arXiv subjects

Lixin Xu

Publications and source records attributed to Lixin Xu.

At least 73 records · Page 4Linked to original sources

arXiv2016

Distinguish three time-dependent dark energy models using statefinder pairs with error bars and Bayesian evidence

In this work, two completely different approaches, statefinder with error bars and Bayesian evidence, are used to distinguish and judge three time-dependent dark energy models. The parameters constrain for the three dark energy models are given using the current cosmic observational data sets : $Planck$ 2015, SNIa, BAO and OHD. Using the statefinder pairs with error bars, we find that the error region of the dark energy model, whose equation of state parameter is given by $w(a) = w_0+w_3\frac{1-a}{a^2+(1-a)^2}$, is relativity compact than the other two models during the all the evolving history. Meanwhile, the Bayesian evidence also provide that this model is significantly better than the other two models and the other two models are inconclusive. Then, there are reasons for believing that this model is a preferential candidate in dark energy investigation rather than the other two.

gr-qc↗

arXiv2016

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 $k\gg k_{fs}$. Therefore, the missing fluctuation in the total matter is imprinted on the large scale structure, say the suppression of the matter power spectrum $ΔP/P\approx -8f_ν$ at the scales $k\gg k_{fs}$. 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 $δ\sim a$, that makes a sign flipping on $Φ' \propto \mathcal{H}δd\ln (δ/a)/d\ln a$, 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 $S/N\sim 160$. Finally, we use the Fisher information matrix to forecast constraint on the neutrino mass.

astro-ph.CO↗

arXiv2016

New constraints on cosmic polarization rotation from the ACTPol cosmic microwave background B-Mode polarization observation and the BICEP2 constraint update

Recently ACTPol has measured the cosmic microwave background (CMB) B-mode and E-mode polarizations and obtained TE, EE, BB, TB and EB power spectra in the multipole range 225-8725. In our previous paper (Ap. J. 792 (2014) 35 [Paper I]), we have analyzed jointly the results of three experiments on the CMB B-mode polarization -- SPTpol, POLARBEAR and BICEP2 to include in the model, in addition to the gravitational lensing and the inflationary gravitational waves components, also the fluctuation effects induced by the cosmic polarization rotation (CPR), if it exists within the upper limits at the time. In this paper, we fit both the mean CPR angle <α> and its fluctuation <δα2> from the new ACTPol data, and update our fitting of CPR fluctuations using BICEP2 data taking the new Planck dust measurement results into consideration. We follow the method of Paper I. The mean CPR angle is constrained from the EB correlation power spectra to |<α>| < 14 mrad (0.8°) and the fluctuation (rms) is constrained from the BB correlation power spectra to <δα2>1/2 < 29.3 mrad (1.68°). Assuming that the polarization angle of Tau A does not change from 89.2 to 146 GHz, the ACTPol data give <α> = 1.0 {\pm} 0.63°. These results suggest that the inclusion of the present ACTPol data is consistent with no CPR detection. With the new Planck dust measurement, we update our fits of the BICEP2 CPR fluctuation constraint to be 32.8 mrad (1.88°). The joint ACTpol-BICEP2-POLARBEAR CPR fluctuation constraint is 23.7 mrad (1.36°).

astro-ph.CO↗

arXiv2016

Thermodynamics of Apparent Horizon and Friedmann Equations in Big Bounce Universe

In this paper, we study a big bounce universe typified by a non-singular big bounce, as opposed to a singular big bang. This cosmological model can describe radiation dominated early universe and matter dominated late universe in FRW model. The connections between thermodynamics and gravity are observed here. In the early stage of both cold and hot universes, we find there is only one geometry containing a 4D de Sitter universe with a general state parameter. We also find the form of the apparent horizon in the early universe strongly depends on the extra dimension, which suggests that the influence of the extra dimension could in principle be found in the early universe. Moreover, we show that in the late stages of both cold and hot universes, the moment when the apparent horizon begins to bounce keeps essentially in step with the behavior of the cosmological scalar factor.

gr-qc↗

arXiv2016

Cosmic Constraints to wCDM Model from Strong Gravitational Lensing

In this paper, we study the cosmic constraint to $w$CDM model via $118$ strong gravitational lensing systems which are complied from SLACS, BELLS, LSD and SL2S surveys, where the ratio between two angular diameter distances $D^{obs} = D_A(z_l,z_s)/D_A(0,z_s)$ is taken as a cosmic observable. To obtain this ratio, we adopt two strong lensing models: one is the singular isothermal sphere model (SIS), the other one is the power-law density profile (PLP) model. Via the Markov Chain Mote Carlo method, the posterior distribution of the cosmological model parameters space is obtained. The results show that the cosmological model parameters are not sensitive to the parameterized forms of the power-law index $γ$. Furthermore, the PLP model gives a relative tighter constraint to the cosmological parameters than that of the SIS model. The predicted value of $Ω_m=0.31^{+0.44}_{-0.24}$ by SIS model is compatible with that obtained by {\it Planck}2015: $Ω_{m}=0.313\pm0.013$. However, the value of $Ω_m=0.15^{+0.13}_{-0.11}$ based on the PLP model is smaller and has $1.25σ$ tension with that obtained by {\it Planck}2015 result. This discrepancy maybe come from the systematic errors.

gr-qc↗

arXiv2015

Galaxy clustering, CMB and supernova data constraints on $ϕ$CDM model with massive neutrinos

We investigate a scalar field dark energy model (i.e., $ϕ$CDM model) with massive neutrinos, where the scalar field possesses an inverse power-law potential, i.e., $V(ϕ)\propto ϕ^{-α}$ ($α>0$). We find that the sum of neutrino masses $Σm_ν$ has significant impacts on the CMB temperature power spectrum and on the matter power spectrum. In addition, the parameter $α$ also has slight impacts on the spectra. A joint sample, including CMB data from Planck 2013 and WMAP9, galaxy clustering data from WiggleZ and BOSS DR11, and JLA compilation of Type Ia supernova observations, is adopted to confine the parameters. Within the context of the $ϕ$CDM model under consideration, the joint sample determines the cosmological parameters to high precision. It turns out that $α<4.995$ at 95% CL for the $ϕ$CDM model. And yet, the $Λ$CDM scenario corresponding to $α= 0$ is not ruled out at 95% CL. Moreover, we get $Σm_ν< 0.262$ eV at 95% CL for the $ϕ$CDM model, while the corresponding one for the $Λ$CDM model is $Σm_ν < 0.293$ eV. The allowed scale of $Σm_ν$ in the $ϕ$CDM model is a bit smaller than that in the $Λ$CDM model. It is consistent with the qualitative analysis, which reveals that the increases of $α$ and $Σm_ν$ both can result in the suppression of the matter power spectrum. As a consequence, when $α$ is larger, in order to avoid suppressing the matter power spectrum too much, the value of $Σm_ν$ should be smaller.

astro-ph.CO↗

arXiv2015

Constraints on the dark matter equation of state with redshift-space distortion

In this paper, we study a model which is composed by the cosmological constant and dark matter with nonzero equation of state parameter, which could be called as $Λ$wDM. In the synchronous gauge, we obtain the perturbation equations of dark matter, and deduce the evolution equations of growth factor about the dark matter and baryons. Based on the Markov Chain Monte Carlo method, we constrain this model by the recently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and $fσ_8(z)$ data points from redshift-space distortion. The results present a tighter constraint on the model than the case without $fσ_8(z)$ data. In 3$σ$ regions, we find the dark matter equation of state parameter $w_{dm}$=$0.000111_{- 0.000701-0.00137-0.00180}^{+0.000688+0.00136+0.00181}$. After an extra model parameter $w_{dm}$ is considered, the difference between the minimum values of $χ^2$ of our model and standard model is $Δχ^2_{min}=0.598$. Although the currently available cosmic observations mildly favor the nonzero dark matter equation of state parameter, no significant deviation from the $Λ$CDM model is found in 1$σ$ region.

astro-ph.CO↗

arXiv2015

FRCAMB: An $f(R)$ Code for Anisotropies in the Microwave Background

An $f(R)$ gravity model is proposed to realize a late time accelerated expansion of our Universe. To test the viability of an $f(R)$ 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 $Λ$CDM or $w$CDM, is assumed. This assumption would be non-proper for a specific $f(R)$ model where the background evolution may be different from a $Λ$CDM cosmology. Therefore the main task for this paper is to present a code to calculate the anisotropies in the microwave background for any $f(R)$ 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 $f(R)$ function, its first two derivative with respect to $R$, i.e. $f_R\equiv df/dR$, $f_{RR}\equiv d^2f/dR^2$ and the reasonable values of the model parameters are inputted properly. As by-products, one can also output the effective equation of state of $f(R)$ model, the evolution of the dimensionless energy densities and other interesting cosmological quantities.

astro-ph.CO↗

arXiv2015

Exploring a new interaction between dark matter and dark energy using the growth rate of structure

We present a phenomenological interaction with a scale factor power law form which leads to the appearance of two kinds of perturbed terms, a scale factor spatial variation along with perturbed Hubble expansion rate. We study both the background and the perturbation evolution within the parametrized post-Friedmann scheme, obtaining that the exchange of energy-momentum can flow from dark energy to dark matter in order to keep dark energy and dark matter densities well defined at all times. We combine several measures of the cosmic microwave background (WMAP9+Planck) data, baryon acoustic oscillation measurements, redshift-space distortion data, JLA sample of supernovae, and Hubble constant for constraining the coupling constant and the exponent provided both parametrized the interaction itself. The joint analysis of ${\rm Planck+WMAP9+BAO}$ ${\rm +RSD+JLA+HST}$ data seems to favor large coupling constant, $ξ_c = 0.34403427_{- 0.18907353}^{+ 0.14430125}$ at 1 $σ$ level, and prefers a power law interaction with a negative exponent, thus $β= -0.50863232_{- 0.40923857}^{+ 0.48424166}$ at 1 $σ$ level. The CMB temperature power spectrum indicates that a large coupling constant produces a shift of the acoustic peaks and affects their amplitudes at lower multipoles. In addition, a larger $β$ exponent generates a shift of the acoustic peaks, pointing a clear deviation with respect to the concordance model. The matter power spectrum are sensitive to the variation of the coupling constant and the $β$ exponent. In this context, the interaction alters the scale of matter and radiation equality and pushes it away from the present era, which in turn generates a shift of the turnover point toward to smaller scale.

astro-ph.CO↗

arXiv2015

Gravitational Waves: A Test for Modified Gravity

In a modified gravity theory, the propagation equation of gravitational waves will be presented in a non-standard way. Therefore this tenor mode perturbation of time-space, as a complement to the scalar mode perturbation, provides a unique character distinguishing modified gravity from general relativity. To avoid the model-dependent issue, in this paper, we propose a parametrised modification to the propagation of gravitational waves. We show the effects on the angular power spectrum of cosmic microwave background radiation due to the parametrised modification and its degeneracy to the tensor mode power spectrum index $n_t$ and its running $α_t$. At last, we report the current status on the detection of modified gravity through the currently available cosmic observations. Our results show no significant deviation to general relativity.

astro-ph.CO↗

arXiv2015

Constraint on $f(R)$ Gravity through the Redshift Space Distortion

In this paper, a specific family of $f(R)$ models that can produce the $Λ$CDM background expansion history is constrained by using the currently available geometric and dynamic probes. The scale dependence of the growth rate $f(z,k)$ in this specific family of $f(R)$ model is shown. Therefore to eliminate the scale dependence of $fσ_8(z)$ in theory, which usually is defined as the product of $f(z,k)$ and $σ_8(z)$, we define $fσ_8(z)=dσ_8(z)/d\ln a$ which is obviously scale independent and reproduces the conventional definition in the standard $Λ$CDM cosmology. In doing so, under the assumption that future probes having the same best fit values as the current ten data points of $fσ_8(z)$, even having $20\%$ error bars enlarged, we find a preliminary constraint $f_{R0}=-2.58_{-0.58}^{+2.14}\times 10^{-6}$ in $1σ$ regions. This indicates the great potential that redshift space distortions have in constraining modified gravity theories. We also discuss the nonlinear matter power spectrum based on different halo fit models.

astro-ph.CO↗

arXiv2015

Reduced modified Chaplygin gas cosmology

In this paper, we study cosmologies containing the reduced modified Chaplygin gas (RMCG) fluid which is reduced from the modified Chaplygin gas $p=Aρ-Bρ^{-α}$ for the value of $α=-1/2$. In this special case, dark cosmological models can be realized for different values of model parameter $A$. We investigate the viabilities of these dark cosmological models by discussing the evolutions of cosmological quantities and using the currently available cosmic observations. It is shown that the special RMCG model ($A=0$ or $A=1$) which unifies the dark matter and dark energy should be abandoned. For $A=1/3$, RMCG which unifies the dark energy and dark radiation is the favorite model according to the objective Akaike information criteria. In the case of $A<0$, RMCG can achieve the features of the dynamical quintessence and phantom models, where the evolution of the universe is not sensitive to the variation of model parameters.

astro-ph.CO↗

arXiv2014

Interacting parametrized post-Friedmann method

We apply the interacting parametrized post-Friedmann (IPPF) method to a coupled dark energy model where the interaction is proportional to dark matter density at background level. In doing so, we perform a Markov Chain Monte-Carlo analysis which combines several cosmological probes including the cosmic microwave background (WMAP9+Planck) data, baryon acoustic oscillation (BAO) measurements, JLA sample of supernovae, Hubble constant (HST), and redshift-space distortion (RSD) measurements through the ${\rm f}σ_{8}{\rm (z)}$ data points. The joint observational analysis of ${\rm Planck+WP+JLA+BAO+HST+RSD}$ data leads to a coupling parameter, $ξ_{c}=0.00140_{-0.00080}^{+0.00079}$ at $1σ$ level for vanishing momentum transfer potential; this value is reduced a when the momentum transfer potential is switched on, giving $ξ_{c}=0.00136_{-0.00073}^{+0.00080}$ at $1σ$ level. The CMB power spectrum shows up a correlation between the coupling parameter $ξ_{c}$ and the position of acoustic peaks or their amplitudes. The first peak's height increases when $ξ_{c}$ takes larger values and its position is shifted. We also obtain the matter power spectrum may be affected by the strength of interaction coupling over scales bigger that $10^{-2} {\rm h~ Mpc^{-1}}$, reducing its amplitude in relation to the vanilla model.

astro-ph.CO↗

arXiv2014

Detecting Primordial Gravitational Waves Signal from BICEP2 and {\it Planck} HFI $353$GHz Dust Polarization

The dust polarization is parameterized as a power law form of the multipole $l$: $D^{XX}_{l}=A^{XX}l(l+1)l^{α_{XX}}/(2π)$ ($XX$ denotes $BB$ or $EE$), where $A^{XX}$ is its amplitude with the ratio $A^{BB}/A^{EE}=0.52\pm 0.02$ and $α_{BB,EE}=-2.42\pm 0.02$. Extrapolating to $150$GHz from $353$GHz yields a value of $D^{BB}_{l=80}=(1.32\pm 0.29)\times 10^{-2}μK^2$ (and an additional uncertainty $(+0.28,-0.24)\times 10^{-2}μK^2$) over the range $40<l<120$. Based on these data, we report the tensor-to-scalar ratio $r=A_{t}/A_{s}$ defined at $k_0=0.05 \text{Mpc} ^{-1}$ by joining the BICEP2+{\it Planck}2013+WMAP9+BAO+HST and {\it Planck} HFI $353$GHz dust polarization and its implication to the detection of the primordial gravitational waves. Considering the $Λ$CDM+$r$ model, we found $r<0.108$ at $95\%$ confidence level with $σ_{stat}=0.29$ and $r<0.129$ at $95\%$ confidence level with $σ_{stat+extr}=0.29+0.28$. The results imply no significant evidence for the primordial gravitational waves in $1σ$ regions. However the post probability distribution of $r$ peaks at a small positive value. And $r$ 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 $r<0.079$ at $95\%$ confidence level with $σ_{stat}=0.29$ and $r=0.091_{-0.069}^{+0.042}$ at $95\%$ confidence level with $σ_{stat+extr}=0.29+0.28$. The later one implies the detection of the primordial gravitational waves in $1σ$ regions at the cost of decreasing the value of $D^{BB}_{l=80}$ to $0.67_{-0.25}^{+0.25}$.

astro-ph.CO↗

arXiv2014

Coupled dark energy with perturbed Hubble expansion rate

The coupling between dark sectors provides a possible 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 proportional the Hubble parameter and energy density of dark energy, that is, $\bar{Q}=3ξ_x\bar{H}\barρ_x$. Particularly, we consider the Hubble expansion rate to be perturbed in the perturbation evolutions of dark sectors. Using jointing data sets which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and redshift-space distortions, we perform a full Monte Carlo Markov Chain likelihood analysis for the coupled model. The results show that the mean value with errors of interaction rate is: $ξ_x=0.00305_{-0.00305-0.00305-0.00305}^{+0.000645+0.00511+0.00854}$ for $Q^μ_A\parallel u^μ_c$; $ξ_x=0.00317_{-0.00317-0.00317-0.00317}^{+0.000628+0.00547+0.00929}$ for $Q^μ_A\parallel u^μ_x$, which means that the recently cosmic observations favored small interaction rate which is up to the order of $10^{-3}$. Moreover, in contrast to the coupled model with unperturbed expansion rate, we find perturbed Hubble expansion rate could bring about negligible impact on the model parameter space.

astro-ph.CO↗

arXiv2014

Observational constraints on variable equation of state parameters of dark matter and dark energy after Planck

In this paper, we study a cosmological model in general relativity within the framework of spatially flat Friedmann-Robertson-Walker space-time filled with ordinary matter (baryonic), radiation, dark matter and dark energy, where the latter two components are described by Chevallier-Polarski-Linder equation of state parameters. We utilize the observational data sets from SNLS3, BAO and Planck+WMAP9+WiggleZ measurements of matter power spectrum to constrain the model parameters. We find that the current observational data offer tight constraints on the equation of state parameter of dark matter. We consider the perturbations and study the behavior of dark matter by observing its effects on CMB and matter power spectra. We find that the current observational data favor the cold dark matter scenario with the cosmological constant type dark energy at the present epoch.

gr-qc↗

arXiv2014

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 $\bar{Q}=3Hξ_x\barρ_x$. 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 $fσ_8(z)$ data points from redshift-space distortion. The results show the interaction rate in 3$σ$ regions: $ξ_x=0.00328_{-0.00328-0.00328-0.00328}^{+0.000736+0.00549+0.00816}$, which means that the recently cosmic observations favor a small interaction rate which is up to the order of $10^{-2}$, meanwhile, the measurement of redshift-space distortion could rule out the large interaction rate in the 1$σ$ region.

astro-ph.CO↗

arXiv2014

Spherical Collapse for Viscous Generalized Chaplygin Gas Model

The nonlinear collapse for viscous generalized Chaplygin gas Model (VGCG) was analyzed in the framework of spherical top-hat collapse. As the VGCG and baryons are essential to form the large scale structure, we focused on their nonlinear collapse in this paper. We discussed the influence of model parameters $α$ and $ζ_{0}$ on the spherical collapse by varying their values and compare with $ΛCDM$. The results show that, for the VGCG model, smaller $ζ_{0}$ and larger $α$ make the structure formation earlier and faster, and the collapse curves of VGCG model is almost distinguished with the $ΛCDM$ model when the model parameter $α$ is less than $10^{-2}$.

astro-ph.CO↗