Effects Of Time-varying β Of Type Ia Supernova On Constraining Cosmological Models

The cosmic acceleration discovered at the end of last century has always been one of the biggest puzzles in cosmology.So far,however,we are still in the dark about the nature of this extremely counterintuitive phenomenon.To understand the cosmic acceleration,cosmological observations are of essential importance,and one of the most.powerful probes is the use of type Ia supernovae(SNe Ia).In recent years,more and more SNe Ia.have been discovered,and the systematic errors of SNe Ia.have drawn more and more attentions.There are many factors that can lead to systematic uncertainties of SNe Ia,such as the errors in the photometry,the calibration,the identification of SNe Ia,the selection bias,the intrinsic variation of physical properties SNe Ia,the host-galaxy extinction,the gravitational lensing,and so on.One of the most important factors is the potential supernova evolution,i.e.the possibility for the redshift evolution of the stretch-luminosity parameter α and the color-luminosity parameter β of SNe Ia.The current.studies show that α is still consistent with a constant,but the hints for the evolution of βhave been found.In this thesis,by considering two kinds of cosmological models,namely,interacting dark energy(IDE)models and modified gravity(MG)models,we explore the evolution of β and its effects on parameter estimation.In addition to the SNLS3 data,we also use the latest Planck distance prior data,the galaxy clustering(GC)data extracted from sloan digital sky survey(SDSS)data release 7(DR7)and data release 9(DR9).as well as the direct measurement of Hubble constant from the Hubble Space Telescope(HST)observation.We find that.for all the IDE models and the MG models,adding a parameter of β can reduce χ2 by～36,indicating that a constant β is ruled out at 6σconfidence level.Furthermore,varying β can significantly change the fitting results of various model parameters.for all the IDE models,varying β yields a larger fractional CDM densities Ωc0 and a larger equation of state ω;on the other side,varying β yields a smaller reduced Hubble constant h for the ωCDM model,but has no impact on h for the three IDE models,which implies that there is a degeneracy between h and coupling parameter γ.And then,for all the MG models,a time-varying β always yields a.larger fractional matter density Ωm0 and a smaller reduced Hubble constant h;in addition,it significantly changes the shapes of la and 2σ confidence regions of various MG models,and thus corrects systematic bias for the parameter estimation.Our work shows that β’s evolution is completely independent of the cosmological models in the background,and then highlights the importance of considering the evolution of β in the cosmology-fits.