Some Studies On Observational Test Of Dark Energy

Since its discovery,cosmic acceleration has become one of the biggest puzzles in modern cosmology.If general gravity is correct on all scales in our cosmology,we need to introduce "dark energy" to explain cosmic acceleration.Current cosmological obser-vations,such as the type la supernovae(SN),the cosmic microwave background(CMB),the baryon acoustic oscillation(BAO),and the direct measurement of Hubble constant H0,have led to the precision cosmology,in which the geometry and matter/energy con-tents of the universe are precisely determined.However,the nature of dark energy still remains enigmatic.It is of great importance to combine different,observations to precisely determine the equation of state of dark energy.In this thesis,we study the observational test of dark energy in the following three aspects:(?)as an important supplement to current popular cosmological observations,the effect of future redshift drift measurement on dark energy constraints;(?)the control of the systematic uncertainties of current type la supernovae observation;(?)aside from the parameters of standard ACDM model,more important parameters to be considered,such as equation of state of dark energy ?,the tensor-to-scalar ratio r and parameters of neutrino mass.In the analysis,we constrain the dark energy models using combined cosmological observations.The redshift drift measurement,i.e.the Sandage-Loeb(SL)test signal,directly mea-sures the expansion of the universe,by detecting redshift drift in the spectra of Lyman-?forest of distant quasars.This method covers the "redshift desert" of 2(?)z(?)5,and thus will definitely provide an important supplement to other probes in cosmological con-straints.In this paper,we quantify the ability of SL test signal by a CODEX-like spec-trograph for constraining dark energy models,including ACDM,?CDM,and ?0?aCDM models,four typical interacting dark energy models,as well as two typical f(T)models.To avoid the potential inconsistency with other observational data,we take the best-fitting dark energy models constrained by the current observations as the fiducial models to produce 30 mock SL test data.We quantify the constraining power of the SL test in the current geometric constraints and in the future high-precision joint geometric constraints on dark energy,respectively.The results show that the redshift drift measurement is extremely helpful in breaking the existing parameter degeneracies,and thus is a necessary supplement to other probes.The strong degeneracy between the present-day matter density ?m and Hubble constant H0 in all considered models is well broken by the SL test.Thus the precision of ?m and H0 can be greatly improved.However,the constraints on equation of state ?,the interacting item ?,and the model parameters of f(T)models are only slightly influenced.Furthermore,in the future geometric constraints,the redshift drift observations would help break the geometric degeneracies in a meaningful way,thus the measurement preci-sions of Qm,?m,H0,?,and ? could also be substantially improved using future probes.We conclude that the improvement of constraint precision by SL test data is independent of the cosmological models in the background.It is very significant to include SL test data in future cosmological constraints.Previous studies have shown that,there is strong evidence for the redshift-evolution of color-luminosity parameter ? of type la supernova.This possibly be one of the most important factors that can lead to systematic uncertainties of type la supernova.In this paper,we explore the effects of varying ? on the cosmological constraints of holographic dark energy model,?CDM model and its three interacting extensions.The results show that for all considered models,? deviates from a constant at high confidence level.Varying?can significantly change the fitting results of various cosmological parameters.Relative to the differences between the constant ? and varying ? cases,the effects of different light-curve fitters on parameter estimation are very small.Our work indicates that the evolution of ? is insensitive to the interaction between dark sectors.We conclude that the effects of constraint precision by varying ? is independent of the cosmological models in the background.Therefore,the evolution of ? should be taken into account seriously in the cosmological fits.The detection of the B-mode polarization of CMB by the BICEP2 experiment in 2014 implies that the tensor-to-scalar ratio r should be involved in the base standard cosmology.Meanwhile,discovery of neutrino oscillations has indicated that neutri-nos have nonzero masses.It is of great importance to measure the absolute masses of neutrinos,using different cosmological experiments.In this paper,we extend the ACDM+r+neutrino/dark radiation models by replacing the cosmological constant with the dynamical dark energy with constant w.We focus on the constraints on the to-tal mass of active neutrinos,?mv,the effective number of relativistic species,Neff,and the mass of sterile neutrinos,mv,sterile eff.Four neutrino plus dark energy model-s are considered,i.e.,the ?CDM+r+?mv,?CDM+r+Neff,?CDM+r+?mv+Neff,and ?CDM+r+Neff+mv,sterile eff models.The current observational data considered in this paper include Planck+WP,BAO,H0,Planck SZ cluster,Planck CMB lensing,cosmic shear,and BICEP2 data.We first test the data consistency in the four cosmological models.For the ?CDM+r+?mv model,the CMB+BAO data are basically consistent with other observations(except for BICEP2).For the ?CDM+r+Neff model,the consideration of ? still could not well relieve the tension between Planck and clusters or BICEP2.Both the ?CDM-r+?mv+Neff model and the ?CDM+r+Neff+mv,sterile eff model are successful in relieving the tensions be-tween Planck and other astrophysical observations.However,in the ?CDM+r+?mv+Neff model,one has to assume that the massive active neutrinos coexist with dark radiation,and thus we believe that the sterile neutrino model is more natural.Then we combine the consistent data sets to perform joint constraints on the models.We focus on the constraints on the parameters ?,?mv,Neff,and mv,sterile.eff· The results show that the neutrino mass plays a more important role thanNeff in the fits.