Multi-wavelength Searches for Particle Dark Matter
  If dark matter particles pair annihilate into stable Standard Model
particles, a population of energetic, non-thermal electrons and positrons is
necessarily produced. The secondary radiation resulting from the energy losses
of this non-standard population (including synchrotron and inverse Compton
up-scattering of background radiation photons) in turn produces a peculiar
multi-wavelength spectrum, extending from radio to gamma-ray frequencies. We
give here an overview of multi-wavelength searches for dark matter, including
the expected injection spectrum and production rate of electrons and positrons
from dark matter annihilation, the computation of the effects of propagation
and energy losses and the actual multi-wavelength emission. We then outline the
application of this general framework to the case of galaxy clusters
(specifically Coma, 1E 0657-56 - the so-called Bullet cluster - and Ophiuchus)
and of dwarf spheroidal galaxies (including Draco, Fornax, Ursa Minor and
Carina). We also review the application of multi-wavelength search strategies
to our own Milky Way, and more specifically to the Galactic center environment,
to dark galactic mini-halos and to the so-called WMAP haze and other radio
data. We argue that multi-wavelength observations will complement gamma-ray
observations as probes of particle dark matter, since the expected luminosities
at different frequencies are generically comparable. The indirect search for
dark matter with astronomical observations at various frequencies is therefore
a crucial and indispensable element in the quest for the fundamental nature of
dark matter.
