The Top--Down Interpretation of Ultra--High Energy Cosmic Rays

Abstract

The origin of Ultra--High Energy ($E\text{gsim}10^{20}$ eV) Cosmic Rays (UHECR) remains mysterious. I discuss ``top--down'' models, where UHECR originate from the decay of very massive, long--lived particles. I summarize the calculation of the spectrum of decay products, discuss possible problems with this scenario, and describe ways to test it by searching for very energetic neutrinos and neutralinos.

Comments: LaTeX, 6 pages; invited talk at VHEPA-3, ICRR, Tokyo, March 2003