Dark matter in the Galactic Bulge: a Microlensing point of view

Microlensing is one of the most promising technique to probe the densityof dark matter in the Galactic Bulge. We review briefly the history ofmicrolensing and comment on the discovery of high optical depthin the direction of the Bulge. This optical depth is several timeslarger than the first theoretical predictions. We will show that someof the discrepancy can be resolved by taking into account the effectof self amplification of stars into the Galactic Bar. We will alsoexplain that the optical depth is contaminated with the contributionof faint unresolved stars. However, we emphasize that a categoryof sources, the bulge giants are bright enough to escape the biasdue to unresolved sources. Finallywe show that even if self amplification in the bar is taken into account, the optical depth to giants is hard to reproduce. We concludeby saying that in the near future this excess in the bulge opticaldepth should be clarified and measured with good accuracy. In particulargood progress should be made when the analyze of the last observationsof Bulge giants will be completed by the MACHO group. The futureimplementation of the image subtraction technique in the data pipelinesshould also help to overcome the bias in the measurement of the opticaldepth to turnoff stars. This revised version was published online in July 2006 with corrections to the Cover Date.