817 research outputs found
Statefinder hierarchy exploration of the extended Ricci dark energy
We apply the statefinder hierarchy plus the fractional growth parameter to
explore the extended Ricci dark energy (ERDE) model, in which there are two
independent coefficients and . By adjusting them, we plot
evolution trajectories of some typical parameters, including Hubble expansion
rate , deceleration parameter , the third and fourth order hierarchy
and and fractional growth parameter ,
respectively, as well as several combinations of them. For the case of variable
and constant , in the low-redshift region the evolution
trajectories of are in high degeneracy and that of separate somewhat.
However, the CDM model is confounded with ERDE in both of these two
cases. and , especially the former, perform much better.
They can differentiate well only varieties of cases within ERDE except
CDM in the low-redshift region. For high-redshift region, combinations
can break the degeneracy. Both of
and have the ability to
discriminate ERDE with from CDM, of which the degeneracy
cannot be broken by all the before-mentioned parameters. For the case of
variable and constant , and can
only discriminate ERDE from CDM. Nothing but pairs
and can discriminate not only
within ERDE but also ERDE from CDM. Finally we find that
is surprisingly a better choice to discriminate within ERDE itself, and ERDE
from CDM as well, rather than .Comment: 8 pages, 14 figures; published versio
A search for sterile neutrinos with the latest cosmological observations
We report the result of a search for sterile neutrinos with the latest
cosmological observations. Both cases of massless and massive sterile neutrinos
are considered in the CDM cosmology. The cosmological observations
used in this work include the Planck 2015 temperature and polarization data,
the baryon acoustic oscillation data, the Hubble constant direct measurement
data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck lensing
data, and the cosmic shear data. We find that the current observational data
give a hint of the existence of massless sterile neutrino (as dark radiation)
at the 1.44 level, and the consideration of an extra massless sterile
neutrino can indeed relieve the tension between observations and improve the
cosmological fit. For the case of massive sterile neutrino, the observations
give a rather tight upper limit on the mass, which implies that actually a
massless sterile neutrino is more favored. Our result is consistent with the
recent result of neutrino oscillation experiment done by the Daya Bay and MINOS
collaborations, as well as the recent result of cosmic ray experiment done by
the IceCube collaboration.Comment: 16 pages, 4 figures; accepted for publication in Eur. Phys. J.
Quantifying the impact of future Sandage-Loeb test data on dark energy constraints
The Sandage-Loeb (SL) test is a unique method to probe dark energy in the
"redshift desert" of , and thus it provides an important
supplement to the other dark energy probes. Therefore, it is of great
importance to quantify how the future SL test data impact on the dark energy
constraints. To avoid the potential inconsistency in data, we use the
best-fitting model based on the other geometric measurements as the fiducial
model to produce 30 mock SL test data. The 10-yr, 20-yr, and 30-yr observations
of SL test are analyzed and compared in detail. We show that compared to the
current combined data of type Ia supernovae, baryon acoustic oscillation,
cosmic microwave background, and Hubble constant, the 30-yr observation of SL
test could improve the constraint on by about and the
constraint on by about . Furthermore, the SL test can also improve the
measurement of the possible direct interaction between dark energy and dark
matter. We show that the SL test 30-yr data could improve the constraint on
by about and for the and models, respectively.Comment: 10 pages, 3 figure
Parameter estimation with Sandage-Loeb test
The Sandage-Loeb (SL) test directly measures the expansion rate of the
universe in the redshift range of by detecting redshift
drift in the spectra of Lyman- forest of distant quasars. We discuss
the impact of the future SL test data on parameter estimation for the
CDM, the CDM, and the CDM models. To avoid the potential
inconsistency with other observational data, we take the best-fitting dark
energy model constrained by the current observations as the fiducial model to
produce 30 mock SL test data. The SL test data provide an important supplement
to the other dark energy probes, since they are extremely helpful in breaking
the existing parameter degeneracies. We show that the strong degeneracy between
and in all the three dark energy models is well broken by the
SL test. Compared to the current combined data of type Ia supernovae, baryon
acoustic oscillation, cosmic microwave background, and Hubble constant, the
30-yr observation of SL test could improve the constraints on and
by more than 60\% for all the three models. But the SL test can only
moderately improve the constraint on the equation of state of dark energy. We
show that a 30-yr observation of SL test could help improve the constraint on
constant by about 25\%, and improve the constraints on and by
about 20\% and 15\%, respectively. We also quantify the constraining power of
the SL test in the future high-precision joint geometric constraints on dark
energy. The mock future supernova and baryon acoustic oscillation data are
simulated based on the space-based project JDEM. We find that the 30-yr
observation of SL test would help improve the measurement precision of
, , and by more than 70\%, 20\%, and 60\%, respectively,
for the CDM model.Comment: 16 pages, 9 figures, 3 tables; adding a new section to address future
SN and BAO observations; accepted for publication in JCA
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