Probing gravitino dark matter with PAMELA and Fermi

Abstract

Abstract. We analyse the cosmic-ray signatures of decaying gravitino dark matter in a model-independent way based on an operator analysis. Thermal leptogenesis and universal boundary conditions at the GUT scale restrict the gravitino mass to be below 600 GeV. Electron and positron fluxes from gravitino decays, together with the standard GALPROP background, cannot explain both the PAMELA positron fraction and the electron + positron flux recently measured by Fermi LAT. For gravitino dark matter, the observed fluxes require astrophysical sources. The measured antiproton flux allows for a sizable contribution of decaying gravitinos to the gamma-ray spectrum, in particular a line at an energy below 300 GeV. Future measurements of the gamma-ray flux will provide important constraints on possible signatures of decaying gravitino dark matter at the LHC.

New decay modes of gravitino dark matter

“…Notice, from the above equations, that the mixing parameters decrease with gaugino masses. The two-body decays of gravitino dark matter have been studied in detail in previous works [5,7,12]. For gravitino masses below M W , gravitinos decay into γν τ with a 100% branching ratio.…”

SUSY dark matter(s)

“…Regarding the claim of a tentative line at 130 GeV in the Fermi-LAT data [89,100], such a line signal may occur naturally with the correct intensity in bilinear R-parity breaking models, both from gravitino [148,149] or axino [150] DM decay, but unfortunately the morphology of the signal region, which appears strongly concentrated in the galactic center [100,151], is not well-fitted by the more broadly distributed decaying DM signal [148]. On the other hand, decaying gravitino DM can accommodate the positron excess observed by PAMELA [138] and AMS-02 [152].…”

“…Also we show with the green (dotted) line projected limits from ICEcube on the decay into two neutrinos [147] lifetime in a photon line of the order of 5 × 10 28 s [134,135], excluding the R-parity breaking parameter space giving origin to neutrino masses, if the gravitino is heavier than few GeV. The spectra from gravitino decay in bilinear R-parity models have been computed in [132,[136][137][138][139]. In the case of trilinear R-parity breaking, also three-body decays can be important, because the two-body decay only arises at oneloop level [140][141][142].…”

Electromagnetic properties of spin-3/2Majorana particles

“…In the case of the spin-1/2 particles, if we consider the set of all the possible bilinears ω ′ † Γω, where ω and ω ′ are the two-component spinors corresponding to the initial and final particle states, it is not possible construct any higher rank three-dimensional tensors other than the vector ω ′ † σ i ω. This follows from the relations that the spin matrices 28) which is of course a reflection of the fact that, apart from the identity matrix, the Pauli matrices span the space of 2 × 2 matrices. Therefore, the particle can have only electric and magnetic dipole moments.…”

“…This work can also serve as a guide when testing the SM and its extensions, the possible departures from them or the breaking of some fundamental principles such as Lorentz or gauge invariance, and can also be relevant in other problems involving spin-3/2 particles such as spin-3/2 quark searches at the LHC [17] and others [18,19]. In addition, although we limit ourselves here to the spin-3/2 to spin-3/2 electromagnetic vertex, it can also serve as a guide to consider the gravitino-neutrino radiative transition, which has also been of interest in the context of dark matter [20][21][22][23][24][25][26][27][28][29].…”