2,686 research outputs found
Quantum Monte Carlo Calculations for Carbon Nanotubes
We show how lattice Quantum Monte Carlo can be applied to the electronic
properties of carbon nanotubes in the presence of strong electron-electron
correlations. We employ the path-integral formalism and use methods developed
within the lattice QCD community for our numerical work. Our lattice
Hamiltonian is closely related to the hexagonal Hubbard model augmented by a
long-range electron-electron interaction. We apply our method to the
single-quasiparticle spectrum of the (3,3) armchair nanotube configuration, and
consider the effects of strong electron-electron correlations. Our approach is
equally applicable to other nanotubes, as well as to other carbon
nanostructures. We benchmark our Monte Carlo calculations against the two- and
four-site Hubbard models, where a direct numerical solution is feasible.Comment: 54 pages, 16 figures, published in Physical Review
Voronoi Particle Merging Algorithm for PIC Codes
We present a new particle-merging algorithm for the particle-in-cell method.
Based on the concept of the Voronoi diagram, the algorithm partitions the phase
space into smaller subsets, which consist of only particles that are in close
proximity in the phase space to each other. We show the performance of our
algorithm in the case of the two-stream instability and the magnetic shower.Comment: 11 figure
Three-fermion problems in optical lattices
We present exact results for the spectra of three fermionic atoms in a single
well of an optical lattice. For the three lowest hyperfine states of Li6 atoms,
we find a Borromean state across the region of the distinct pairwise Feshbach
resonances. For K40 atoms, nearby Feshbach resonances are known for two of the
pairs, and a bound three-body state develops towards the positive
scattering-length side. In addition, we study the sensitivity of our results to
atomic details. The predicted few-body phenomena can be realized in optical
lattices in the limit of low tunneling.Comment: 4 pages, 4 figures, minor changes, to appear in Phys. Rev. Let
Beyond-the-Standard-Model matrix elements with the gradient flow
At the Forschungszentrum Juelich (FZJ) we have started a long-term program
that aims to determine beyond-the-Standard-Model (BSM) matrix elements using
the gradient flow, and to understand the impact of BSM physics in nucleon and
nuclear observables. Using the gradient flow, we propose to calculate the QCD
component of key beyond the Standard Model (BSM) matrix elements related to
quark and strong theta CP violation and the strange content within the nucleon.
The former set of matrix elements impacts our understanding of Electric Dipole
Moments (EDMs) of nucleons and nuclei (a key signature of BSM physics), while
the latter contributes to elastic recoil of Dark Matter particles off nucleons
and nuclei. If successful, these results will lay the foundation for extraction
of BSM observables from future low-energy, high-intensity and high-accuracy
experimental measurements.Comment: 7 pages, 2 figures, presented at the 32nd International Symposium on
Lattice Field Theory (Lattice 2014). Correct version of proceedings.
Different wording of few paragraphs and different notation on few formulas.
Added 1 referenc
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
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
Two-Nucleon Systems in a Finite Volume: (II) 3S1-3D1 Coupled Channels and the Deuteron
The energy spectra of two nucleons in a cubic volume provide access to the
two phase shifts and one mixing angle that define the S-matrix in the 3S1-3D1
coupled channels containing the deuteron. With the aid of recently derived
energy quantization conditions for such systems, and the known scattering
parameters, these spectra are predicted for a range of volumes. It is found
that extractions of the infinite-volume deuteron binding energy and leading
scattering parameters, including the S-D mixing angle at the deuteron pole, are
possible from Lattice QCD calculations of two-nucleon systems with boosts of
|P| <= 2pi sqrt{3}/L in volumes with 10 fm <~ L <~ 14 fm. The viability of
extracting the asymptotic D/S ratio of the deuteron wavefunction from Lattice
QCD calculations is discussed.Comment: 31 pages, 17 figure
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