17,819 research outputs found
Flavor Doubling and the Nature of Asymptopia
We consider the possibility that QCD with N flavors has a useful low-energy
description with 2N flavors. Specifically, we investigate a free theory of 2N
quarks. Although the free theory is U(N)_L X U(N)_R invariant, it admits a
larger U(2N) invariance. However, when the axial anomaly is accounted for in
the effective theory by a 't Hooft interaction, only SU(N)_L X SU(N)_R X U(1)_B
\subset U(2N) survives. There is however a residual discrete symmetry that is
not a symmetry of the QCD lagrangian. This S_2 subgroup of U(2N) has many
interesting properties. For instance, when explicit chiral symmetry breaking
effects are present, S_2 is broken unless \bar\theta=0 or pi. By expressing the
free theory on the light-front, we show that flavor doubling implies several
superconvergence relations in pion-hadron scattering. Implicit in the 2N-flavor
effective theory is a Regge trajectory with vacuum quantum numbers and unit
intercept whose behavior is constrained by S_2. In particular, S_2 implies that
forward pion-hadron scattering becomes purely elastic at high-energies, in good
agreement with experiment.Comment: 26 pages TeX, uses mtexsis.te
A Code Phase Division Multiple Access (CPDMA) technique for VSAT satellite communications
A reference concept and implementation relevant to the application of Code Phase Division Multiple Access (CPDMA) to a high capacity satellite communication system providing 16 Kbps single hop channels between Very Small Aperture Terminals (VSAT's) is described. The description includes a potential implementation of an onboard CPDMA bulk demodulator/converter utilizing programmable charge coupled device (CCD) technology projected to be available in the early 1990's. A high level description of the system architecture and operations, identification of key functional and performance requirements of the system elements, and analysis results of end-to-end system performance relative to key figures of merit such as spectral efficiency are also provided
The fate of cannibalized fundamental-plane ellipticals
Evolution and disruption of galaxies orbiting in the gravitational field of a
larger cluster galaxy are driven by three coupled mechanisms: 1) the heating
due to its time dependent motion in the primary; 2) mass loss due to the tidal
strain field; and 3) orbital decay. Previous work demonstrated that tidal
heating is effective well inside the impulse approximation limit. Not only does
the overall energy increase over previous predictions, but the work is done
deep inside the secondary galaxy, e.g. at or inside the half mass radius in
most cases. Here, these ideas applied to cannibalization of elliptical galaxies
with fundamental-plane parameters. In summary, satellites which can fall to the
center of a cluster giant by dynamical friction are evaporated by internal
heating by the time they reach the center. This suggests that true
merger-produced multiple nuclei giants should be rare. Specifically,
secondaries with mass ratios as small as 1\% on any initial orbit evaporate and
those on eccentric orbits with mass ratios as small as 0.1\% evolve
significantly and nearly evaporate in a galaxian age. Captured satellites with
mass ratios smaller than roughly 1\% have insufficient time to decay to the
center. After many accretion events, the model predicts that the merged system
has a profile similar to that of the original primary with a weak increase in
concentration.Comment: 19 pages, 10 Postscript figures, uses aaspp4.sty. Submitted to
Astrophysical Journa
Note on the thermal history of decoupled massive particles
This note provides an alternative approach to the momentum decay and thermal
evolution of decoupled massive particles. Although the ingredients in our
results have been addressed in Ref.\cite{Weinberg}, the strategies employed
here are simpler, and the results obtained here are more general.Comment: JHEP style, 4 pages, to appear in CQ
Quantum electrodynamics for vector mesons
Quantum electrodynamics for mesons is considered. It is shown that, at
tree level, the value of the gyromagnetic ratio of the is fixed to 2
in a self-consistent effective quantum field theory. Further, the mixing
parameter of the photon and the neutral vector meson is equal to the ratio of
electromagnetic and strong couplings, leading to the mass difference
at tree order.Comment: 4 pages, 2 figures, REVTeX 4, accepted for publication in PR
On the Creation of the Universe out of Nothing
We explain how the Universe was created with no expenditure of energy or
initial mass.Comment: To be presented at IWARA 2009 (4th International Workshop on
Astronomy and Relativistic Astrophysics), to be held in Brazil, October 200
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