Related papers: Testing Fundamental Physics with High-Energy Cosmi…
We address some current theoretical issues around ultra-high energy cosmic rays. We recall that scenarios producing more gamma-rays than cosmic rays up to high redshift can in general only provide a sub-dominant contribution to the…
Explanations of the origin of ultra-high energy cosmic rays are severely constrained by the Greisen-Zatsepin-Kuz'min effect, which limits their propagation over cosmological distances. We argue that possible departures from strict Lorentz…
We propose that the origin of ultra-high energy cosmic rays beyond the GZK cutoff and the origin of small cosmological constant can both be explained by vacuum tunneling effects in a theory with degenerate vacua and fermionic doublets. By…
Gamma ray bursts (GRBs) are short and intense pulses of $\gamma$-rays arriving from random directions in the sky. Several years ago Amelino-Camelia et al. pointed out that a comparison of time of arrival of photons at different energies…
Recent results, the present status and the perspectives of high energy gamma-ray astronomy are described. Since the satellite observations by the Compton Gamma Ray Observatory and its precursor missions have been reviewed extensively,…
We will review the main physical aspects of Ultra High Energy Cosmic Rays. We will discuss in particular their propagation through astrophysical backgrounds, focusing on the latest experimental observations of HiRes, Telescope Array and…
Active galaxies and gamma ray bursts are the sources of the highest energy photons detected by astronomical telescopes. We speculate that they may be the sources of the highest energy cosmic rays. This makes them true proton accelerators,…
Historically cosmic rays have always been at the intersection of astrophysics with particle physics. This is still and especially true in current days where experimenters routinely observe atmospheric showers from particles whose energies…
Cosmic rays are the most outstanding example of accelerated particles. They are about 1\% of the total mass of the Universe, so that cosmic rays would represent by far the most important energy transformation process of the Universe.…
Cosmic ray particles with energies in excess of 10**(20) eV have been detected. The sources as well as the physical mechanism(s) responsible for endowing cosmic ray particles with such enormous energies are unknown. This report gives a…
High-energy photons are a powerful probe for astrophysics and for fundamental physics under extreme conditions. During the recent years, our knowledge of the most violent phenomena in the universe has impressively progressed thanks to the…
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.
I discuss recent advances being made in the physics and astrophysics of cosmic rays and cosmic gamma-rays at the highest observed energies as well as the related physics and astrophysics of very high energy cosmic neutrinos. I also discuss…
Ultrahigh energy cosmic rays are the most energetic of any subatomic particles ever observed in nature. The quest for their mysterious origin is currently a major scientific challenge. Here we explore the possibility that these particles…
Even a fundamental symmetry like Lorentz Invariance is an experimental fact and must be experimentally verified. We show that the study of the interactions of Cosmic Rays with universal diffuse background radiation can provide very…
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…
Based on a model for the emission of high energy cosmic rays from AGN (Active Galactic Nuclei) that has been proposed by the author, he reviews the status of the GZK cutoff and the correlation of high energy cosmic ray sources with AGN…
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…
The properties of strangelets are reviewed and two experiments searching for them in cosmic rays are described. The prospects for strangelets as ultra-high energy cosmic rays beyond the classical GZK-cutoff are discussed.
I give a concise introduction into high energy cosmic ray physics, including also few related aspects of high energy gamma-ray and neutrino astrophysics. The main emphasis is placed on astrophysical questions, and the level of the…