The Study On The Primordial Black Holes And Bosonic Dark Matter

Astronomical observations indicate that the matter in the universe includes 4.9% ordinary matter,26.8% dark matter and 68.3% dark energy.Although dark matter has not been detected directly,there is a lot of phenomenon indicating that it does exist,such as the galactic rotation curves,gravitational lensing,etc.The standard model of cosmology and the relevant evidence of dark matter are first discussed in this paper.And then primordial black holes(PBH)are introduced.The PBH is black holes produced in the radiation era by the gravitational collapse of density perturbations generated during inflation.To produce appreciable abundance of PBH dark matter,the curvature power spectrum at small scales should be amplified to the order of 0.01 near the end of inflation,so the slow-roll parameter ? is required to decrease by at least 7 orders of magnitude.We propose the conditions to successfully produce PBHs,and we use a toy model with the polynomial potential to realize the enhancement of the power spectrum by 7 orders of magnitude,and we also compute the second order gravitational waves caused by density perturbations.The power spectrum for the second order gravitational waves generated by the large density perturbations is consistent with the current PTA observations,and can be tested by future PTA and space-borne gravitational wave observations.And then three bosons dark matter candidates are introduced,including axion,axion like particle(ALP),and dark photon.All the three candidates of dark matter can be generated by the misalignment mechanism.The axion and axion like particle have similar features,which correspond to spin 0,while the spin of dark photon is 1.For these three models,although the decay rate is very small,the huge number of dark matter in the galaxies lead to the decay signal can be detected.After calculating the decay rate of dark matter,we find the decay spectrum of dark photon and axion/ALP both have a sharp peak.Combined with current laboratory detection experiments,the detection for the nearby galactic halos may reveal the nature of dark matter.In addition,we propose a new kind of experiment,which use atomic energy level transition to detect dark photon.The energy gap between 2S state and 2P state can be adjusted by external magnetic field for hydrogen or hydrogen like ions,in order to matching with the energy of dark photon.Then the photons from the transition of 2P state to 1S state can be detected.The experiment scheme was based on the fact that the interaction Lagrangian of dark photon and the quantum electrodynamics are similar,except that the interaction Lagrangian of dark photon has a suppressing factor,and for this reason the experiment should be done in the very low temperature to avoid thermal noise.We find that the ALP can be used to explain hemisphere asymmetry of power spectrum of the cosmic microwave background radiation(CMB).Considering the general ALP scalar field,which broke its symmetry spontaneously before the inflation,this process produce a cosmic string,which causes the variation of the ALP field.After inflation,this scalar field decays into radiation before big bang nucleosynthesis.If we choose the appropriate value of scale of spontaneous broken symmetry and the strength of self-coupling,the observed CMB power spectrum asymmetry can then be explained naturally.This indicates that ALP may exist in the nature.In addition,we find that the first order speed equation of ALP has more two terms than point-like dark matter,corresponding to quantum pressure and self-interaction respectively.For the extremely light ALP,these two terms may have measurable consequence.