5,189 research outputs found
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 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
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