37 research outputs found
Lattice formulation of (2,2) supersymmetric gauge theories with matter fields
We construct lattice actions for a variety of (2,2) supersymmetric gauge
theories in two dimensions with matter fields interacting via a superpotential.Comment: 13 pages, 2 figures. Appendix added, references updated, typos fixe
A new approach for studying large numbers of fermions in the unitary regime
A novel lattice approach is presented for studying systems comprising a large number of interacting nonrelativistic fermions. The construction is ideally suited for numerical study of fermions near unitarity-a strongly coupled regime corresponding to the two-particle s-wave scattering phase shift δ0 = ≠/2. Such systems may be achieved experimentally with trapped atoms, and provide a starting point for an effective field theory description of nuclear physics. We discuss the construction of our lattice theory, which allows us to study systems of up to (but by no means limited to) 38 fermions with high accuracy and modest computational resources, and offer an overview of several applications of the technique. A more detailed discussion of applications and simulation results will be described in companion proceedings by A. N. N. and J-W. L
Listening to noise
We show how sign problems in simulations of many-body systems can manifest themselves in the form of heavy-tailed correlator distributions, similar to what is seen in electron propagation through disordered media. We propose an alternative statistical approach for extracting ground state energies in such systems, illustrating the method with a toy model and with lattice data for unitary fermions
Two-dimensional N=(2,2) super Yang-Mills theory on computer
We carry out preliminary numerical study of Sugino's lattice formulation
\cite{Sugino:2004qd,Sugino:2004qdf} of the two-dimensional
super Yang-Mills theory (2d SYM) with the gauge group
\SU(2). The effect of dynamical fermions is included by re-weighting a
quenched ensemble by the pfaffian factor. It appears that the complex phase of
the pfaffian due to lattice artifacts and flat directions of the classical
potential are not problematic in Monte Carlo simulation. Various one-point
supersymmetric Ward-Takahashi (WT) identities are examined for lattice spacings
up to with the fixed physical lattice size , where
denotes the gauge coupling constant in two dimensions. WT identities implied by
an exact fermionic symmetry of the formulation are confirmed in fair accuracy
and, for most of these identities, the quantum effect of dynamical fermions is
clearly observed. For WT identities expected only in the continuum limit, the
results seem to be consistent with the behavior expected from supersymmetry,
although we do not see clear distintion from the quenched simulation. We
measure also the expectation values of renormalized gauge-invariant bi-linear
operators of scalar fields.Comment: 24 pages, 10 figures, the distribution of the complex phase of the
pffafian is also measured, the final version to appear in JHE
Deformed matrix models, supersymmetric lattice twists and N=1/4 supersymmetry
A manifestly supersymmetric nonperturbative matrix regularization for a
twisted version of N=(8,8) theory on a curved background (a two-sphere) is
constructed. Both continuum and the matrix regularization respect four exact
scalar supersymmetries under a twisted version of the supersymmetry algebra. We
then discuss a succinct Q=1 deformed matrix model regularization of N=4 SYM in
d=4, which is equivalent to a non-commutative orbifold lattice
formulation. Motivated by recent progress in supersymmetric lattices, we also
propose a N=1/4 supersymmetry preserving deformation of N=4 SYM theory on
. In this class of N=1/4 theories, both the regularized and continuum
theory respect the same set of (scalar) supersymmetry. By using the equivalence
of the deformed matrix models with the lattice formulations, we give a very
simple physical argument on why the exact lattice supersymmetry must be a
subset of scalar subalgebra. This argument disagrees with the recent claims of
the link approach, for which we give a new interpretation.Comment: 47 pages, 3 figure
Stripes, Pseudogaps, and Van Hove Nesting in the Three-band tJ Model
Slave boson calculations have been carried out in the three-band tJ model for
the high-T_c cuprates, with the inclusion of coupling to oxygen breathing mode
phonons. Phonon-induced Van Hove nesting leads to a phase separation between a
hole-doped domain and a (magnetic) domain near half filling, with long-range
Coulomb forces limiting the separation to a nanoscopic scale. Strong
correlation effects pin the Fermi level close to, but not precisely at the Van
Hove singularity (VHS), which can enhance the tendency to phase separation. The
resulting dispersions have been calculated, both in the uniform phases and in
the phase separated regime. In the latter case, distinctly different
dispersions are found for large, random domains and for regular (static)
striped arrays, and a hypothetical form is presented for dynamic striped
arrays. The doping dependence of the latter is found to provide an excellent
description of photoemission and thermodynamic experiments on pseudogap
formation in underdoped cuprates. In particular, the multiplicity of observed
gaps is explained as a combination of flux phase plus charge density wave (CDW)
gaps along with a superconducting gap. The largest gap is associated with VHS
nesting. The apparent smooth evolution of this gap with doping masks a
crossover from CDW-like effects near optimal doping to magnetic effects (flux
phase) near half filling. A crossover from large Fermi surface to hole pockets
with increased underdoping is found. In the weakly overdoped regime, the CDW
undergoes a quantum phase transition (), which could be obscured
by phase separation.Comment: 15 pages, Latex, 18 PS figures Corrects a sign error: major changes,
esp. in Sect. 3, Figs 1-4,6 replace
Tight-binding parameters for charge transfer along DNA
We systematically examine all the tight-binding parameters pertinent to
charge transfer along DNA. The molecular structure of the four DNA bases
(adenine, thymine, cytosine, and guanine) is investigated by using the linear
combination of atomic orbitals method with a recently introduced
parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are
discussed and then used for calculating the corresponding wavefunctions of the
two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO
and LUMO energies of the bases are in good agreement with available
experimental values. Our results are then used for estimating the complete set
of charge transfer parameters between neighboring bases and also between
successive base-pairs, considering all possible combinations between them, for
both electrons and holes. The calculated microscopic quantities can be used in
mesoscopic theoretical models of electron or hole transfer along the DNA double
helix, as they provide the necessary parameters for a tight-binding
phenomenological description based on the molecular overlap. We find that
usually the hopping parameters for holes are higher in magnitude compared to
the ones for electrons, which probably indicates that hole transport along DNA
is more favorable than electron transport. Our findings are also compared with
existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table
Blood chemistry profile of Surubim hybrid fish (Pseudoplatystoma reticulatum X P. corruscans) raised in different stocking densities
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Radiation dose to construction workers at operating nuclear power plant sites. Volume 2. Appendices A--F. Final report, September 1975--September 1978
These appendices contain the dosimetry procedures and details of the personnel and environmental dosimeters used for the Radiation Dose to Construction Workers at Operating Nuclear Power Plant Sites Study. A printout of the computer codes used to analyze dosimeter data is included along with all the raw data obtained. Appendices C through F contain computer output and log-normal plots of dosimetry data for environmental location and construction worker groups