Astrophysical models for the origin of the positron 'excess'

Over the last three years, several satellite and balloon observatories have suggested intriguing features in the cosmic ray lepton spectra. Most notably, the PAMELA satellite has suggested an "anomalous" rise with energy of the cosmic ray positron fraction. In this article, we summarize the global picture emerging from the data and recapitulate the main features of different types of explanations proposed. The perspectives in testing different scenarios as well as inferring some astrophysical diagnostics from current/near future experiments are also discussed.
Comment: 15 pages (150 references), 2 figures: review article for a Topical Issue on Cosmic Rays, matches version appearing in Astroparticle Physics