Lensing Budget in the Dominate Brown Dwarfs of Halo: A Possible Solution for the Microlensing Problems

For searching gravitational microlensing events, millions of stars in the Large Magellanic Cloud (LMC) have been monitored for one decade and only a dozen of events have been detected. The low number of events causes ambiguities in studying the mean mass of MACHOs and their contribution to the Milky Way halo mass due to Poisson fluctuation. The results obtained by the microlensing experiments, are in discrepancy with other observations in some cases. The outline of discrepancies are (i) the incompatibility of the distribution of events duration in the galactic models and observed data, (ii) the lack of abundant white dwarfs in the galactic halo and (iii) undetected heavy elements in the galactic halo that would be caused by the white dwarfs evolution and the supernova explosions. Here we use the ansatz of a spatially varying mass function of MACHOs and repeat the microlensing analysis. According to this model, massive MACHOs reveal themselves more frequently in the microlensing events than the brown dwarfs which have a higher abundance. This point may resolve the mentioned contradictory between the microlensing results and the other observations.