Long-lived neutralino and ultra-high energy cosmic rays.

Secondary photons from decays of metastable neutralinos can con-tribute to the ultra-high energy cosmic ray ux. The neutralino pro-duction rate is too low in acceleration mechanisms to aect the cosmic ray spectrum without emitting enormous energy in photons and neu-trinos. However, in top-down models with sources not concentrated in galactic halos, neutralino decays change the spectrum signicantly. We estimate the parameters of a model in which photons from neu-tralino decays are responsible for cosmic ray events with energies above 1020 eV, and gure out distinctive experimental signatures for this model. 1. Current experimental data on ultra-high energy (UHE) cosmic ray (CR) spectrum are controversial. The results of the AGASA experiment [1] indi-cate the absence of the GZK feature [2], a cuto in the spectrum at energies above a few times 1019 eV due to the attenuation of high energy protons on cosmic background radiation. However, recently published spectrum ob-tained by the HIRES experiment [3] exhibits this cuto. Other experiments had either low statistics or insucient precision to clearly support either the absence or the presence of the GZK cuto in the spectrum. On the other hand, all experiments (including HIRES) have observed cosmic rays with energies as high as (1 3) 1020 eV. Recently, impressive correlations have been found [4] between the arrival directions of UHECR