  Recently, dark matter indirect searches have gained a lot of attention,
mostly due to the possibility of recent anomalies in cosmic rays and microwave
sky maps being due to the annihilation or decay of dark matter. In this thesis,
we argue however that these signals are plagued by irreducible astrophysical
backgrounds and show how plausible conventional physics can mimic the alleged
dark matter signals. In particular, we consider the possibility that the rise
in the positron fraction observed by the PAMELA satellite is due to the
production through (hadronic) cosmic ray spallation and subsequent acceleration
of positrons, in the same sources as the primary cosmic rays. We present a new
analytical estimate of the range of possible fluctuations in the high energy
electron flux due to the discreteness of plausible cosmic ray sources. Fitting
our result for the total electron-positron flux measured by the Fermi satellite
allows us to fix the only free parameter of the model and make an independent
prediction for the positron fraction. This model can be tested by considering
similar effects expected for nuclear secondary-to-primary ratios such as B/C. A
rise predicted above O(100) GeV/n would be an unique confirmation of our
explanation for a rising positron fraction and rule out the dark matter
explanation. Furthermore, we review the assumptions made in the extraction of
the `WMAP haze' which has also been claimed to be due to electrons and
positrons from dark matter annihilation in the Galactic centre region. We argue
that the energy-dependence of their diffusion makes the extraction of the haze
through template fitting unreliable. The systematic effects introduced by this
can, under specific circumstances, reproduce the residual, suggesting that the
`haze' may be just an artefact of the template subtraction.
