24,002 research outputs found
Constraints on the Decomposition of the Rotation Curves of Spiral Galaxies
I discuss anew how arguments about the internal dynamics of galactic disks
set constraints on the otherwise ambiguous decomposition of the rotation curves
of spiral galaxies into the contributions by the various constituents of the
galaxies. Analyzing the two sample galaxies NGC 3198 and NGC 2985 I conclude
from the multiplicities of the spiral arms and the values of the Q disk
stability parameters that the disks of both galaxies are `maximum disks'.Comment: Latex, 6 pages, 4 figures, contributed talk at the IDM2002
conference, Sept. 2 - 6 2002, in York, Englan
Density waves in the shearing sheet III. Disc heating
The problem of dynamical heating of galactic discs by spiral density waves is
discussed using the shearing sheet model. The secular evolution of the disc is
described quantitatively by a diffusion equation for the distribution function
of stars in the space spanned by integrals of motion of the stars, in
particular the radial action integral and an integral related to the angular
momentum. Specifically, disc heating by a succession of transient, `swing
amplified' density waves is studied. It is shown that such density waves lead
predominantly to diffusion of stars in radial action space. The stochastical
changes of angular momenta of the stars and the corresponding stochastic
changes of the guiding centre radii of the stellar orbits induced by this
process are much smaller.Comment: 6 pages, 1 figure, accepted by MNRA
Higher level WZW sectors from free fermions
We introduce a gauge group of internal symmetries of an ambient algebra as a
new tool for investigating the superselection structure of WZW theories and the
representation theory of the corresponding affine Lie algebras. The relevant
ambient algebra arises from the description of these conformal field theories
in terms of free fermions. As an illustration we analyze in detail the \son\
WZW theories at level two. In this case there is actually a homomorphism from
the representation ring of the gauge group to the WZW fusion ring, even though
the level-two observable algebra is smaller than the gauge invariant subalgebra
of the field algebra.Comment: LaTeX2e, 30 page
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