  We present robust constraints from the Sloan Digital Sky Survey (SDSS) on the
shape and distribution of the dark matter halo within the Milky Way (MW). Using
the number density distribution and kinematics of SDSS halo stars, we probe the
dark matter distribution to heliocentric distances exceeding 10 kpc and
galactocentric distances exceeding 20 kpc. Our analysis utilizes Jeans
equations to generate two-dimensional acceleration maps throughout the volume;
this approach is thoroughly tested on a cosmologically derived N-body+SPH
simulation of a MW-like galaxy. We show that the known accelerations (gradients
of the gravitational potential) can be successfully recovered in such a
realistic system. Leveraging the baryonic gravitational potential derived by
Bovy & Rix (2013), we show that the gravitational potential implied by the SDSS
observations cannot be explained, assuming Newtonian gravity, by visible matter
alone: the gravitational force experienced by stars at galactocentric distances
of 20 kpc is as much as three times stronger than what can be attributed to
purely visible matter. We also show that the SDSS data provide a strong
constraint on the shape of the dark matter halo potential. Within
galactocentric distances of 20 kpc, the dark matter halo potential is well
described as an oblate halo with axis ratio qDM=0.7+/-0.1; this corresponds to
an axis ratio qDM=0.4+/-0.1 for the dark matter density distribution. Because
of our precise two-dimensional measurements of the acceleration of the halo
stars, we can reject several MOND models as an explanation of the observed
behavior.
