88 research outputs found
Coherent bubble-sum approximation for coupled-channel resonance scattering
For coupled-channel resonance scattering we derive a model with a closed form
solution for the -matrix that satisfies unitarity and analyticity. The
two-channel case is handled explicitly for an arbitrary number of resonances.
The method focuses on the expansion of the transition matrix elements,
, in known analytical functions. The appropriate hadronic form
factors and the related energy shifts can be determined from the scattering
data. The differences between this method and the -matrix and the
Breit-Wigner approximation are illustrated in the case of the
resonances and .Comment: 8 pages, 1 figure, code available from
http://www.phyast.pitt.edu/~norbertl/bubblegum2
Search for methylamine in high mass hot cores
We aim to detect methylamine, CHNH, in a variety of hot cores and
use it as a test for the importance of photon-induced chemistry in ice mantles
and mobility of radicals. Specifically, CHNH cannot be formed from atom
addition to CO whereas other NH-containing molecules such as formamide,
NHCHO, can. Submillimeter spectra of several massive hot core regions were
taken with the James Clerk Maxwell Telescope. Abundances are determined with
the rotational diagram method where possible. Methylamine is not detected,
giving upper limit column densities between 1.9 6.4 10
cm for source sizes corresponding to the 100 K envelope radius. Combined
with previously obtained JCMT data analyzed in the same way, abundance ratios
of CHNH, NHCHO and CHCN with respect to each other and
to CHOH are determined. These ratios are compared with Sagittarius B2
observations, where all species are detected, and to hot core models. The
observed ratios suggest that both methylamine and formamide are overproduced by
up to an order of magnitude in hot core models. Acetonitrile is however
underproduced. The proposed chemical schemes leading to these molecules are
discussed and reactions that need further laboratory studies are identified.
The upper limits obtained in this paper can be used to guide future
observations, especially with ALMA.Comment: 14 pages, 5 figures, accepted for publication in A&
A simple plan for the Delta resonance
We construct the resonance as a superposition of a bare
state and the continuum. It is parametrized by three coupling constants
for local and couplings and the mass. The
latter incorporates the mass renormalization due to the
interaction, while the results depend only weakly, if at all, on its
wave-function renormalization. Three more renormalization constants are needed
for the derivative contact interaction. They allow one to generate the
resonance dynamically. A large number of fits test the quality of different
model assumptions in the , and p-wave
scattering channels.Comment: 8 pages, 5 figures, submitted to the proceedings of the PWA Workshop
at CMU, June 2002, some typos and style issues resolved. (a special issue of
International Journal of Modern Physics A
Towards a Many-Body Treatment of Hamiltonian Lattice SU(N) Gauge Theory
We develop a consistent approach to Hamiltonian lattice gauge theory, using the maximal-tree gauge. The various constraints are discussed and implemented. An independent and complete set of variables for the colourless sector is determined. A general scheme to construct the eigenstates of the electric energy operator using a symbolic method is described. It is shown how the one-plaquette problem can be mapped onto a N-fermion problem. Explicit solutions for U(1), SU(2), SU(3), SU(4), and SU(5) lattice gauge theory are shown
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