488 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
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
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
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
Present Constraints on the H-dibaryon at the Physical Point from Lattice QCD
The current constraints from lattice QCD on the existence of the H-dibaryon
are discussed. With only two significant lattice QCD calculations of the
H-dibaryon binding energy at approximately the same lattice spacing, the forms
of the chiral and continuum extrapolations to the physical point are not
determined. In this brief report, we consider the constraints on the H-dibaryon
imposed by two simple chiral extrapolations. In both instances, the
extrapolation to the physical pion mass allows for a bound H-dibaryon or a
near-threshold scattering state. Further lattice QCD calculations are required
to clarify this situation.Comment: 8 pages, 2 figures, 1 table; revised for the journa
The Long and Short of Nuclear Effective Field Theory Expansions
Nonperturbative effective field theory calculations for NN scattering seem to
break down at rather low momenta. By examining several toy models, we clarify
how effective field theory expansions can in general be used to properly
separate long- and short-range effects. We find that one-pion exchange has a
large effect on the scattering phase shift near poles in the amplitude, but
otherwise can be treated perturbatively. Analysis of a toy model that
reproduces 1S0 NN scattering data rather well suggests that failures of
effective field theories for momenta above the pion mass can be due to
short-range physics rather than the treatment of pion exchange. We discuss the
implications this has for extending the applicability of effective field
theories.Comment: 22 pages, 9 figures, references corrected, minor modification
Interplay of gravitation and linear superposition of different mass eigenstates
The interplay of gravitation and the quantum-mechanical principle of linear
superposition induces a new set of neutrino oscillation phases. These ensure
that the flavor-oscillation clocks, inherent in the phenomenon of neutrino
oscillations, redshift precisely as required by Einstein's theory of
gravitation. The physical observability of these phases in the context of the
solar neutrino anomaly, type-II supernovae, and certain atomic systems is
briefly discussed
Building light nuclei from neutrons, protons, and pions
In these lectures I first explain, in a rather basic fashion, the
construction of effective field theories. I then discuss some recent
developments in the application of such theories to two- and three-nucleon
systems.Comment: 54 pages, uses czjphys.cls. Lectures given at 14th Summer School
"Understanding the Structure of Hadrons", Prague, July 2001. To appear in
Czechoslovak Journal of Physic
Lattice Simulations for Light Nuclei: Chiral Effective Field Theory at Leading Order
We discuss lattice simulations of light nuclei at leading order in chiral
effective field theory. Using lattice pion fields and auxiliary fields, we
include the physics of instantaneous one-pion exchange and the leading-order
S-wave contact interactions. We also consider higher-derivative contact
interactions which adjust the S-wave scattering amplitude at higher momenta. By
construction our lattice path integral is positive definite in the limit of
exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4)
positivity and the approximate SU(4) symmetry of the low-energy interactions
play an important role in suppressing sign and phase oscillations in Monte
Carlo simulations. We assess the computational scaling of the lattice algorithm
for light nuclei with up to eight nucleons and analyze in detail calculations
of the deuteron, triton, and helium-4.Comment: 44 pages, 15 figure
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