Constraining Dark Energy With Hubble Parameter Measurements

Since two observation teams found that the universe is currently undergoing an accelerating expansion,cosmologists have studied its origin in depth.In order to explain it,there are two popular arguments:dark energy and modified gravity.So far,whether dark energy or modified gravity hasn't been totally accepted by the public.Therefore people established all kinds of cosmological models based on them.In addition,with the development of technology in astronomy,many astronomical observations,including type Ia supernova,cosmic microwave background radiation,baryon acoustic oscillations,Hubble constant H0 and others,also provide a number of important information for our research.Therefore that combining different kinds of observations constrains dark energy is our major method to study the cosmic acceleration.In the thesis,we study the observational test of dark energy in the following two as-pects.Firstly we analyze the effect of future redshift drift measurement on f(T)model.Redshift-drift observation is an important supplement to current cosmological observa-tions because it measures the redshift drift in the Lyman-? forest in the spectra of distant quasars,covering the "redshift desert" of 2(?)z(?)5.To avoid data inconsistency,we use the best-fit models based on current combined observational data as fiducial models to simulate 30 mock data.We quantify the impact of these data on parameter estimation for f(T)gravity theories.Two typical f(T)models are considered,the power-law model f(T)PL and the exponential-form model f(T)EXP.The results show that Redshift-drift observation can effectively break the existing strong degeneracy between the present-day matter density ?m and the Hubble constant H0 in other cosmological observations.For the considered f(T)models,a 30-year observation of redshift drift can improve the con-straint precision of ?m and H0 enormously but cannot effectively improve the constraint precision of the model parameters.Otherwise,in recent years we have done lots of research about Hubble parameter measurements.As is known to us,the usual observables are the luminosity distances or the angular diameter distances,which measure the distance-redshift relation.Actually,the property of dark energy affects the distances(and the growth factor)by a further integration over functions of H(z).Thus the direct measurements of the Hubble param-eter H(z)at different redshifts are of great importance for constraining the properties of dark energy.In this thesis,we show how the typical dark energy models,for example,the ACDM,wCDM,CPL,and holographic dark energy models,can be constrained by the current direct measurements of H(z)(31 data used in total in this paper,covering the redshift range of z ?[0.07,2.34]).In fact,the future redshift-drift observations(also referred to as the Sandage-Loeb test)can also directly measure H(z)at higher redshifts,covering the range of ?[2,5].We thus discuss what role the redshift-drift observations can play in constraining dark energy with the Hubble parameter measurements.We show that the constraints on dark energy can be improved greatly with the H(z)data from only a 10-year observation of redshift drift.