The origin of the positron excess in cosmic rays

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  • 16 March 2009
Abstract
We show that the positron excess measured by the PAMELA experiment in the region between 10 and 100 GeV is a natural consequence of the standard scenario for the origin of Galactic cosmic rays. The 'excess' is due to positrons created as secondary products of hadronic interactions inside the sources, but the crucial physical ingredient which leads to a natural explanation of the positron flux is the fact that the secondary production takes place in the same region where cosmic rays are being accelerated. Therefore secondary positrons (and electrons) participate in the acceleration process and turn out to have a very flat spectrum, which is responsible, after propagation in the Galaxy, for the observed positron 'excess'. This effect cannot be avoided and there is a wide range of values of the environmental parameters for which an excellent fit to the PAMELA excess can be achieved. Both the normalization and the spectrum are predicted rather unambiguously.

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