Microlensing and Halo Cold Dark Matter

We discuss the implications of the more than 50 microlensing events seen by the EROS, MACHO, and OGLE collaborations for the composition of the halo of our galaxy. The event rates indicate that the halo mass fraction in MACHO's is less than 30\%, consistent with expectations for a universe whose primary component is cold dark matter. We caution that the uncertainties are such that a larger MACHO fraction cannot yet be excluded.Comment: 8 pages, latex, 4 figures, (Minor revisions of our galactic models

Treating Solar Model Uncertainties: A Consistent Statistical Analysis of Solar Neutrino Models and Data

We describe how to consistently incorporate solar model uncertainties, along with experimental errors and correlations, when analyzing solar neutrino data to derive confidence limits on parameter space for proposed solutions of the solar neutrino problem. Our work resolves ambiguities and inconsistencies in the previous literature. As an application of our methods we calculate the masses and mixing angles allowed by the current data for the proposed MSW solution using both Bayesian and frequentist methods, allowing purely for solar model flux variations, to compare with previous work. We consider the effects of including metal diffusion in the solar models and also discuss implications for future experiments.Comment: 29 pages (incl figs), latex, 6 figures (appended as separate uuencoded file. To embed figures in text, uncomment 6 \epsfysize lines which appear before bibliography), CWRU-P5-94, CfPA-94-TTH-29, Fermilab-Pub-94/176-

Gravitational Microlensing and the Galactic Halo

By means of extensive galactic modeling we study the implications of the more than eighty microlensing events that have now been observed for the composition of the dark halo of the Galaxy, as well as for other properties of the Galaxy. We take the Galaxy to be comprised of luminous and dark disk components, a bulge, and a dark halo consisting of both MACHOs and cold dark matter with each component being described by several observationally motivated parameters. We pare down an initial model space of millions of galactic models to viable models, those which are consistent with the observational data, including rotation curve, local projected mass density, and microlensing rates toward the LMC and bulge. On the basis of a conservative, minimal set of observational constraints an all-MACHO halo cannot yet be excluded, although in most viable models of the Galaxy the halo MACHO fraction is between 0\% and 30\%, consistent with expectations for a universe whose primary component is cold dark matter. An all-MACHO halo is required to be light, and when data on the local escape velocity and satellite-galaxy proper motions, which probe the extent of the dark halo, are taken into account, models which have a high MACHO mass fraction are ruled out. We also explore the possibility that there are no MACHOs in the halo. Finally, we point out several important tests that could definitively exclude an all-MACHO e.g., optical depth for microlensing which is less than $1.5\times 10^{-7}$ toward the LMC or greater than $3\times 10^{-6}$ toward the bulge.Comment: 19 pages, 13 multipart figures are available at ftp://astro.uchicago.edu/ftp/pub/astro/gyuk