arXiv subjects

Jun-Qing Xia

Publications and source records attributed to Jun-Qing Xia.

At least 109 records · Page 6Linked to original sources

arXiv2008

Probing for cosmological parameters with LAMOST measurement

In this paper we study the sensitivity of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project to the determination of cosmological parameters, employing the Monte Carlo Markov Chains (MCMC) method. For comparison, we first analyze the constraints on cosmological parameters from current observational data, including WMAP, SDSS and SN Ia. We then simulate the 3D matter power spectrum data expected from LAMOST, together with the simulated CMB data for PLANCK and the SN Ia from 5-year Supernovae Legacy Survey (SNLS). With the simulated data, we investigate the future improvement on cosmological parameter constraints, emphasizing the role of LAMOST. Our results show the potential of LAMOST in probing for the cosmological parameters, especially in constraining the equation-of-state (EoS) of the dark energy and the neutrino mass.

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arXiv2008

Determining Cosmological Parameters with Latest Observational Data

In this paper, we combine the latest observational data, including the WMAP five-year data (WMAP5), BOOMERanG, CBI, VSA, ACBAR, as well as the Baryon Acoustic Oscillations (BAO) and Type Ia Supernoave (SN) "Union" compilation (307 sample) to determine the cosmological parameters. Our results show that the $Λ$CDM model remains a good fit to the current data. In a flat universe, we obtain the tight limit on the constant EoS of dark energy as, $w=-0.977\pm0.056$ ($1 σ$). For the dynamical dark energy models with time evolving EoS, we find that the best-fit values are $w_0=-1.08$ and $w_1=0.368$, implying the preference of Quintom model whose EoS gets across the cosmological constant boundary. For the curvature of universe, our results give $-0.012<Ω_k<0.009$ (95% C.L.) when fixing $w_{\DE}=-1$. When considering the dynamics of dark energy, the flat universe is still a good fit to the current data. Regarding the neutrino mass limit, we obtain the upper limits, $\sum m_ν<0.533$ eV (95% C.L.) within the framework of the flat $Λ$CDM model. When adding the SDSS Lyman-$α$ forest power spectrum data, the constraint on $\sum m_ν$ can be significantly improved, $\sum m_ν<0.161$ eV (95% C.L.). Assuming that the primordial fluctuations are adiabatic with a power law spectrum, within the $Λ$CDM model, we find that the upper limit on the ratio of the tensor to scalar is $r<0.200$ (95% C.L.) and the inflationary models with the slope $n_s\geq1$ are excluded at more than $2 σ$ confidence level. However, in the framework of dynamical dark energy models, the allowed region in the parameter space of ($n_s$,$r$) is enlarged significantly. Finally, we find no evidence for the large running of the spectral index. (Abridged)

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arXiv2008

On using the WMAP distance priors in constraining the time evolving equation of state of dark energy

Recently, the WMAP group has published their five-year data and considered the constraints on the time evolving equation of state of dark energy for the first time from the WMAP distance information. In this paper, we study the effectiveness of the usage of these distance information and find that these compressed CMB information can give similar constraints on dark energy parameters compared with the full CMB power spectrum if dark energy perturbations are included, however, once incorrectly neglecting the dark energy perturbations, the difference of the results are sizable.

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arXiv2008

A Model Of Inflationary Cosmology Without Singularity

In this letter, we propose a model of inflationary cosmology with a bounce preceded and study its primordial curvature perturbations. Our model gives rise to a primordial power spectrum with a feature of oscillation on large scales compared with the nearly scale-invariant spectrum generated by the traditional slow rolling inflation model. We will show this effect changes the Cosmic Microwave Background (CMB) temperature power spectrum and the Large Scale Structure (LSS) matter power spectrum. And further with a detailed simulation we will point out this signal is detectable to the forthcoming observations, such as PLANCK and LAMOST.

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arXiv2008

Testing CPT Symmetry with CMB Measurements: Update after WMAP5

In this Letter we update our previous result on the test of CPT symmetry with Cosmic Microwave Background (CMB) measurements. A CPT violating interaction in the photon sector ${\cal L}_{cs} \sim p_μA_ν\tilde F^{μν}$ gives rise to a rotation of the polarization vectors of the propagating CMB photons. Recently the WMAP group used the newly released polarization data of WMAP5 to measure this rotation angle $Δα$ and obtained $Δα=-1.7\pm2.1$ deg ($1σ$). However, in their analysis the BOOMERanG 2003 data is not included. Here we revisit this issue by combining the full data of WMAP5 and BOOMERanG 2003 angular power spectra for the measurement of this rotation angle $Δα$ and find that $Δα=-2.6\pm1.9$ deg at a 68% confidence level.

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arXiv2008

Testing CPT Symmetry with CMB Measurements

In this paper we study the possibility of testing \emph{CPT} symmetry with Cosmic Microwave Background (CMB) measurements. Working with an effective lagrangian of the photon with \emph{CPT} violation ${\cal L} \sim p_μA_ν\tilde F^{μν}$ which causes the polarization vectors of the propagating CMB photons rotated, we determine the rotation angle $Δα$ using the BOOMERanG 2003 and the WMAP3 angular power spectra. In this analysis we have included the newly released $TC$ and $GC$ ($l<450$) information of WMAP3 and found $Δα=-6.2\pm3.8$ deg at $1σ$ confidence level. This result increases slightly the significance for the \emph{CPT} violation obtained in our previous paper (Feng \emph{et al.}, 2006) $Δα=-6.0 \pm 4.0$ deg (1$σ$). Furthermore we examine the constraint on the rotation angle with the simulated Planck data. Our results show that the Planck will be sensitive to $Δα$ at the level of 0.057 deg and able to test the \emph{CPT} symmetry with a higher precision.

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arXiv2008

Constraining Slow-Roll Inflation in the Presence of Dynamical Dark Energy

In this paper we perform a global analysis of the constraints on the inflationary parameters in the presence of dynamical dark energy models from the current observations, including the three-year Wilkinson Microwave Anisotropy Probe (WMAP3) data, Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG, 2dFGRS and ESSENCE (192 sample). We use the analytic description of the inflationary power spectra in terms of the Horizon-flow parameters $\{ε_i\}$. With the first order approximation in the slow-roll expansion, we find that the constraints on the Horizon-flow parameters are $ε_1<0.014 (95% C.L.)$ and $ε_2=0.034\pm0.024 (1σ)$ in the $Λ$CDM model. In the framework of dynamical dark energy models, the constraints become obviously weak, $ε_1<0.022 (95% C.L.)$ and $ε_2=-0.006\pm0.039 (1σ)$, and the inflation models with a "blue" tilt, which are excluded about $2σ$ in the $Λ$CDM model, are allowed now. With the second order approximation, the constraints on the Horizon-flow parameters are significantly relaxed further. If considering the non-zero $ε_3$, the large running of the scalar spectral index is found for the $Λ$CDM model, as well as the dynamical dark energy models.

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arXiv2008

Overcoming the Circular Problem for γ-ray Bursts in Cosmological Global Fitting Analysis

Due to the lack of low redshift long Gamma-Ray Bursts (GRBs), the circular problem has been a severe obstacle for using GRBs as cosmological candles. In this paper, we present a new method to deal with such a problem in MCMC global fitting analysis. Assuming that a certain type of correlations between different observables exists in a subsample of GRBs, for the parameters involved in the correlation relation, we treat them as free parameters and determine them simultaneously with cosmological parameters through MCMC analysis on GRB data together with other observational data. Then the circular problem is naturally eliminated in this procedure. We take the Ghirlanda relation as an example while keeping in mind the debate about its physical validity. Together with SNe Ia, WMAP and SDSS data, we include 27 GRBs with the reported Ghirlanda relation in our study, and perform MCMC global fitting. We consider the $Λ$CDM model and dynamical dark energy models. In each case, in addition to the constraints on the relevant cosmological parameters, we obtain the best fit values as well as the distributions of the correlation parameters $A$ and $C$. We find that the observational data sets other than GRBs can affect $A$ and $C$ considerably through their degeneracies with the cosmological parameters. The results on $A$ and $C$ for different cosmological models are in well agreement within $1σ$ range. The best fit value of $A$ in all models being analyzed is $A\sim 1.53$ with $σ\sim 0.08$. For $C$, we have the best value in the range of $0.94-0.98$ with $σ\sim 0.1$. It is also noted that the distributions of $A$ and $C$ are generally broader than the priors used in many studies in literature. (Abriged)

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arXiv2008

Constraints on the Sound Speed of Dynamical Dark Energy

In this paper we study the sound speed - $c_s^2$, which is directly related to the classical perturbations - of the dynamical dark energy (DE), especially with an equation of state crossing the cosmological constant boundary in details and show its implications on Cosmic Microwave Background (CMB) Anisotropy. With the present observational data of CMB, Type Ia Supernova (SNIa) and galaxy clustering, we perform a global analysis to constrain the sound speed of dark energy, using the Markov Chain Monte Carlo method. We find that the sound speed of dark energy is weakly constrained by current observations thus the futuristic precision measurements of CMB on a very large angular scale (low multipoles) are necessary.

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arXiv2008

Probing for the Cosmological Parameters with PLANCK Measurement

We investigate the constraints on cosmological parameters especially for EoS of dark energy, inflationary parameters, neutrino mass and curvature of universe using simulated Planck data. Firstly we determine cosmological parameters with current observations including ESSENCE, WMAP3, Boomerang-2K2, CBI, VSA, ACBAR, SDSS LRG and 2dFGRS, and take best-fit model as the fiducial model in simulations. In simulations we pay attention to the effects of dynamical dark energy in determination of cosmological parameters. We add simulated SNAP data to do all the simulations. Using present data, we find Quintom dark energy model is mildly favored while \LambdaCDM remains a good fit. In the framework of dynamical dark energy, the constraints on inflationary parameters, m_ν and Ω_{K} become weak compared with the constraints in \LambdaCDM. Intriguingly, we find that the inflationary models with a "blue" tilt, which are excluded about 2σin \LambdaCDM model, are well within 2σregion with the presence of the dynamics of dark energy. The upper limits of neutrino mass are weakened by a factor of 2 (95% C.L.), say, m_ν<1.59 eV and m_ν<1.53 eV for two forms of parametrization of the equation of state of dark energy. The flat universe is a good fit to the current data, namely, |Ω_{K}|<0.03 (95% C.L.). With the simulated Planck and SNAP data, dynamical dark energy and \LambdaCDM might be distinguished at 4σ. And uncertainties of inflationary parameters, m_ν and Ω_{K} can be reduced obviously. We also constrain the rotation angle Δα, denoting possible cosmological CPT violation, with simulated Planck and CMBpol data and find that our results are much more stringent than current constraint and will verify cosmological CPT symmetry with a higher precision. (Abridged)

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arXiv2007

Cosmological CPT Violation, Baryon/Leptogenesis and CMB Polarization

In this paper we study the cosmological CPT-violation and its implications in baryo/leptogenesis and CMB polarization. We propose specifically a variant of the models of gravitational leptogenesis. By performing a global analysis with the Markov Chain Monte Carlo (MCMC) method, we find the current CMB polarization observations from the three-year WMAP (WMAP3) and the 2003 flight of BOOMERANG (B03) data provide a weak evidence for our model. However to verify and especially exclude this type of mechanism for baryo/leptogenesis with cosmological CPT-violation, the future measurements on CMB polarization from PLANCK and CMBpol are necessary.

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arXiv2007

Probing for variation of neutrino mass with current observations

With the latest astronomical data including Cosmic Microwave Background (WMAP three year, CBI, ACBAR, VSA), Type Ia Supernova ("gold sample"), Galaxy Clustering (SDSS 3-D matter power, Lyman-$α$ forest and Baryon Acoustic Oscillating (BAO)), we make a global fitting to constrain the mass varying neutrinos. We find that the parameter $δ$, denoting time evolving of neutrino mass, is weakly constrained and the neutrino mass limit today can be relaxed at least by a factor of two. Adding data of $0\nu2β$ decay of Heidelberg-Moscow experiment to our analysis, we find that $δ$ can be constrained tightly and mass varying neutrinos are favored at about 99.7% confidence level.

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arXiv2007

Cosmological neutrino mass limit and the dynamics of dark energy

We investigate the correlation between the neutrino mass limit and dark energy with time evolving equation of state. Parameterizing dark energy as w=w_0+w_1*z/(1+z), we make a global fit using Markov Chain Monte Carlo technique to determine w_0, w_1, neutrino mass as well as other cosmological parameters simultaneously. We pay particular attention to the correlation between neutrino mass Σm_ν and w_1 using current cosmological observations as well as the future simulated datasets such as PLANCK, SNAP and LAMOST.

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arXiv2006

Probing for dynamics of dark energy and curvature of universe with latest cosmological observations

We use the newly released 182 Type Ia supernova data combined with the third-year Wilkinson Microwave Anisotropic Probe data (WMAP3) and large scale structure (LSS) information including SDSS and 2dFGRS to constrain the dark energy equation of state (EoS) as well as the curvature of universe $Ω_K$. Using the full dataset of Cosmic Microwave Background (CMB) and LSS rather than the shift parameter and linear growth factor, we make a Markov Chain Monte Carlo (MCMC) global fit, while paying particular attention to the dark energy perturbation. Parameterizing the EoS as $w_{DE}(a) = w_{0} + w_{1}(1-a)$, we find the best fit of ($w_0,w_1$) is ($-1.053,0.944$) and for $w_{DE}(a) = w_{0} + w_{1}\sin({3/2}π\ln(a))$, the best fit for ($w_0,w_1$) is ($-1.614,-1.046$). We find that a flat universe is a good approximation, namely, $|Ω_K|>0.06$ has been excluded by 2$σ$ yet the inclusion of $Ω_K$ can affect the measurement of DE parameters owing to their correlation and the present systematic effects of SNIa measurements.

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arXiv2006

Weighing neutrinos in the presence of a running primordial spectral index

The three-year WMAP(WMAP3), combined with other cosmological observations from galaxy clustering and Type Ia Supernova (SNIa), prefers a non-vanishing running of the primordial spectral index independent of the low CMB multipoles. Motivated by this feature we study cosmological constraint on the neutrino mass, which severely depends on what prior we adopt for the spectral shape of primordial fluctuations, taking possible running into account. As a result we find a more stringent constraint on the sum of the three neutrino masses, m_ν< 0.76eV (2 σ), compared with m_ν< 0.90eV (2 σ) for the case where power-law prior is adopted to the primordial spectral shape.

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arXiv2006

Features in Dark Energy Equation of State and Modulations in the Hubble Diagram

We probe the time dependence of the dark energy equation of state (EOS) in light of three-year WMAP (WMAP3) and the combination with other tentative cosmological observations from galaxy clustering (SDSS) and Type Ia Supernova (SNIa). We mainly focus on cases where the EOS is oscillating or with local bumps. By performing a global analysis with the Markov Chain Monte Carlo (MCMC) method, we find the current observations, in particular the WMAP3 + SDSS data combination, allow large oscillations of the EOS which can leave oscillating features on the (residual) Hubble diagram, and such oscillations are potentially detectable by future observations like SNAP, or even by the CURRENTLY ONGOING SNIa observations. Local bumps of dark energy EOS can also leave imprints on CMB, LSS and SNIa. In cases where the bumps take place at low redshifts and the effective EOS are close to -1, CMB and LSS observations cannot give constraints on such possibilities. However, geometrical observations like (future) SNIa can possibly detect such features. On the other hand when the local bumps take place at higher redshifts beyond the detectability of SNIa, future precise observations like Gamma-ray bursts, CMB and LSS may possibly detect such features. In particular, we find that bump-like dark energy EOS on high redshifts might be responsible for the features of WMAP on ranges l \sim 30-50, which is interesting and deserves addressing further.

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arXiv2006

Probing Inflation and Dark Energy with Current Cosmological Observations

It is commonly believed that our Universe has experienced two different stages of accelerated expansion. The early stage is known as inflation and the current acceleration is driven by dark energy. Observing inflation and dark energy dynamics are among the most important aspects of the current cosmological research. In this paper we make a first detailed probe of possible degeneracies between dynamical inflation and dark energy in light of current cosmological observations. We find the inclusion of inflation and dark energy parameters together make the parameter spaces broader, but interestingly deviation from scale-invariant primordial spectrum is sightly more favored by current cosmological observations when one marginalizes over dynamical dark energy models.

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arXiv2006

Scale dependence of the primordial spectrum from combining the three-year WMAP, Galaxy Clustering, Supernovae, and Lyman-alpha forests

We probe the scale dependence of the primordial spectrum in the light of the three-year WMAP (WMAP3) alone and WMAP3 in combination with the other cosmological observations such as galaxy clustering and Type Ia Supernova (SNIa). We pay particular attention to the combination with the Lyman $α$ (Ly$α$) forest. Different from the first-year WMAP (WMAP1), WMAP3's preference on the running of the scalar spectral index on the large scales is now fairly independent of the low CMB multipoles $\ell$. A combination with the galaxy power spectrum from the Sloan Digital Sky Survey (SDSS) prefers a negative running to larger than 2$σ$, regardless the presence of low $\ell$ CMB ($2\le \ell \le 23$) or not. On the other hand if we focus on the Power Law $Λ$CDM cosmology with only six parameters (matter density $Ω_m h^2$, baryon density $Ω_b h^2$, Hubble Constant $H_0$, optical depth $τ$, the spectral index, $n_s$, and the amplitude, $A_s$, of the scalar perturbation spectrum) when we drop the low $\ell$ CMB contributions WMAP3 is consistent with the Harrison-Zel'dovich-Peebles scale-invariant spectrum ($n_s=1$ and no tensor contributions) at $\sim 1σ$. When assuming a simple power law primordial spectral index or a constant running, in case one drops the low $\ell$ contributions ($2\le \ell \le 23$) WMAP3 is consistent with the other observations better, such as the inferred value of $σ_8$. We also find, using a spectral shape with a minimal extension of the running spectral index model, LUQAS$+$ CROFT Ly$α$ and SDSS Ly$α$ exhibit somewhat different preference on the spectral shape.

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