from Union2.1 sample, BAO
data from SDSS DR7 and WiggleZ Dark Energy Survey, and the latest measurements
of from HST. We find that the value of is greater than 0 at
least at the 3 confidence levels (CLs), which implies that the NADE
model distinctly favors an open universe. Besides, our results show that the
value of the key parameter of NADE model,
, at the 1--3 CLs,
where its best-fit value is significantly smaller than those obtained in
previous works. We find that the reason leading to such a change comes from the
different SNIa samples used. Our further test indicates that there is a
distinct tension between the Union2 sample of SNIa and other observations, and
the tension will be relieved once the Union2 sample is replaced by the Union2.1
sample. So, the new constraint result of the NADE model obtained in this work
is more reasonable than before.Comment: 6 pages, 3 figures; typos correcte
First Abundance Measurement of Organic Molecules in the Atmosphere of HH 212 Protostellar Disk
HH 212 is one of the well-studied protostellar systems, showing the first
vertically resolved disk with a warm atmosphere around the central protostar.
Here we report a detection of 9 organic molecules (including newly detected
ketene, formic acid, deuterated acetonitrile, methyl formate, and ethanol) in
the disk atmosphere, confirming that the disk atmosphere is, for HH 212, the
chemically rich component, identified before at a lower resolution as a
"hot-corino". More importantly, we report the first systematic survey and
abundance measurement of organic molecules in the disk atmosphere within
40 au of the central protostar. The relative abundances of these molecules are
similar to those in the hot corinos around other protostars and in Comet
Lovejoy. These molecules can be either (i) originally formed on icy grains and
then desorbed into gas phase or (ii) quickly formed in the gas phase using
simpler species ejected from the dust mantles. The abundances and spatial
distributions of the molecules provide strong constraints on models of their
formation and transport in star formation. These molecules are expected to form
even more complex organic molecules needed for life and deeper observations are
needed to find them.Comment: 12 pages, 4 figure
Redshift drift exploration for interacting dark energy
By detecting redshift drift in the spectra of Lyman- forest of
distant quasars, Sandage-Loeb (SL) test directly measures the expansion of the
universe, covering the "redshift desert" of . Thus this
method is definitely an important supplement to the other geometric
measurements and will play a crucial role in cosmological constraints. In this
paper, we quantify the ability of SL test signal by a CODEX-like spectrograph
for constraining interacting dark energy. Four typical interacting dark energy
models are considered: (i) , (ii) ,
(iii) , and (iv) . The results show
that for all the considered interacting dark energy models, relative to the
current joint SN+BAO+CMB+ observations, the constraints on and
would be improved by about 60\% and 30--40\%, while the constraints on
and would be slightly improved, with a 30-yr observation of SL
test. We also explore the impact of SL test on future joint geometric
observations. In this analysis, we take the model with as an
example, and simulate future SN and BAO data based on the space-based project
WFIRST. We find that in the future geometric constraints, the redshift drift
observations would help break the geometric degeneracies in a meaningful way,
thus the measurement precisions of , , , and could
be substantially improved using future probes.Comment: 6 pages, 5 figures; accepted for publication in EPJC. arXiv admin
note: text overlap with arXiv:1407.712
Neutrinos in the holographic dark energy model: constraints from latest measurements of expansion history and growth of structure
The model of holographic dark energy (HDE) with massive neutrinos and/or dark
radiation is investigated in detail. The background and perturbation evolutions
in the HDE model are calculated. We employ the PPF approach to overcome the
gravity instability difficulty (perturbation divergence of dark energy) led by
the equation-of-state parameter evolving across the phantom divide
in the HDE model with . We thus derive the evolutions of density
perturbations of various components and metric fluctuations in the HDE model.
The impacts of massive neutrino and dark radiation on the CMB anisotropy power
spectrum and the matter power spectrum in the HDE scenario are discussed.
Furthermore, we constrain the models of HDE with massive neutrinos and/or dark
radiation by using the latest measurements of expansion history and growth of
structure, including the Planck CMB temperature data, the baryon acoustic
oscillation data, the JLA supernova data, the Hubble constant direct
measurement, the cosmic shear data of weak lensing, the Planck CMB lensing
data, and the redshift space distortions data. We find that
eV (95\% CL) and in the HDE model from the
constraints of these data.Comment: 18 pages, 5 figures; revised version accepted for publication in JCA
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