The nature and origin of ultra-high energy (UHE: referring to > 1019 eV) cosmic rays are great mysteries in modern astrophysics. The current theories for their explanation include the so-called ”top-down” decay scenarios whose main signature is a large ratio of UHE gamma rays to protons. Important step in determining the primary composition at ultra-high energies is the study of air shower deve...

Project GRAND is an extensive air shower array of proportional wire chambers. It has 64 stations in a 100 m x 100 m area; each station has eight planes of proportional wire chambers with a 50 mm steel absorber plate above the bottom two planes. This arrangement of planes, each 1.25 square meters of area, allow an angular measurement for each track to 0.25 in each of two projections. The steel a...

In extensive air showers induced by ultra-high energy (UHE) cosmic rays, secondary particles are produced with energies far above those accessible other means. These extreme can be used to search for new physics. We study the effects of isotropic, nonbirefringent Lorentz violation in photon sector. case a velocity smaller than maximum attainable standard Dirac fermions, vacuum Cherenkov radiati...

In high energy cosmic rays surface arrays, the primary energy is currently determined from the value of the lateral distribution function (LDF) at a fixed optimum distance ropt from the shower core. The value of ropt is mainly related to the geometry of the array and is, therefore, considered as fixed independently of the shower energy or direction. Here, we demonstrate that the dependence of r...

Air showers from cosmic rays emit short, intense radio pulses. LOFAR is a new radio telescope, that is being built in the Netherlands and Europe. Designed primarily as a radio interferometer, the core of LOFAR will have a high density of radio antennas, which will be extremely well calibrated. This makes LOFAR a unique tool for the study of the radio properties of single air showers. Triggering...

The extensive air shower (EAS) experiment KASCADE has been installed at the laboratory site of the Forschungszentrum Karlsruhe. It consists of an extended array of electron detectors and muon detectors as well as of a compact and complex central detector system. The latter contains a scintillator matrix, muon detectors, and a large hadron calorimeter. The main aim of the KASCADE project is the ...

For 50 years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An experiment at SLAC provides a beam test of radio-frequency (rf) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experim...

Most calculations of air shower development have been based on the Bethe-Heitler cross sections for bremsstrahlung and pair production. However, for energetic enough particles, a number of different external factors can reduce these cross sections drastically, slowing shower development and lengthening the showers. Four mechanisms that can suppress bremsstrahlung and pair production cross secti...

Cherenkov telescopes image the Cherenkov emission from air showers. A priori, it is not obvious if the ‘best’ images are achieved by measuring Cherenkov photon angles, i.e. focusing the telescope at infinity, or by considering the air shower as an object to be imaged, in which case one might focus the telescope on the central region of the shower. The issue is addressed using shower simulations...