6,960 research outputs found
Constraints on inflation revisited: An analysis including the latest local measurement of the Hubble constant
We revisit the constraints on inflation models by using the current
cosmological observations involving the latest local measurement of the Hubble
constant ( km s Mpc). We constrain the
primordial power spectra of both scalar and tensor perturbations with the
observational data including the Planck 2015 CMB full data, the BICEP2 and Keck
Array CMB B-mode data, the BAO data, and the direct measurement of . In
order to relieve the tension between the local determination of the Hubble
constant and the other astrophysical observations, we consider the additional
parameter in the cosmological model. We find that, for the
CDM++ model, the scale invariance is only excluded at
the 3.3 level, and is favored at the 1.6
level. Comparing the obtained 1 and 2 contours of
with the theoretical predictions of selected inflation models, we find that
both the convex and concave potentials are favored at 2 level, the
natural inflation model is excluded at more than 2 level, the
Starobinsky inflation model is only favored at around 2 level,
and the spontaneously broken SUSY inflation model is now the most favored
model.Comment: 10 pages, 6 figure
Constraining dark energy with Hubble parameter measurements: an analysis including future redshift-drift observations
Dark energy affects the Hubble expansion rate (namely, the expansion history)
by an integral over . However, the usual observables are the
luminosity distances or the angular diameter distances, which measure the
distance-redshift relation. Actually, dark energy affects the distances (and
the growth factor) by a further integration over functions of . Thus, the
direct measurements of the Hubble parameter at different redshifts are
of great importance for constraining the properties of dark energy. In this
paper, we show how the typical dark energy models, for example, the
CDM, CDM, CPL, and holographic dark energy (HDE) models, can be
constrained by the current direct measurements of (31 data in total,
covering the redshift range of ). In fact, the future
redshift-drift observations (also referred to as the Sandage-Loeb test) can
also directly measure at higher redshifts, covering the range of . We thus discuss what role the redshift-drift observations can play in
constraining dark energy with the Hubble parameter measurements. We show that
the constraints on dark energy can be improved greatly with the data
from only a 10-year observation of redshift drift.Comment: 20 pages, 5 figures; final version published in EPJ
Exploring the evolution of color-luminosity parameter and its effects on parameter estimation
It has been found in previous studies that, for the Supernova Legacy Survey
three-year (SNLS3) data, there is strong evidence for the redshift-evolution of
color-luminosity parameter . In this paper, using three simplest dark
energy models (CDM, CDM, and CPL), we further explore the evolution
of and its effects on parameter estimation. In addition to the SNLS3
data, we also take into account the Planck distance priors data, as well as the
latest galaxy clustering (GC) data extracted from SDSS DR7 and BOSS. We find
that, for all the models, adding a parameter of can reduce
by 36, indicating that is ruled out at
6 confidence levels. In other words, deviates from a constant
at 6 confidence levels. This conclusion is insensitive to the dark
energy models considered, showing the importance of considering the evolution
of in the cosmology-fits. Furthermore, it is found that varying
can significantly change the fitting results of various cosmological
parameters: using the SNLS3 data alone, varying yields a larger
for the CDM model; using the SNLS3+CMB+GC data, varying
yields a larger and a smaller for all the models.
Moreover, we find that these results are much closer to those given by the
CMB+GC data, compared to the cases of treating as a constant. This
indicates that considering the evolution of is very helpful for
reducing the tension between supernova and other cosmological observations.Comment: 11 pages, 9 figures, 2 tables; accepted for publication in Physical
Review D. arXiv admin note: text overlap with arXiv:1306.6423; and with
arXiv:1109.3172 by other author
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
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