Dark Matter And Dark Energy Interaction Model With Parameters Calculated

After Einstein supposed a cosmology model with a constant,the issues about cosmology are widely drew attentions all over the world.Especially,as the observational technologies become more and more advanced,the problems referring to dark matter and dark energy are becoming the most hottest topics today.In order to explain the observed cosmic acceleration,it is necessary to require the existence of dark matter and dark energy.There are mainly two aspects.The first view considers that dark matter and dark energy are really existed,which can be described by the forms of perfect fluid or particular field.Just because of the negative pressure supported by dark energy,the universe is propelled to accelerate expansion. This contains ACDM,ωCDM,Brans-Dicke,tachyon models,etc.In chapterⅠ,the holographic dark energy model is investigated,as well,it is concluded that there is a small interaction between dark matter and dark energy.The research shows within the 1σrange,the equation of state of hologaphic dark energy can transit fromω＞-1 toω＜-1.The best fit deceleration factor buttresses the fact of the current observed acceleration. And from the calculation of entropy,the interaction brought in between dark matter and dark energy does not violate the second law of thermodynamics.However, the sign of the interaction's magnitude has brought a few arguments.Therefore,the specific study focused on this point is done in ChapterⅡ.We have analyzed the compatibilities among different observational data sets without choosing particular models for dark energy,and find out that the interaction between dark matter and dark energy is a small positive value.This discovery can alleviate the coincidence problem,meanwhile satisfy the second law of thermodynamics.The second view considers that the geometry of the space and time leads to the acceleration. If dark energy is regarded as a geometric effect,dark energy is not necessary to exist,but explain what we have observed now by modifying the geometric structure of space and time.f(R) gravity can provide us with a possible way.In ChapterⅢ,the simplest f(R) gravity and matter-curvature coupling f(R) models are investigated.In order to judge the validity of the model comprehensively,it is very necessary to adopt the observational data to constrain the models. Two types of data are mostly used.One is based on the cosmic expansion history, such as the new type Ia supernova samples,the shift parameter of the Cosmic Microwave Background given by the three-year Wilkinson Microwave Anisotropy Probe observations,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and H(z) data,etc.Another is based on time-dependant measurements such as age estimates of 35 galaxies,X-rays of galaxies,etc.We have adopted these data to constrain the parameters of the models in chapterⅠ,Ⅱ,Ⅲ.We have mainly used the Markov Chain Monte Carlo algorithm to performχ~2 statistics to the errors between the theoretical predictions and actual observations.In chapterⅣ,the numerical methods mainly concerning about the MCMC are briefly summarized.