AMS-02 positron excess: New bounds on dark matter models and hint for primary electron spectrum hardening

The data collected by ATIC, CREAM and PAMELA all display remarkable cosmic ray nuclei spectrum hardening above the magnetic rigidity similar to 240 GV. One natural speculation is that the primary electron spectrum also gets hardened (possibly at similar to 80 CV) and the hardening partly accounts for the electron/positron total spectrum excess discovered by ATIC, HESS and Fermi-LAT. If it is the case, the increasing behavior of the subsequent positron-to-electron ratio will get flattened and the spectrum hardening should be taken into account in the joint fit of the electron/positron data otherwise the inferred parameters will be biased. Our joint fits of the latest AMS-02 positron fraction data together with the PAMELA/Fermi-LAT electron/positron spectrum data suggest that the primary electron spectrum hardening is needed in most though not all modelings. The bounds on dark matter models have also been investigated. In the presence of spectrum hardening of primary electrons, the amount of dark-matter-originated electron/positron pairs needed in the modeling is smaller. Even with such a modification, the annihilation channel chi chi -> mu(+) mu(-) has been tightly constrained by the Fermi-EAT Galactic diffuse emission data. The decay channel chi -> mu(+) mu(-) is found to be viable. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.