1,793 research outputs found
Low-momentum interactions for nuclei
We show how the renormalization group is used to construct a low-momentum
nucleon-nucleon interaction V_{low k}, which unifies all potential models used
in nuclear structure calculations. V_{low k} can be directly applied to the
nuclear shell model or to nucleonic matter without a G matrix resummation. It
is argued that V_{low k} parameterizes a high-order chiral effective field
theory two-nucleon force. We use cutoff dependence as a tool to assess the
error in the truncation of nuclear forces to two-nucleon interactions and
introduce a low-momentum three-nucleon force, which regulates A=3,4 binding
energies. The adjusted three-nucleon interaction is perturbative for small
cutoffs. In contrast to other precision interactions, the error due to missing
many-body forces can be estimated, when V_{low k} and the corresponding
three-nucleon force are used in nuclear structure calculations and the cutoff
is varied.Comment: 10 pages, 5 figures, talk at INT workshop on Nuclear Forces and the
Quantum Many-Body Problem, Seattle, October 200
Resonant relativistic corrections and the A_y problem
We study relativistic corrections to nuclear interactions caused by boosting
the two-nucleon interaction to a frame in which their total momentum does not
vanish. These corrections induce a change in the computed value of the
neutron-deuteron analyzing power A_y that is estimated using the plane-wave
impulse approximation. This allows a transparent analytical calculation that
demonstrates the significance of relativistic corrections. Faddeev calculations
are however needed to conclude on the A_y puzzle.Comment: 8 pages, 2 figures, minor addition, to appear in Phys. Rev.
Two-neutrino double electron capture on Xe based on an effective theory and the nuclear shell model
We study the two-neutrino double electron capture on Xe based on an
effective theory (ET) and large-scale shell model calculations, two modern
nuclear structure approaches that have been tested against Gamow-Teller and
double-beta decay data. In the ET, the low-energy constants are fit to electron
capture and transitions around xenon. For the nuclear shell model,
we use an interaction in a large configuration space that reproduces the
spectroscopy of nuclei in this mass region. For the dominant transition to the
Te ground state, we find half-lives y for the ET and y for the shell model. The ET uncertainty leads to
a half-life almost entirely consistent with present experimental limits and
largely within the reach of ongoing experiments. The shell model half-life
range overlaps with the ET, but extends less beyond current limits. Our
findings thus suggest that the two-neutrino double electron capture on
Xe has a good chance to be discovered by ongoing or future experiments.
In addition, we present results for the two-neutrino double electron capture to
excited states of Te.Comment: 5 pages, 2 figure
Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials
Chiral effective field theory is a framework to derive systematic nuclear
interactions. It is based on the symmetries of quantum chromodynamics and
includes long-range pion physics explicitly, while shorter-range physics is
expanded in a general operator basis. The number of low-energy couplings at a
particular order in the expansion can be reduced by exploiting the fact that
nucleons are fermions and therefore obey the Pauli exclusion principle. The
antisymmetry permits the selection of a subset of the allowed contact operators
at a given order. When local regulators are used for these short-range
interactions, however, this "Fierz rearrangement freedom" is violated. In this
paper, we investigate the impact of this violation at leading order (LO) in the
chiral expansion. We construct LO and next-to-leading order (NLO) potentials
for all possible LO-operator pairs and study their reproduction of phase
shifts, the He ground-state energy, and the neutron-matter energy at
different densities. We demonstrate that the Fierz rearrangement freedom is
partially restored at NLO where subleading contact interactions enter. We also
discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure
Shell-model phenomenology of low-momentum interactions
The first detailed comparison of the low-momentum interaction V_{low k} with
G matrices is presented. We use overlaps to measure quantitatively the
similarity of shell-model matrix elements for different cutoffs and oscillator
frequencies. Over a wide range, all sets of V_{low k} matrix elements can be
approximately obtained from a universal set by a simple scaling. In an
oscillator mean-field approach, V_{low k} reproduces satisfactorily many
features of the single-particle and single-hole spectra on closed-shell nuclei,
in particular through remarkably good splittings between spin-orbit partners on
top of harmonic oscillator closures. The main deficiencies of pure two-nucleon
interactions are associated with binding energies and with the failure to
ensure magicity for the extruder-intruder closures. Here, calculations
including three-nucleon interactions are most needed. V_{low k} makes it
possible to define directly a meaningful unperturbed monopole Hamiltonian, for
which the inclusion of three-nucleon forces is tractable.Comment: 5 pages, 4 figures, minor additions, to appear as Rapid Comm. in
Phys. Rev.
Quantum Monte Carlo Calculations of Light Nuclei Using Chiral Potentials
We present the first Green's function Monte Carlo calculations of light
nuclei with nuclear interactions derived from chiral effective field theory up
to next-to-next-to-leading order. Up to this order, the interactions can be
constructed in a local form and are therefore amenable to quantum Monte Carlo
calculations. We demonstrate a systematic improvement with each order for the
binding energies of and systems. We also carry out the first
few-body tests to study perturbative expansions of chiral potentials at
different orders, finding that higher-order corrections are more perturbative
for softer interactions. Our results confirm the necessity of a three-body
force for correct reproduction of experimental binding energies and radii, and
pave the way for studying few- and many-nucleon systems using quantum Monte
Carlo methods with chiral interactions.Comment: 5 pages, 3 figures, 4 tables. Updated references. Cosmetic changes to
figures, tables, and equations; added a sentence clarifying the
correspondence between our real-space cutoffs and momentum-space cutoffs.
Other sentences were reworded for clarit
Effective Nucleon-Nucleon Interaction and Fermi Liquid Theory
We present two novel relations between the quasiparticle interaction in
nuclear matter and the unique low momentum nucleon-nucleon interaction in
vacuum. These relations provide two independent constraints on the Fermi liquid
parameters of nuclear matter. Moreover, the new constraints define two
combinations of Fermi liquid parameters, which are invariant under the
renormalization group flow in the particle-hole channels. Using empirical
values for the spin-independent Fermi liquid parameters, we are able to compute
the major spin-dependent ones by imposing the new constraints as well as the
Pauli principle sum rules.Comment: 4 pages, 5 figures, in Proc. 11th International Conference on Recent
Progress in Many-Body Theories, Manchester, UK, July 9-13, 200
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