  The unambiguous detection of Galactic dark matter annihilation would unravel
one of the most outstanding puzzles in particle physics and cosmology. Recent
observations have motivated models in which the annihilation rate is boosted by
the Sommerfeld effect, a non-perturbative enhancement arising from a long range
attractive force. Here we apply the Sommerfeld correction to Via Lactea II, a
high resolution N-body simulation of a Milky-Way-size galaxy, to investigate
the phase-space structure of the Galactic halo. We show that the annihilation
luminosity from kinematically cold substructure can be enhanced by orders of
magnitude relative to previous calculations, leading to the prediction of
gamma-ray fluxes from up to hundreds of dark clumps that should be detectable
by the Fermi satellite.
