Sommerfeld-Enhanced $J$-Factors For Dwarf Spheroidal Galaxies
  For models in which dark matter annihilation is Sommerfeld-enhanced, the
annihilation cross section increases at low relative velocities. Dwarf
spheroidal galaxies (dSphs) have low characteristic dark matter particle
velocities and are thus ideal candidates to study such models. In this paper we
model the dark matter phase space of dSphs as isotropic and
spherically-symmetric, and determine the $J$-factors for several of the most
important targets for indirect dark matter searches. For Navarro-Frenk-White
density profiles, we quantify the scatter in the $J$-factor arising from the
astrophysical uncertainty in the dark matter potential. We show that, in
Sommerfeld-enhanced models, the ordering of the most promising dSphs may be
different relative to the standard case of velocity-independent cross sections.
This result can have important implications for derived upper limits on the
annihilation cross section, or on possible signals, from dSphs.
