Positrons from cosmic rays interactions and dark matter annihilations
  The electron and positron cosmic rays puzzle has triggered a revolution in
the field of astroparticle physics. Many hypotheses have been proposed to
explain the unexpected rise of the positron fraction, observed by HEAT and
PAMELA experiments, for energies larger than few GeVs. In this work, we study
sources of positron cosmic rays related to annihilation of dark matter and
secondary production. In both cases, we consider the impact of uncertainties
related to dark matter physics, nuclear physics and propagation of cosmic rays,
finding that the largest uncertainties come from propagation. We find that some
key features present in the positron signal from dark matter annihilation are
preserved even though the uncertainties. In addition, we study the stability of
the positron fraction under small variations of the electron flux, which is
usually considered as known, we found that considering just the observational
uncertainties in the electron flux is enough to changed dramatically the
positron fraction in the energy range were the excess is observed.
