In the last few years, data of extraordinary quality on the positron flux or fraction has been collected by several experiments, notably CAPRICE [1], HEAT [2], AMS01 [3], PAMELA [4,5] and AMS-02 [6,7]. The most striking result is the observation of a rise in the positron fraction starting at ∼ 10GeV and extending at least to 350 GeV, as recently confirmed by the AMS-02 Collaboration