2,367 research outputs found
The Canonical Nuclear Many-Body Problem as an Effective Theory
Recently it was argued that it might be possible treat the conventional
nuclear structure problem -- nonrelativistic point nucleons interacting through
a static and rather singular potential -- as an effective theory in a
shell-model basis. In the first half of this talk we describe how such a
program can be carried out for the simplest nuclei, the deuteron and 3He,
exploiting a new numerical technique for solving the self-consistent
Bloch-Horowitz equation. Some of the properties of proper effective theories
are thus illustrated and contrasted with the shell model. In the second half of
the talk we use these examples to return to a problem that frustrated the field
three decades ago, the possibility of reducing the effective interactions
problem to perturbation theory. We show, by exploiting the Talmi integral
expansion, that hard-core potentials can be systematically softened by the
introduction of a series of contact operators familiar from effective field
theory. The coefficients of these operators can be run analytically by a
renormalization group method in a scheme-independent way, with the introduction
of suitable counterterms. Once these coefficients are run to the shell model
scale, we show that the renormalized coefficients contain all of the
information needed to evaluate perturbative insertions of the remaining soft
potential. The resulting perturbative expansion is shown to converge in lowest
order for the simplest nucleus, the deuteron.Comment: Latex, 12 pages, 2 figures Talk presented at the International
Symposium on Nuclei and Nucleons, held in honor of Achim Richter Typos
corrected in this replacemen
Energy spectra of two interacting fermions with spin-orbit coupling in a harmonic trap
We explore the two-body spectra of spin- fermions in isotropic harmonic
traps with external spin-orbit potentials and short range two-body
interactions. Using a truncated basis of total angular momentum eigenstates,
non-perturbative results are presented for experimentally realistic forms of
the spin-orbit coupling: a pure Rashba coupling, Rashba and Dresselhaus
couplings in equal parts, and a Weyl-type coupling. The technique is easily
adapted to bosonic systems and other forms of spin-orbit coupling.Comment: 12 pages, 9 figure
Water Ice in 2060 Chiron and its Implications for Centaurs and Kuiper Belt Objects
We report the detection of water ice in the Centaur 2060 Chiron, based on
near-infrared spectra (1.0 - 2.5 micron) taken with the 3.8-meter United
Kingdom Infrared Telescope (UKIRT) and the 10-meter Keck Telescope. The
appearance of this ice is correlated with the recent decline in Chiron's
cometary activity: the decrease in the coma cross-section allows previously
hidden solid-state surface features to be seen. We predict that water ice is
ubiquitous among Centaurs and Kuiper Belt objects, but its surface coverage
varies from object to object, and thus determines its detectability and the
occurrence of cometary activity.Comment: 18 pages, 3 figures, accepted by ApJ Letter
Population of the Scattered Kuiper Belt
We present the discovery of three new Scattered Kuiper Belt Objects (SKBOs)
from a wide-field survey of the ecliptic. This continuing survey has to date
covered 20.2 square degrees to a limiting red magnitude of 23.6. We combine the
data from this new survey with an existing survey conducted at the University
of Hawaii 2.2m telescope to constrain the number and mass of the SKBOs. The
SKBOs are characterized by large eccentricities, perihelia near 35 AU, and
semi-major axes > 50 AU. Using a maximum-likelihood model, we estimate the
total number of SKBOs larger than 100 km in diameter to be N = 3.1 (+1.9/-1.3)
x 10^4 (1 sigma) and the total mass of SKBOs to be about 0.05 Earth masses,
demonstrating that the SKBOs are similar in number and mass to the Kuiper Belt
inside 50 AU.Comment: 15 pages, 3 figure
S-wave scattering of strangeness -3 baryons
We explore the interactions of two strangeness -3 baryons in multiple spin
channels with lattice QCD. This system provides an ideal laboratory for
exploring the interactions of multi-baryon systems with minimal dependence on
light quark masses. Model calculations of the two- system in two
previous works have obtained conflicting results, which can be resolved by
lattice QCD. The lattice calculations are performed using two different volumes
with and 3.9 fm on anisotropic clover lattices at
MeV with a lattice spacing of fm in the spatial direction and
in the temporal direction. Using multiple interpolating
operators from a non-displaced source, we present scattering information for
two ground state baryons in both the S=0 and S=2 channels. For S=0,
is extracted at two volumes, which lead to an extrapolated
scattering length of ,
indicating a weakly repulsive interaction. Additionally, for S=2, two separate
highly repulsive states are observed. We also present results on the
interactions of the excited strangeness -3, spin-1/2 states with the ground
spin-3/2 states for the spin-1 and spin-2 channels. Results for these
interactions are consistent with attractive behavior.Comment: 21 pages, 10 fig
Nuclear Reactions from Lattice QCD
One of the overarching goals of nuclear physics is to rigorously compute
properties of hadronic systems directly from the fundamental theory of strong
interactions, Quantum Chromodynamics (QCD). In particular, the hope is to
perform reliable calculations of nuclear reactions which will impact our
understanding of environments that occur during big bang nucleosynthesis, the
evolution of stars and supernovae, and within nuclear reactors and high
energy/density facilities. Such calculations, being truly ab initio, would
include all two-nucleon and three- nucleon (and higher) interactions in a
consistent manner. Currently, lattice QCD provides the only reliable option for
performing calculations of some of the low- energy hadronic observables. With
the aim of bridging the gap between lattice QCD and nuclear many-body physics,
the Institute for Nuclear Theory held a workshop on Nuclear Reactions from
Lattice QCD on March 2013. In this review article, we report on the topics
discussed in this workshop and the path planned to move forward in the upcoming
years.Comment: 35 pages, 13 figures, 1 table, review article for the "Nuclear
Reactions from Lattice QCD" workshop hosted by the Institute for Nuclear
Theory on March 2013; version 2 includes updated references and extended
discussion of previous wor
Two-Baryon Systems with Twisted Boundary Conditions
We explore the use of twisted boundary conditions in extracting the nucleon
mass and the binding energy of two-baryon systems, such as the deuteron, from
Lattice QCD calculations. Averaging the results of calculations performed with
periodic and anti-periodic boundary conditions imposed upon the light-quark
fields, or other pair-wise averages, improves the volume dependence of the
deuteron binding energy from ~exp(-kappa*L)/L to ~exp(-sqrt(2)kappa*L)/L.
However, a twist angle of pi/2 in each of the spatial directions improves the
volume dependence from ~exp(-kappa*L)/L to ~exp(-2kappa*L)/L. Twist averaging
the binding energy with a random sampling of twist angles improves the volume
dependence from ~exp^(-kappa*L)/L to ~exp(-2kappa*L)/L, but with a standard
deviation of ~exp(-kappa*L)/L, introducing a signal-to-noise issue in modest
lattice volumes. Using the experimentally determined phase shifts and mixing
angles, we determine the expected energies of the deuteron states over a range
of cubic lattice volumes for a selection of twisted boundary conditions.Comment: 20 pages, 3 figure
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