756 research outputs found
Crinoids Varied in Color at Le Grand, Iowa (Abstract)
In the Le Grand quarries there is an unusual occurrence of multicolored crinoids. Some of these crinoids are almost black, some are almost white, some are dark brown, some are light brown and some are cream colored. Each species is found always to have the same color. One familiar with the fossils can classify them accurately by the color. Platycrinus symmetricus is a dark brown. Diochrinus inornatus is a chocolate brown and Rhodocrinus kirbyi is almost black. Most of the inadunate species are white. One species with unusual coloring is Rhodocrinus watersianus with a mottled brown calyx and light colored arems
Low Energy Constants from High Energy Theorems
New constraints on resonance saturation in chiral perturbation theory are
investigated. These constraints arise because each consistent saturation scheme
must map to a representation of the full QCD chiral symmetry group. The
low-energy constants of chiral perturbation theory are then related by a set of
mixing angles. It is shown that vector meson dominance is a consequence of the
fact that nature has chosen the lowest-dimensional nontrivial chiral
representation. It is further shown that chiral symmetry places an upper bound
on the mass of the lightest scalar in the hadron spectrum.Comment: 11 pages TeX and mtexsis.te
High Energy Theorems at Large-N
Sum rules for products of two, three and four QCD currents are derived using
chiral symmetry at infinite momentum in the large-N limit. These exact
relations among meson decay constants, axialvector couplings and masses
determine the asymptotic behavior of an infinite number of QCD correlators. The
familiar spectral function sum rules for products of two QCD currents are among
the relations derived. With this precise knowledge of asymptotic behavior, an
infinite number of large-N QCD correlators can be constructed using dispersion
relations. A detailed derivation is given of the exact large-N pion vector form
factor and forward pion-pion scattering amplitudes.Comment: 34 pages TeX and mtexsis.tex, 10 figures (uses epsf
Chiral Dynamics of Low-Energy Kaon-Baryon Interactions with Explicit Resonance
The processes involving low energy and interactions (where
or ) are studied in the framework of heavy baryon chiral
perturbation theory with the (1405) resonance appearing as an
independent field.
The leading and next-to-leading terms in the chiral expansion are taken into
account. We show that an approach which explicitly includes the (1405)
resonance as an elementary quantum field gives reasonable descriptions of both
the threshold branching ratios and the energy dependence of total cross
sections.Comment: 16 pages, 6 figure
Precision calculation of the pi^- deuteron scattering length and its impact on threshold pi-N scattering
We present a calculation of the pi^- d scattering length with an accuracy of
a few percent using chiral perturbation theory. For the first time
isospin-violating corrections are included consistently. Using data on pionic
deuterium and pionic hydrogen atoms, we extract the isoscalar and isovector
pion-nucleon scattering lengths and obtain a^+=(7.6 +/- 3.1) x 10^{-3} mpi^{-1}
and a^-=(86.1 +/- 0.9) x 10^{-3} mpi^{-1}. Via the Goldberger-Miyazawa-Oehme
sum rule, this leads to a charged-pion-nucleon coupling constant g_c^2/4 pi =
13.69 +/- 0.20.Comment: 6 pages, 2 figures. Discussion of several points expanded, references
added in this version, which will appear in Physics Letters
Three particles in a finite volume: The breakdown of spherical symmetry
Lattice simulations of light nuclei necessarily take place in finite volumes,
thus affecting their infrared properties. These effects can be addressed in a
model-independent manner using Effective Field Theories. We study the model
case of three identical bosons (mass m) with resonant two-body interactions in
a cubic box with periodic boundary conditions, which can also be generalized to
the three-nucleon system in a straightforward manner. Our results allow for the
removal of finite volume effects from lattice results as well as the
determination of infinite volume scattering parameters from the volume
dependence of the spectrum. We study the volume dependence of several states
below the break-up threshold, spanning one order of magnitude in the binding
energy in the infinite volume, for box side lengths L between the two-body
scattering length a and L = 0.25a. For example, a state with a three-body
energy of -3/(ma^2) in the infinite volume has been shifted to -10/(ma^2) at L
= a. Special emphasis is put on the consequences of the breakdown of spherical
symmetry and several ways to perturbatively treat the ensuing partial wave
admixtures. We find their contributions to be on the sub-percent level compared
to the strong volume dependence of the S-wave component. For shallow bound
states, we find a transition to boson-diboson scattering behavior when
decreasing the size of the finite volume.Comment: 21 pages, 4 figures, 2 table
Perturbative Effective Theory in an Oscillator Basis?
The effective interaction/operator problem in nuclear physics is believed to
be highly nonperturbative, requiring extended high-momentum spaces for accurate
solution. We trace this to difficulties that arise at both short and long
distances when the included space is defined in terms of a basis of harmonic
oscillator Slater determinants. We show, in the simplest case of the deuteron,
that both difficulties can be circumvented, yielding highly perturbative
results in the potential even for modest (~6hw) included spaces.Comment: 10 pages, 4 figure
Constraining Quark-Hadron Duality at Large-Nc
Quark-meson duality for two-point functions of vector and axial-vector QCD
currents is investigated in the large-Nc approximation. We find that the joint
constraints of duality and chiral symmetry imply degeneracy of excited vector
and axial-vector mesons in the large-Nc limit. We compare model-independent
constraints with expectations based on the Veneziano-Lovelace-Shapiro string
model. Several models of duality are constructed, and phenomenological
implications are discussed.Comment: 16 pages TeX, uses mtexsis.te
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