The Pauli Exclusion Principle, Spin, and Statistics in Loop Quantum Gravity: SU(2) versus SO(3)

Recent attempts to resolve the ambiguity in the loop quantum gravity description of the quantization of area has led to the idea that j=1 edges of spin-networks dominate in their contribution to black hole areas as opposed to j=1/2 which would naively be expected. This suggests that the true gauge group involved might be SO(3) rather than SU(2). We argue that the idea that a version of the Pauli principle is present in loop quantum gravity allows one to maintain SU(2) as the gauge group while still naturally achieving the desired suppression of spin-1/2 punctures. Such an idea can be motivated by arguments from geometric quantization even though the SU(2) under consideration does not have the geometrical interpretation of rotations in 3-dimensional space, and its representation labels do not correspond to physical angular momenta. In this picture, it is natural that macroscopic areas come almost entirely from j=1 punctures rather than j=1/2 punctures, and this is for much the same reason that photons lead to macroscopic classically observable fields while electrons do not.Comment: Talk at the 10th Marcel Grossmann Meeting, Rio de Janeiro, July 20-26, 2004. Updated March 29, 2004 with reference to N=1 SUS

The Pierre Auger Observatory

One of the most fascinating puzzles in particle astrophysics today is that of the origin and nature of the highest energy cosmic rays. The Pierre Auger Observatory (PAO), currently under construction in Province of Mendoza, Argentina, and with another site planned in the Northern hemisphere, is a major international effort to make precise, high statistics studies of the highest energy cosmic rays. It is the first experiment designed to work in a hybrid mode incorporating both a ground-based array of 1600 particle detectors spread over 3000 km$^2$ with fluorescence telescopes placed on the boundaries of the surface array. The current status of the observatory is presented and prospects for the future discussed.Comment: To appear in the proceedings of CIPANP 200