Ultra High Energy Cosmic Rays from Decaying Superheavy Particles

It is proposed that the highest energy $\sim 10^{20}$eV cosmic ray primaries are protons, decay products of a long-lived progenitor whose high kinetic energy arises from decay of a distant (cosmological) superheavy particle, G. Such a scenario can occur in e.g. SU(15) grand unification and in some preon models, but is more generic; if true, these unusual cosmic rays provide a window into new physics.

The topological defect scenario of origin of the observed highest energy cosmic rays is reviewed. Under a variety of circumstances, topological defects formed in the early Universe can be sources of very massive particles in the Universe today. The decay products of these massive particles may be responsible for the observed highest energy cosmic ray particles above $10^{20}$ eV. Some massive particle production processes involving cosmic strings and magnetic monopoles are di...

We review the basic ideas on the origin of cosmic rays with energy in excess of $\sim 10^{19}$ eV, in the light of the most recent observational findings. The limited statistics of events detected by the two largest experiments currently operating does not allow as yet to claim the detection of the GZK feature in the cosmic ray spectrum or the lack of it. Although extragalactic point sources seem to be preferred on the basis of the small scale anisotropies detected by AGASA, ...

In this talk, I present the last and more precise results obtained in the computation of the final spectra of stable particles issued from the decay of super-heavy X particles (M_X ~ 10^21 to 10^25 eV). Such very energetic decay products, carrying a fraction of the mass of the X particle, are believed to be a plausible explanation for the observed ultra-high energy cosmic rays (UHECR). Combining these results with X-particle models and with a code describing the propagation e...

While several arguments can be proposed against the existence of particles with energy in excess of $(3-5)\times 10^{19}$ eV in the cosmic ray spectrum, these particles are actually observed and their origin seeks for an explanation. After a description of the problems encountered in explaining these ultra-high energy cosmic rays (UHECRs) in the context of astrophysical sources, we will review the so-called {\it Top-Down} (TD) Models, in which UHECRs are the result of the dec...

We propose a formula for flux of extremely high energy cosmic rays (EHECR) through decay of superheavy particles. It is shown that EHECR spectrum reported by AGASA is reproduced by the formula. The presence of EHECR suggests, according to this approach, the existence of superheavy particles with mass of about $7 \times 10^{11}$GeV and the lifetime of about $10^9$ years. Possibility to obtain a knowledge of $\Omega_0$ of the universe from the spectrum of EHECR is also poin...

The most energetic particles ever detected exceed $10^{20}$ eV in energy. Their existence represents at the same time a great challenge for particle physics and astrophysics, and a great promise of providing us for a probe of the validity of the laws of Nature in extreme conditions. We review here the most recent data and the future perspectives for detection of cosmic rays at ultra-high energies, and discuss possible ways of using these data to test the possibility that new ...

We present a brief introduction to the physics of Ultra High Energy Cosmic Rays (UHECRs), concentrating on the experimental results obtained so far and on what, from these results, can be inferred about the sources of UHECRs.

The current status of the ultrahigh energy cosmic ray (UHE CR) enigma and several proposed solutions involving particle physics beyond the standard model are discussed. Emphasis is given to top--down models, and as a main example, supermassive dark matter as galactic source for UHE CR and the status of its experimental signatures (galactic anisotropy, chemical composition and clustering) is reviewed. Then different approaches to calculate fragmentation spectra of supermassive...

We discuss theoretical issues and experimental data that brought the ultra high energy cosmic rays in the list of Nature's greatest puzzles. After many years of research we still do not know how astrophysical acceleration processes can reach energies exceeding 10$^{11}$ GeV. The main alternative {\em top-down} mechanism postulates the existence of super massive $X$-particles that create a particle spectrum extending down to the observed energy through their decay channels...