Wave effect on Primordial Black Hole microlensing

In our universe, there is a large amount of matter called "dark matter", which is  different from baryon surrounding us. "What is the dark matter" is still the main problem of physics. Primordial black hole(PBH) is one of the dark matter candidates, and attracting many researchers these days because of the sensational gravitational wave detection by LIGO. PBH is Black hole(BH) made in early universe and different from astronomical BH in that PBH can have large mass range from 10^-5g to 100M_sun (astronomical BH is allowed to have its mass above ~30M_sun). Since the PBH abundance for each mass range is determined by the model of early universe, observational constraint of PBH abundance leads to conatrint the model of early universe.

Then how to constraint the PBH abundance observational? One strong way is using gravitational microlensing. Microlensing is the time variation of a star (or something optically emitting light) caused by the gravitational lensing of massive object, PBH in our case. If all the dark matter in our Milky Way halo is composed of PBH, then we must observe a lot of microlensing event. Comparing the theoretical microlensing event number and observed one, we can get the upper limit of PBH abundance in our Milky Way dark matter halo.

Since our target mass range of PBH is really low around asteroid mass, we cannot neglect the wave effect of lensing. In this work, we calculated it carefully and got final constraint on PBH abundance.