Recently Background Imaging of Cosmic Extragalactic Polarization （B2） discovered the relic gravitational waves at 7.00- confi- dence level. However, the other cosmic microwave background （CMB） data, for example Pl...Recently Background Imaging of Cosmic Extragalactic Polarization （B2） discovered the relic gravitational waves at 7.00- confi- dence level. However, the other cosmic microwave background （CMB） data, for example Planck data released in 2013 （P13）, prefer a much smaller amplitude of the primordial gravitational waves spectrum if a power-law spectrum of adiabatic scalar perturbations is assumed in the six-parameter ACDM cosmology. In this paper, we explore whether the wCDM model and the running spectral index can relax the tension between B2 and other CMB data. Specifically we found that a positive running of running of spectral index is preferred at 1.70- level from the combination of B2, P 13 and WMAP Polarization data.展开更多
Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe top...Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe topic of the age problem inthe new agegraphic dark energy(NADE)model.We determine the age of the universe in the NADE model by fitting the observational data,including type Ia supernovae(SNIa),baryon acoustic oscillations(BAO)and the cosmic microwave background(CMB).We find that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255.In order to overcome such a difficulty,we consider the possible interaction between dark energy and dark matter.We show that this quasar can be successfully accommodated in the interacting new agegraphic dark energy(INADE)model at the 2σlevel under the current observational constraints.展开更多
Taiji,a space-based gravitational-wave observatory,consists of three satellites forming an equilateral triangle with arm length of 3×10^6 km,orbiting around the Sun.Taiji is able to observe the gravitationalwave ...Taiji,a space-based gravitational-wave observatory,consists of three satellites forming an equilateral triangle with arm length of 3×10^6 km,orbiting around the Sun.Taiji is able to observe the gravitationalwave standard siren events of massive black hole binary(MBHB)merger,which is helpful in probing the expansion of the universe.In this paper,we preliminarily forecast the capability of Taiji for improving cosmological parameter estimation with the gravitational-wave standard siren data.We simulate fiveyear standard siren data based on three fiducial cosmological models and three models of MBHB’s formation and growth.It is found that the standard siren data from Taiji can effectively break the cosmological parameter degeneracies generated by the cosmic microwave background(CMB)anisotropies data,especially for dynamical dark energy models.The constraints on cosmological parameters are significantly improved by the data combination CMB+Taiji,compared to the CMB data alone.Compared to the current optical cosmological observations,Taiji can still provide help in improving the cosmological parameter estimation to some extent.In addition,we consider an ideal scenario to investigate the potential of Taiji on constraining cosmological parameters.We conclude that the standard sirens of MBHB from Taiji will become a powerful cosmological probe in the future.展开更多
Combining the latest Planck, Wilkinson Microwave Anisotropy Probe （WMAP）, and baryon acoustic oscillation （BAO） data, we exploit the recent cosmic microwave background （CMB） B-mode power spectra data released by...Combining the latest Planck, Wilkinson Microwave Anisotropy Probe （WMAP）, and baryon acoustic oscillation （BAO） data, we exploit the recent cosmic microwave background （CMB） B-mode power spectra data released by the BICEP2 collaboration to constrain the cosmological parameters of the ACDM model, especially the primordial power spectra parameters of the scalar and the tensor modes, ns, as, r, nt. We obtain constraints on the parameters for a lensed ACDM model using the Markov Chain -- ＋0,0307 ＋0,0061 ＋0,0105 Monte Carlo （MCMC） technique, the marginalized 68% bounds are r -0.1043 -0.0914, ns -0.9617-0.0061, as =-0.0175-0.0097, nt = 0.5198＋-0.4579. We find that a blue tilt for nt is favored slightly, but it is still well consistent with flat or even red tilt. Our r value is slightly smaller than the one obtained by the BICEP group, in that we permit nt as a free parameter without imposing the single-field slow roll inflation consistency relation. When we impose this relation, then r= 0.2130-0.06096 ＋0.0446. For most other parameters, the best fit values and measurement errors are not altered significantly by the introduction of the BICEP2 data.展开更多
Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current...Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current research in theoretical cosmology.In this article,I will describe some signatures of non-linear perturbation theory that do not exist at linear order,focusing on vorticity generation at second order.In doing so,we discuss why this,among other features such as induced gravitational waves and non-Gaussianities,shows that cosmological perturbation theory is crucial for testing models of the universe.展开更多
With the dark energy phenomena explored over a decade, in this present work we discuss a specific case of the generalized Einstein-aether theories, in which the modified Friedmann equation is similar to that in the Dv...With the dark energy phenomena explored over a decade, in this present work we discuss a specific case of the generalized Einstein-aether theories, in which the modified Friedmann equation is similar to that in the Dvali- Gabadadze-Porrati （DGP） brahe world model. We compute the joint statistic constraints on model parameters in this specific case by using the recent type Ia supernovae （SNe Ia） data, the cosmic microwave background （CMB） shift parameter data, and the baryonic acoustic oscillations （BAOs） data traced by the S1oan Digital Sky Survey （SDSS）. Furthermore, we analyze other constrains from the observational Hubble parameter data （OHD）. The comparison with the standard cosmological model （cosmological constant A cold dark matter （ACDM） model） is dearly shown; also we comment on the interesting relation between the coupling constant M in this model and the special accelerate scale in the modified Newtonian dynamies （MOND） model initially given by Milgrom with the hope for interpreting the galaxy rotation curves without introducing mysterious dark matter.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10821504, 11322545, 11335012, 11173021 and 11322324)the Project of KIP of the Chinese Academy of Sciences and the National Basic Research Program of China (Grant No. 2012CB821804)
文摘Recently Background Imaging of Cosmic Extragalactic Polarization （B2） discovered the relic gravitational waves at 7.00- confi- dence level. However, the other cosmic microwave background （CMB） data, for example Planck data released in 2013 （P13）, prefer a much smaller amplitude of the primordial gravitational waves spectrum if a power-law spectrum of adiabatic scalar perturbations is assumed in the six-parameter ACDM cosmology. In this paper, we explore whether the wCDM model and the running spectral index can relax the tension between B2 and other CMB data. Specifically we found that a positive running of running of spectral index is preferred at 1.70- level from the combination of B2, P 13 and WMAP Polarization data.
基金supported by the National Natural Science Foundation of China(Grant Nos.10705041 and 10975032)the National Ministry of Education of China under the innovation program for undergraduate students
文摘Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe topic of the age problem inthe new agegraphic dark energy(NADE)model.We determine the age of the universe in the NADE model by fitting the observational data,including type Ia supernovae(SNIa),baryon acoustic oscillations(BAO)and the cosmic microwave background(CMB).We find that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255.In order to overcome such a difficulty,we consider the possible interaction between dark energy and dark matter.We show that this quasar can be successfully accommodated in the interacting new agegraphic dark energy(INADE)model at the 2σlevel under the current observational constraints.
基金the National Natural Science Foundation of China(11975072,11690021,11875102,and 11835009)the National Program for Support of Top-Notch Young Professionals+1 种基金the Liaoning Revitalization Talents Program(XLYC1905011)the Fundamental Research Funds for the Central Universities(N2005030)。
文摘Taiji,a space-based gravitational-wave observatory,consists of three satellites forming an equilateral triangle with arm length of 3×10^6 km,orbiting around the Sun.Taiji is able to observe the gravitationalwave standard siren events of massive black hole binary(MBHB)merger,which is helpful in probing the expansion of the universe.In this paper,we preliminarily forecast the capability of Taiji for improving cosmological parameter estimation with the gravitational-wave standard siren data.We simulate fiveyear standard siren data based on three fiducial cosmological models and three models of MBHB’s formation and growth.It is found that the standard siren data from Taiji can effectively break the cosmological parameter degeneracies generated by the cosmic microwave background(CMB)anisotropies data,especially for dynamical dark energy models.The constraints on cosmological parameters are significantly improved by the data combination CMB+Taiji,compared to the CMB data alone.Compared to the current optical cosmological observations,Taiji can still provide help in improving the cosmological parameter estimation to some extent.In addition,we consider an ideal scenario to investigate the potential of Taiji on constraining cosmological parameters.We conclude that the standard sirens of MBHB from Taiji will become a powerful cosmological probe in the future.
基金supported by the Chinese Academy of Science Strategic Priority Research Program "The Emergence of Cosmological Structures" (Grant No. XDB09000000)the National Natural Science Foundation of China (Grant Nos. 11103027, 11373030 and 11373031)the National High Technology Research and Development Program of China (Grant No. 2012AA121701)
文摘Combining the latest Planck, Wilkinson Microwave Anisotropy Probe （WMAP）, and baryon acoustic oscillation （BAO） data, we exploit the recent cosmic microwave background （CMB） B-mode power spectra data released by the BICEP2 collaboration to constrain the cosmological parameters of the ACDM model, especially the primordial power spectra parameters of the scalar and the tensor modes, ns, as, r, nt. We obtain constraints on the parameters for a lensed ACDM model using the Markov Chain -- ＋0,0307 ＋0,0061 ＋0,0105 Monte Carlo （MCMC） technique, the marginalized 68% bounds are r -0.1043 -0.0914, ns -0.9617-0.0061, as =-0.0175-0.0097, nt = 0.5198＋-0.4579. We find that a blue tilt for nt is favored slightly, but it is still well consistent with flat or even red tilt. Our r value is slightly smaller than the one obtained by the BICEP group, in that we permit nt as a free parameter without imposing the single-field slow roll inflation consistency relation. When we impose this relation, then r= 0.2130-0.06096 ＋0.0446. For most other parameters, the best fit values and measurement errors are not altered significantly by the introduction of the BICEP2 data.
文摘Cosmological perturbation theory is a key tool to study the universe.The linear or first order theory is well understood,however,developing and applying the theory beyond linear order is at the cutting edge of current research in theoretical cosmology.In this article,I will describe some signatures of non-linear perturbation theory that do not exist at linear order,focusing on vorticity generation at second order.In doing so,we discuss why this,among other features such as induced gravitational waves and non-Gaussianities,shows that cosmological perturbation theory is crucial for testing models of the universe.
基金Supported by Natural Science Foundation of China under Grant Nos. 11075078 and 10675062by the project of knowledge Innovation Program (PKIP) of Chinese Academy of Sciences (CAS) under Grant No. KJCX2.YW.W10 through the KITPC astrophysics and cosmology programmes where we have initiated this present work
文摘With the dark energy phenomena explored over a decade, in this present work we discuss a specific case of the generalized Einstein-aether theories, in which the modified Friedmann equation is similar to that in the Dvali- Gabadadze-Porrati （DGP） brahe world model. We compute the joint statistic constraints on model parameters in this specific case by using the recent type Ia supernovae （SNe Ia） data, the cosmic microwave background （CMB） shift parameter data, and the baryonic acoustic oscillations （BAOs） data traced by the S1oan Digital Sky Survey （SDSS）. Furthermore, we analyze other constrains from the observational Hubble parameter data （OHD）. The comparison with the standard cosmological model （cosmological constant A cold dark matter （ACDM） model） is dearly shown; also we comment on the interesting relation between the coupling constant M in this model and the special accelerate scale in the modified Newtonian dynamies （MOND） model initially given by Milgrom with the hope for interpreting the galaxy rotation curves without introducing mysterious dark matter.
