ar X iv : h ep - p h / 97 09 48 5 v 1 2 9 Se p 19 97 Ultra - high energy LSP

We argue that the lightest supersymmetric particles (LSP) can be produced with extremely high energies E > ∼ 10 10 GeV in the Universe at the present epoch. Their most probable sources are decaying superheavy particles produced by topological defects or as relic Big Bang particle. We discuss the mechanisms of production of LSP at ultra-high energies (UHE) and the interaction of the UHE LSP with matter. The most attention is given to the neutralino as LSP, although the gluino is also considered as a phenomenological possibility. 1 Introduction Cold Dark Matter (CDM) is probably the most abundant form of matter in the Universe. A natural CDM candidate is the lightest supersymmetric particle (LSP) which is stable, if R-parity is conserved. In this Letter, we address the question if the LSP can be also among the ultra-high energy (UHE) particles filling the Universe. Theoretically the best motivated candidates for LSP are the neutralino and gravitino. We shall not consider the latter, because it is practically undetectable as UHE particle. Therefore, we pay most attention to the neutralino. In all elaborated SUSY models the gluino is not the LSP. Only, if the dimension-three SUSY breaking terms are set to zero by hand, gluino with mass m ˜ g = O(1 GeV) can be the LSP [1]. There is some controversy if the low-mass window 1 GeV < ∼ m ˜ g < ∼ 4 GeV for the gluino is still allowed [2,3]. Nevertheless, we shall study the production of high-energy gluinos and their interaction with matter being inspired by the recent suggestion [4] (see also [5]), that the atmospheric showers observed at the highest energies can be produced by colourless hadrons containing gluinos. We shall refer to any of such hadron as˜g-hadron in some detail in the literature in connection with Cyg X-3 [6,7]. Additionally, we consider heavy gluinos with m ˜ g > ∼ 150 GeV [5]. Three mechanisms for the production of UHE LSP can be identified. (i) They can be produced in " astrophysical accelerators " due to the interaction of accelerated protons with ambient gas. This mechanism effectively works only in the case of a light gluino, and it was exploited in 80s during the Cyg X-3 epic where the glueballino (˜ gg bound state) was one of the main characters [6,7]. For UHE˜g-hadrons this production mechanism was indicated in Ref. [4]. The main difficulty of this …