Constraint To Neutrino Masses Hierarchy And The Late Time Evolution Of The Universe With Currently Available Cosmological Observations

With the rapid development and progress of cosmological observation technologies such as cosmic microwave background radiation,large scale structures,and type la supernovae,modern cosmological research has moved from qualitative description to high precision measurement.High-precision cosmological observation data makes it possible to give strong constraint on some basic physical parameters,such as the current expansion rate of the universe and the pro-portion of matter.In this thesis,using cosmological observation data,we will focus on two problems:one is determining the neutrino masses hierarchy,and the other is about the cosmo-logical parameter tension problems.On the one hand,the neutrino oscillations phenomenon found in neutrino detection experiments proves that neutrinos have masses,and that massive neutrinos are also a new physics that beyond the standard model of particle physics supported by exact experimental evidence so far.Since neutrinos have mass,its gravitational effects must have left traces in the evolution of the universe.Thus,it is possible to constrain the masses of neutrinos using the cosmological observation data.On the other hand,there is a more than 3? tension between the Hubble constant H0 given by the Planck satellite's latest observation of cosmic microwave background radiation under the standard cosmological model and that of the distance ladder method.The existence of this discrepancy suggests that the standard cosmological model needs to be extended or there is other unknown physics.Based on General Relativity,this thesis gives a brief introduction of the history of the dy-namic evolution of the background universe and related cosmological observations,and then uses statistical methods to constrain the relevant model parameters.In Chapter 4,a dimension-less parameter is adopted to parameterize the three neutrino mass eigenstates,and the positive or negative of this parameter correspond to the normal or inverted mass hierarchies.It turns out that the neutrinos mass and mass hierarchies are different within three typical dark energy models,i.e.,cosmological constants,dark energy's equation of state is constant,and general dynamic dark energy models.In Chapter 5,by using the model-independent cosmic kinematics approaches,we have studied the influence of space curvature on H0 tension.It is found that the non-zero spatial curvature helps to reduce the H0 tension problem and the current cosmologi-cal observations prefer a closed Universe.In Chapter 6,using the Gaussian Processes method,we have reconstructed the expansion history H(z)of the Universe and then reconstructed the growth history with the help of a general parameterization function.Finally,we compared this reconstructed function with the observation data of f?8(z)and found that the mean value of the Hubble constant has a great impact on the expansion history of the universe and related cosmological parameters.