Fractal Electromagnetic Showers

We study the self-similar structure of electromagnetic showers and introduce the notion of the fractal dimension of a shower. Studies underway of showers in various materials and at various energies are presented, and the range over which the fractal scaling behaviour is observed is discussed. Applications to fast shower simulations and identification, particularly in the context of extensive air showers, are also discussed.Comment: Talk to be presented at the XI International Symposium on Very High Energy Cosmic Ray Interaction

Using {\sc top-c} for Commodity Parallel Computing in Cosmic Ray Physics Simulations

{\sc top-c} (Task Oriented Parallel C) is a freely available package for parallel computing. It is designed to be easy to learn and to have good tolerance for the high latencies that are common in commodity networks of computers. It has been successfully used in a wide range of examples, providing linear speedup with the number of computers. A brief overview of {\sc top-c} is provided, along with recent experience with cosmic ray physics simulations.Comment: Talk to be presented at the XI International Symposium on Very High Energy Cosmic Ray Interaction

Simulation of Water Cerenkov Detectors Using {\sc geant4}

We present a detailed simulation of the performance of water Cerenkov detectors suitable for use in the Pierre Auger Observatory. Using {\sc geant4}, a flexible object-oriented simulation program, including all known physics processes, has been developed. The program also allows interactive visualization, and can easily be modified for any experimental setup.Comment: Talk to be presented at the XI Symposium on Very High Energy Cosmic Ray Interaction

Massive relic neutrinos in the galactic halo and the knee in the cosmic ray spectrum

Despite many efforts to find a reasonable explanation, the origin of the ”knee” in the cosmic ray spectrum at E ≈ 10015.5 eV remains mysterious. In this letter we suggest that the ”knee” may be due to a GZK-like effect of cosmic rays interacting with massive neutrinos in the galactic halo. Simple kinematics connects the location of the ”knee” with the mass of the neutrinos, and, while the required interaction cross section is larger than that predicted by the Standard Model, it can be accommodated by a small neutrino magnetic dipole moment. The values for the neutrino parameters obtained from the analysis of existing experimental data are compatible with present laboratory bounds.Facultad de Ciencias Exacta

Unmasking the tail of the cosmic ray spectrum

A re-examination of the energy cosmic ray spectrum above $10^{20}$ eV is presented. The overall data-base provides evidence, albeit still statistically limited, that non-nucleon primaries could be present at the end of the spectrum. In particular, the possible appearance of superheavy nuclei (seldom discussed in the literature) is analysed in detail.Comment: To appear in Phys. Lett. B with the title ``Possible explanation for the tail of the cosmic ray spectrum'

A Method to Determine the Tau Neutrino Helicity Using Polarized Taus

A method is presented to extract the tau neutrino helicity, or equivalently, the chirality parameter $\gamma_{\mathrm{VA}}$, independent of any tau polarization which may be present. The method is thus well-suited to measurements using taus produced from the $Z^0$ and is complementary to analyses using tau correlations since it provides the sign of the chirality parameter which is otherwise unavailable without recourse to lower energy experiments where taus are unpolarized. Results of Monte Carlo studies and comments regarding the use of the technique in experiments are also included.Comment: 13 pages, uuencoded postscript fil

A pot of gold at the end of the cosmic "raynbow"?

We critically review the common belief that ultrahigh energy cosmic rays are protons or atomic nuclei with masses not exceeding that of iron. We find that heavier nuclei are indeed possible, and discuss possible sources and acceleration mechanisms for such primaries. We also show detailed simulations of extensive air showers produced by ``superheavy'' nuclei, and discuss prospects for their detection in future experiments.Comment: Talk to be presented at the International Symposium on Very High Energy Cosmic Ray Interactions X

On the nature of cosmic rays above the Greisen--Zatsepin--Kuz'min cut off

A re-examination of the atmospheric cascade profile of the highest energy cosmic ray is presented. The study includes air-shower simulations considering different cross sections, particle multiplicity and variation of the hadronic-event-generator to model interactions above 200 GeV. The analysis provides evidence that a medium mass nucleus primary reproduces the shower profile quite well. This result does not support the idea, increasingly popular at present, that the highest energy particles are protons, derived from the decay of supermassive relic particles. On the other hand, we show that debris of relativistic super-heavy nuclei, which can survive a 100 Mpc journey through the primeval radiation are likely to generate such a kind of cascade.Comment: Revised version, improvements per referee's suggestions. To be published in Phys. Lett.

Wetting films on chemically heterogeneous substrates

Based on a microscopic density functional theory we investigate the morphology of thin liquidlike wetting films adsorbed on substrates endowed with well-defined chemical heterogeneities. As paradigmatic cases we focus on a single chemical step and on a single stripe. In view of applications in microfluidics the accuracy of guiding liquids by chemical microchannels is discussed. Finally we give a general prescription of how to investigate theoretically the wetting properties of substrates with arbitrary chemical structures.Comment: 56 pages, RevTeX, 20 Figure