Improving Cosmological Parameter Estimation With The Future Gravitational-wave Observation

The current various cosmological observations are agree with cosmological constant model(ACDM),but it is unbelievable that ?CDM as a 6 parameters models reproduce the evolution of cosmology,including the expansion history and the large-scale structure formation.Moreover,there are still some problems that have not been solved in ?CDM,such as the tension about Hubble constant H0 and the parameter degeneracies existing in the current observations.All these questions mean there are boundedness in the cosmological models and the cosmological observations.So the models and the observations need be further extended.The gravit,ational wave(GW)standard siren as a new cosmological probe can be the extension of current observations.GW from the compact binary stars carry the luminosity distance of the wave source,and with the redshift information detected,we can build distance-redshift relation to limit the dark energy model.Compared with other observations,GW have some advantages:the absolute luminosity distance from compact binary stars is self-calibration and is dependent on the cosmic distance ladder,and that mean the distance error is relatively small;GW can provide the higher redshift information and is helpful for fill the gap in current,observations.Therefore,GW as a cross-check and supplement to current observations maybe is able to improve the estimation of cosmological parameters.In this work,we will investigate how the future gravitational-wave standard siren observations would break the parameter degeneracies existing in the conventional optical observations and how they help improve the parameter estimation in cosmology in two models,including ?CDM and the simplest dynamic dark energy model wCDM.The optical observation include cosmic microwave background radiation,baryon Acoustic Oscillations and type Ia supernovae.Due to the lack of GW events,we make an analysis by the simulated GW data.We take the third-generation ground-based gravitational-wave detector,the Einstein Telescope,as an example,and simulate 1000 events data in the redshift range between 0 and 5 based on the ten-year observation.with the addition of GW,in the ?CDM model,the parameter estimations of Hubble constant H0 and the matter density ?m are improved 65%and 61%,respectively;in the wCDM model,the parameter estimations of H0,?m and w are improved 77%,76%and 51%.We find that GW could break the parameters degeneracies existing in the current observations,significantly improving the cosmological estimations.Moreover,the parameter-estimation improvement on w indicates that GW is helpful for the research of dark energy.