Abstract
Abstract
The phenomenology of diffuse radio emission from Dark Matter
annihilation or decay in dwarf spheroidal galaxies is examined. We
introduce (in the context of cosmic-ray physics) a novel strategy
for the computation of the relevant synchrotron signals. In
particular, we identify various regimes where, in analogy to prompt
gamma rays, the diffuse radio signal from dark matter
annihilation/decay can be expressed as the multiplication of a halo
times a spectral function. These functions are computed here for
the first time for a number of benchmark cases. Furthermore, we
find parameter regions in which the emissivity can be well
approximated by a universal function ∼ sin(π r/r
h)/r, where
r is the galacto-centric distance and r
h the diffusion-zone
radius of the galaxy. Our theoretical setup differs from previous
work in that, instead of employing a method-of-images strategy, we
consider a Fourier-mode expansion of the relevant Green's functions.
With this strategy, exact results can be obtained with very low
computational cost and for generic dark matter models. In
particular, 𝒪(10–100) Fourier modes can be easily
incorporated into the computations in order to probe the smallest
scales of the problem. We also propose a new strategy to search for
dark matter using radio observations of dwarf galaxies that is (1)
easy to implement and (2) free of the otherwise large degeneracies
in the description of synchrotron signals from dark matter.
Finally, we correct a mistake in a widely used Green's function
formula in this context. We show that the original expression leads
to systematically incorrect — and in some cases divergent —
results in the regime where the characteristic time-scale for
diffusion is smaller than that for energy losses.
Subject
Astronomy and Astrophysics
Cited by
12 articles.
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