MeV-GeV $\gamma$-ray telescopes probing gravitino LSP with coexisting axino NLSP as dark matter in the $\mu \nu$SSM

Abstract

In $R$-parity violating supersymmetry, the gravitino as the lightest supersymmetric particle (LSP) is a good candidate for dark matter, with the interesting characteristic to be detectable through $\gamma$-ray telescopes. We extend this analysis considering an axino next-to-LSP (NLSP) as a coexisting dark matter particle contributing with a detectable signal in the $\gamma$-ray spectrum. The analysis is carried out in the framework of the $\mu \nu$SSM, which solves the $\mu$ problem reproducing simultaneously neutrino data only with the addition of right-handed neutrinos. We find that important regions of the parameter space can be tested by future MeV-GeV $\gamma$-ray telescopes through the line signal coming from the decay of the axino NLSP into photon-neutrino. In a special region, a double-line signal from axino NLSP and gravitino LSP is possible with both contributions detectable.

Comments: Version published in Astroparticle Physics. Discussions expanded, appendix and references added, 23 pages, 4 figures. The analysis of the opposite case (axino LSP with gravitino NLSP) was carried out in arXiv:1911.03191