7,414 research outputs found
Comparing holographic dark energy models with statefinder
We apply the statefinder diagnostic to the holographic dark energy models,
including the original holographic dark energy (HDE) model, the new holographic
dark energy model, the new agegraphic dark energy (NADE) model, and the Ricci
dark energy model. In the low-redshift region the holographic dark energy
models are degenerate with each other and with the CDM model in the
and evolutions. In particular, the HDE model is highly degenerate
with the CDM model, and in the HDE model the cases with different
parameter values are also in strong degeneracy. Since the observational data
are mainly within the low-redshift region, it is very important to break this
low-redshift degeneracy in the and diagnostics by using some
quantities with higher order derivatives of the scale factor. It is shown that
the statefinder diagnostic is very useful in breaking the low-redshift
degeneracies. By employing the statefinder diagnostic the holographic dark
energy models can be differentiated efficiently in the low-redshift region. The
degeneracy between the holographic dark energy models and the CDM
model can also be broken by this method. Especially for the HDE model, all the
previous strong degeneracies appearing in the and diagnostics are
broken effectively. But for the NADE model, the degeneracy between the cases
with different parameter values cannot be broken, even though the statefinder
diagnostic is used. A direct comparison of the holographic dark energy models
in the -- plane is also made, in which the separations between the models
(including the CDM model) can be directly measured in the light of the
current values of the models.Comment: 8 pages, 8 figures; accepted by European Physical Journal C; matching
the publication versio
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
Revisiting the holographic dark energy in a non-flat universe: alternative model and cosmological parameter constraints
We propose an alternative model for the holographic dark energy in a non-flat
universe. This new model differs from the previous one in that the IR length
cutoff is taken to be exactly the event horizon size in a non-flat
universe, which is more natural and theoretically/conceptually concordant with
the model of holographic dark energy in a flat universe. We constrain the model
using the recent observational data including the type Ia supernova data from
SNLS3, the baryon acoustic oscillation data from 6dF, SDSS-DR7, BOSS-DR11, and
WiggleZ, the cosmic microwave background data from Planck, and the Hubble
constant measurement from HST. In particular, since some previous studies have
shown that the color-luminosity parameter of supernovae is likely to
vary during the cosmic evolution, we also consider such a case that in
SNLS3 is time-varying in our data fitting. Compared to the constant
case, the time-varying case reduces the value of by about 35
and results in that deviates from a constant at about 5 level,
well consistent with the previous studies. For the parameter of the
holographic dark energy, the constant fit gives and
the time-varying fit yields . In addition, an open
universe is favored (at about 2) for the model by the current data.Comment: 8 pages, 4 figure
Design and optimization of joint iterative detection and decoding receiver for uplink polar coded SCMA system
SCMA and polar coding are possible candidates for 5G systems. In this paper, we firstly propose the joint iterative detection and decoding (JIDD) receiver for the uplink polar coded sparse code multiple access (PC-SCMA) system. Then, the EXIT chart is used to investigate the performance of the JIDD receiver. Additionally, we optimize the system design and polar code construction based on the EXIT chart analysis. The proposed receiver integrates the factor graph of SCMA detector and polar soft-output decoder into a joint factor graph, which enables the exchange of messages between SCMA detector and polar decoder iteratively. Simulation results demonstrate that the JIDD receiver has better BER performance and lower complexity than the separate scheme. Specifically, when polar code length N=256 and code rate R=1/2 , JIDD outperforms the separate scheme 4.8 and 6 dB over AWGN channel and Rayleigh fading channel, respectively. It also shows that, under 150% system loading, the JIDD receiver only has 0.3 dB performance loss compared to the single user uplink PC-SCMA over AWGN channel and 0.6 dB performance loss over Rayleigh fading channel
No evidence for the evolution of mass density power-law index from strong gravitational lensing observation
In this paper, we consider the singular isothermal sphere lensing model that
has a spherically symmetric power-law mass distribution . We investigate whether the mass density power-law index
is cosmologically evolutionary by using the strong gravitational lensing (SGL)
observation, in combination with other cosmological observations. We also check
whether the constraint result of is affected by the cosmological
model, by considering several simple dynamical dark energy models. We find that
the constraint on is mainly decided by the SGL observation and
independent of the cosmological model, and we find no evidence for the
evolution of from the SGL observation.Comment: 7 pages, 3 figure
Online Estimation with Rolling Validation: Adaptive Nonparametric Estimation with Stream Data
Online nonparametric estimators are gaining popularity due to their efficient
computation and competitive generalization abilities. An important example
includes variants of stochastic gradient descent. These algorithms often take
one sample point at a time and instantly update the parameter estimate of
interest. In this work we consider model selection and hyperparameter tuning
for such online algorithms. We propose a weighted rolling-validation procedure,
an online variant of leave-one-out cross-validation, that costs minimal extra
computation for many typical stochastic gradient descent estimators. Similar to
batch cross-validation, it can boost base estimators to achieve a better,
adaptive convergence rate. Our theoretical analysis is straightforward, relying
mainly on some general statistical stability assumptions. The simulation study
underscores the significance of diverging weights in rolling validation in
practice and demonstrates its sensitivity even when there is only a slim
difference between candidate estimators
- …