Tidal evolution of dark matter annihilation rates in subhalos
  Dark matter halos grow by hierarchical clustering as they merge together to
produce ever larger structures. During these merger processes, the smaller halo
can potentially survive as a subhalo of the larger halo, so a galaxy-scale halo
today likely possesses a rich abundance of substructure. This substructure can
greatly boost the rate of dark matter annihilation within the host halo, but
the precise magnitude of this boost is clouded by uncertainty about the
survival prospects of these subhalos. In particular, tidal forces gradually
strip material from the subhalos, reducing their annihilation signals and
potentially destroying them. In this work, we use high-resolution idealized
$N$-body simulations to develop and tune a model that can predict the impact of
this tidal evolution on the annihilation rates within subhalos. This model
predicts the time evolution of a subhalo's annihilation rate as a function of
three physically motivated parameters of the host-subhalo system: the energy
injected into subhalo particles per orbit about the host, the ratio of
stretching to compressive tidal forces, and the radial distribution of tidal
heating within the subhalo. Our model will improve the accuracy of predictions
of the magnitude and morphology of annihilation signals from dark matter
substructure. Additionally, our parametrization can describe the time evolution
of other subhalo properties, so it has implications for understanding aspects
of subhalo tidal evolution beyond the annihilation rate.
