Researches On The Anisotropy Of Cosmology And The Alternative Theories Of Dark Matter

Based on the general theory of relativity and cosmological principle,the standard cosmological model??CDM?not only is the simplest model to describe the development of cosmology,but also is highly consistent with a large number of astronomical observations.In?CDM model,Universe is composed of dark energy,dark matter and ordinary baryon matter.And,the space of Universe is homogeneous and isotropic at a large scale.Although the?CDM model has achieved great success,it still faces some challenges.Anomalous phenomena such as hemispherical asymmetry in the power spectrum of microwave background radiation power spectrum and the dipolar spatial variation of the fine-structure constant at the large scale,indicate that Universe may deviate from the cosmological principle,namely statistically isotropic hypothesis.In addition,the dark matter hypothesis has been proposed for about 90 years.The physicists have not found any direct evidence of the existence of dark matter particle,except the evidence of astronomical observations such as galaxy rotation curves and gravitational lenses.Hence,it is necessary to discuss the alternative theories of dark matter.We test theses issues with a variety of astronomical observations in this paper.Firstly,we test the isotropic hypothesis of the?CDM model with two different methods.1)Test with the distance duality relation?DDR?.We parameterize DDR with a aniostropic form to test the spatial structure of Universe.Comparing with the observation data of strong gravitational lens and supernova,we find that the anisotropic amplitude parameter A=0.038±0.063 in the supernova sample Union2.1,which manifests that there is no signal of anisotropy.In the supernova sample JLA,we obtaine an anisotropic amplitude parameter A=0.068±0.049.The results show that no strong evidence is found that Universe is anisotropic.Monte Carlo simulation has verified the statistical significance of our method.And the method can further detect the anisotropic direction,if the anisotropy is confirmed.2)Test with the variation of electromagnetic fine-structure constant.Anomalous phenomena in astronomical observations suggest that there would be some theoretical models beyond the?CDM model.In some anisotropic cosmological models,EM field is coupled to another field,thus the velocity of photon would be modified,causing the variation of?_e.Hence,we can test the anisotropy by detecting the variation of?_e.In the era of gravitational wave?GW?detection,the method to test the cosmology with GW would achive a higher accuracy.In a strongly lensed gravitational waves event accompanied with an electromagnetic counterpart?EM conterpart?,two images of the GW event and two images of the EM counterpart are observed.Because the speeds of photon is modified and gravity travels with the classical speed of light,the GW time delay and EM time delay would be different.The difference between two time delays is capable of testing the variation of?_e.Analyzing the time delay difference between strongly lensed gravitational wave and its EM counterpart,we obtain the detection accuracy of detecting the dipolar variation of ?_e is 1.85×10^-5.Consideing the effect of redshift,the precision is 10^-10.Secondly,we test the alternative theories of dark matter with astronomical observations.1)Test gravity models with galaxy rotation curve.With a sample consisting of 18 galaxy rotation curve,we test three types model,viz.dark matter model,modified Newtonian dynamic model?MOND?,MSTG model.We apply the statistical method to appraise the best-fitting model.The result shows that,only one galaxy can be best fitted by the MSTG model,two galaxies are best accounted for by the standard gravity model which is neither necessary to add the dark matter component,nor necessary to modified gravity,five to six galaxies are best accounted for by the dark matter model,nine to ten galaxies are best fitted by the MOND model.In summary,the MOND model is the best model for this sample.2)Test gravity models with gravitational lensing.Recently,Verlinde analyzed emergent gravity?EG?and obtained the apparent dark matter mass from the entanglement of the microscopic degree of freedom,which is considered as an alternative to dark matter.Therfore,we test the NFW model of dark matter and EG model of Verlinde.Due to that all the best-fitting parameters of EG are at the same order as the theoretical value,EG theory could alternate dark matter in a qualitative way.However,the statistical analysis shows that NFW profile has better performance than EG.