1,636 research outputs found
FRCAMB: An Code for Anisotropies in the Microwave Background
An gravity model is proposed to realize a late time accelerated
expansion of our Universe. To test the viability of an gravity model
through cosmic observations, the background evolution and the
Einstein-Boltzmann equation should be solved for studying the effects on the
cosmic microwave background power spectrum and on the matter power spectrum. In
the market, we already have the modified versions of {\bf CAMB} code, for
instance {\bf EFTCAMB} and {\bf MGCAMB}. However, in these publicly available
Einstein-Boltzmann codes, a specific background cosmology, for example the
CDM or CDM, is assumed. This assumption would be non-proper for a
specific model where the background evolution may be different from a
CDM cosmology. Therefore the main task for this paper is to present a
code to calculate the anisotropies in the microwave background for any
gravity model based on {\bf CAMB} code, i.e. {\bf FRCAMB}, where the background
and perturbation evolutions are included consistently. As results, one can
treat {\bf FRCAMB} as a blackbox to output the CMB power spectrum and matter
power spectrum, once an function, its first two derivative with respect
to , i.e. , and the reasonable
values of the model parameters are inputted properly. As by-products, one can
also output the effective equation of state of model, the evolution of
the dimensionless energy densities and other interesting cosmological
quantities.Comment: 8 pages, 7 figure
Unified Dark Fluid with Constant Adiabatic Sound Speed: Including Entropic Perturbations
In this paper, we continue to study a unified dark fluid model with a
constant adiabatic sound speed but with the entropic perturbations. When the
entropic perturbations are included, an effective sound speed, which reduces to
the adiabatic sound speed when the entropic perturbations are zero, has to be
specified as an additional free model parameter. Due to the relations between
the adiabatic sound speed and equations of state (EoS)
, the equation of state can be
determined up to an integration constant in principle when an adiabatic sound
speed is given. Then there are two degrees of freedom to describe the linear
perturbations for a fluid. Its micro-scale properties are characterized by its
EoS or adiabatic sound speed and an effective sound speed. We take the
effective sound speed and adiabatic sound speed as free model parameters and
then use the currently available cosmic observational data sets, which include
type Ia supernova Union 2.1, baryon acoustic oscillation and WMAP 7-year data
of cosmic background radiation, to constrain the possible entropic
perturbations and the adiabatic sound speed via the Markov Chain Monte Carlo
method. The results show that the cosmic observations favor a small effective
sound speed in region.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
A New Unified Dark Fluid Model and Its Cosmic Constraint
In this paper, we propose a new unified dark fluid (UDF) model with equation
of state (EoS) , which includes the generalized
Chaplygin gas model (gGg) as its special case, where , and
are three positive numbers. It is clear that this model reduces to the gCg
model with EoS , when ,
and . By combination the cold dark matter
and the cosmological constant, one can coin a EoS of unified dark fluid in the
form of . With this
observations, our proposed EoS provides a possible deviation from CDM
model when the model parameters and deviate from 1 and 3
respectively. By using the currently available cosmic observations from type Ia
supernovae (SN Ia) Union2.1, baryon acoustic oscillation (BAO) and cosmic
microwave background radiation (CMB), we test the viability of this model and
detect the possible devotion from the CDM model. The results show that
the new UDF model fits the cosmic observation as well as that of the
CDM model and no deviation is found from the CDM model in
confidence level. However, our new UDF model can give a non-zero
sound speed, as a contrast, which is zero for the CDM model. We expect
the large structure formation information can distinct the new UDF model from
the CDM model.Comment: 7 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1204.5571, arXiv:1204.479
Constraints on the Holographic Dark Energy Model from Type Ia Supernovae, WMAP7, Baryon Acoustic Oscillation and Redshift-Space Distortion
In this paper, we use the joint measurement of geometry and growth rate from
matter density perturbations to constrain the holographic dark energy model.
The geometry measurement includes type Ia supernovae (SN Ia) Union2.1, full
information of cosmic microwave background (CMB) from WMAP-7yr and baryon
acoustic oscillation (BAO). For the growth rate of matter density
perturbations, the results measured from the redshift-space
distortion (RSD) in the galaxy power spectrum are employed. Via the Markov
Chain Monte Carlo method, we try to constrain the model parameters space. The
jointed constraint shows that and with regions. After marginalizing the other irrelevant
model parameters, we show the evolution of the equation of state of HDE with
respect to the redshift . Though the current cosmic data points favor a
phantom like HDE Universe for the mean values of the model parameters in the
future, it can behave like quintessence in regions.Comment: 10 pages, 4 figures, to appear in Phys. Rev.
Probing the Neutrino Mass through the Cross Correlation between the Rees-Sciama Effect and Weak Lensing
Cosmology plays a fundamental role to determine the neutrino mass, therefore
also to determine its mass hierarchy, since the massive neutrino contributes to
the total matter density in the Universe at the background and perturbation
levels, once it becomes non-relativistic. After the non-relativistic transition
the fluctuations are smashed out at the scales . Therefore, the
missing fluctuation in the total matter is imprinted on the large scale
structure, say the suppression of the matter power spectrum at the scales . In this paper, instead of considering
the linear perturbation theory, which is well understood in the presence of
neutrino, we propose to use the cross correlation between the Rees-Sciama
effect and weak lensing to probe the neutrino mass. At the small scales, the
density contrast grows faster than the background scale factor ,
that makes a sign flipping on , which happens only in the non-linear regime. We show that
the flipping scale in the cross power spectrum between the Rees-Sciama effect
and weak lensing depends on the neutrino mass by assuming the shallow and deep
weak lensing surveys. Our analysis shows that the Deep survey has larger
signal-to-noise ratio . Finally, we use the Fisher information
matrix to forecast constraint on the neutrino mass.Comment: 7 pages, 5 figures, to appear in JCA
Detecting Primordial Gravitational Waves Signal from BICEP2 and {\it Planck} HFI GHz Dust Polarization
The dust polarization is parameterized as a power law form of the multipole
: ( denotes or
), where is its amplitude with the ratio and . Extrapolating to GHz from
GHz yields a value of
(and an additional uncertainty ) over the
range . Based on these data, we report the tensor-to-scalar ratio
defined at by joining the
BICEP2+{\it Planck}2013+WMAP9+BAO+HST and {\it Planck} HFI GHz dust
polarization and its implication to the detection of the primordial
gravitational waves. Considering the CDM+ model, we found
at confidence level with and at
confidence level with . The results imply no
significant evidence for the primordial gravitational waves in
regions. However the post probability distribution of peaks at a small
positive value. And moves to larger positive values when the extrapolation
error bars are included. This might imply a very weak signal of the primordial
gravitational waves. It also implies the crucial fact in calibrating the
amplitude of the dust polarizations in detecting the primordial gravitational
waves in the future. When the running of the scalar spectral tilt is included,
we found at confidence level with and
at confidence level with
. The later one implies the detection of the
primordial gravitational waves in regions at the cost of decreasing
the value of to .Comment: 5 pages, 4 figures, title changed, n_{run} was include
Confronting DGP Braneworld Gravity with Cosmic Observations after Planck Data
The normal branch of Dvali-Gabadadze-Porrati braneworld gravity with brane
tension is confronted by the currently available cosmic observations from the
geometrical and dynamical perspectives. On the geometrical side, the type Ia
supernova as standard candle, the baryon acoustic oscillation as standard ruler
and the cosmic microwave background measurement from the first released 15.5
months data were used to fix the background evolutions. On the dynamical side,
the redshift space distortion data will be used to determine the evolution of
the matter perturbation. Through a Markov chain Monte Carlo analysis, we found
the dimensionless crossover scale
in a spatially
flat normal branch of Dvali-Gabadadze-Porrati braneworld. This result suggests
that the crossover scale should be around which is
consistent with the previous result and greater. It also
implies that the five-dimensional gravity effect is weak to be observed in
scale.Comment: 6 pages, 3 figures, match the published versio
Holographic Dark Energy Model with Hubble Horizon as an IR Cut-off
The main task of this paper is to realize a cosmic observational compatible
universe in the framework of holographic dark energy model when the Hubble
horizon is taken as the role of an IR cut-off. When the model parameter
of a time variable cosmological constant (CC)
becomes time or scale dependent, an extra term enters in the effective equation
of sate (EoS) of the vacuum energy .
This extra term can make the effective EoS of time variable CC cross the
cosmological boundary and be phantom-like at present. For the lack of a first
principle and fundamental physics theory to obtain the form , we give a
simple parameterized form of as an example. Then the model is confronted
by the cosmic observations including SN Ia, BAO and CMB shift parameter .
The result shows that the model is consistent with cosmic observations.Comment: 9 pages, 2 figures, Published Versio
Strong Gravitational Lensing and Its Cosmic Constraints
In this paper, we propose a new method to use the strong lensing data sets to
constrain a cosmological model. By taking the ratio
as cosmic observations, one can {\it completely} eliminate the uncertainty
caused by the relation which
characterizes the relation between the stellar velocity dispersion
and the velocity dispersion . Via our method, a relative tight
constraint to the cosmological model space can be obtained, for the spatially
flat CDM model as an example in regions. And by using this method, one can
also probe the nature of dark energy and the spatial curvature of our Universe
Testing coupled dark energy with large scale structure observation
The coupling between the dark components provides a new approach to mitigate
the coincidence problem of cosmological standard model. In this paper, dark
energy is treated as a fluid with a constant equation of state, whose coupling
with dark matter is . In the frame of dark energy,
we derive the evolution equations for the density and velocity perturbations.
According to the Markov Chain Monte Carlo method, we constrain the model by
currently available cosmic observations which include cosmic microwave
background radiation, baryon acoustic oscillation, type Ia supernovae, and
data points from redshift-space distortion. The results show the
interaction rate in 3 regions:
, which
means that the recently cosmic observations favor a small interaction rate
which is up to the order of , meanwhile, the measurement of
redshift-space distortion could rule out the large interaction rate in the
1 region.Comment: 12 pages, 10 figures. arXiv admin note: text overlap with
arXiv:1401.128
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