A new look at microlensing limits on dark matter in the Galactic halo
  The motivation for this paper is to review the limits set on the MACHO
content of the Galactic halo by microlensing experiments in the direction of
the Large Magellanic Cloud. This has been prompted by recent measurements of
the Galactic rotation curve, which suggest that the limits have been biassed by
the assumption of an over-massive halo. The paper first discusses the security
of the detection efficiency calculations which are central to deriving the
MACHO content of the Galactic halo. It then sets out to compare the rotation
curves from various halo models with recent observations, with a view to
establishing what limits can be put on an all-MACHO halo. The main thrust of
the paper is to investigate whether lighter halo models which are consistent
with microlensing by an all-MACHO halo are also consistent with recent measures
of the Galactic rotation curve. In this case the population of bodies
discovered by the MACHO collaboration would make up the entire dark matter
content of the Galactic halo. The main result of this paper is that it is easy
to find low mass halo models consistent with the observed Galactic rotation
curve, which also imply an optical depth to microlensing similar to that found
by the MACHO collaboration. This means that all-MACHO halos cannot be ruled out
on the basis of their observations. In conclusion, limits placed on the MACHO
content of the Galactic halo from microlensing surveys in the Magellanic Clouds
are inconsistent and model dependent, and do not provide a secure basis for
rejecting an all-MACHO halo.
