6,284 research outputs found
Extended Bose-Hubbard model with incompressible states at fractional numbers
The Bose-Hubbard model is extended to include nearest and far neighbor
interactions and is related to the fractional quantum Hall effect (FQHE). Both
models may be studied in optical lattices with quantum gases. The ground state
is calculated for the extended Bose-Hubbard model with strong repulsive
interactions (weak hopping). Incompressible Mott insulator states are found at
rational filling fractions compatible with the principal and secondary FQHE
filling fractions of the lowest Landau levels observed experimentally. It is
discussed to which extent these states at fractional filling survive or
undergoes a Mott insulator transition to a superfluid as hopping terms are
included.Comment: Revised version, to appear in PR
Gas of self-avoiding loops on the brickwork lattice
An exact calculation of the phase diagram for a loop gas model on the
brickwork lattice is presented. The model includes a bending energy. In the
dense limit, where all the lattice sites are occupied, a phase transition
occuring at an asymmetric Lifshitz tricritical point is observed as the
temperature associated with the bending energy is varied. Various critical
exponents are calculated. At lower densities, two lines of transitions (in the
Ising universality class) are observed, terminated by a tricritical point,
where there is a change in the modulation of the correlation function. To each
tricritical point an associated disorder line is found.Comment: 19 pages, 6 figures. to appear in J. Phys. A : Math. & Ge
Properties of the non-Gaussian fixed point in 4D compact U(1) lattice gauge theory
We examine selected properties of the gauge-ball spectrum and fermionic
variables in the vicinity of the recently discussed non-Gaussian fixed point of
4D compact U(1) lattice gauge theory within the quenched approximation.
Approaching the critical point from within the confinement phase, our data
support scaling of gauge-ball states in units of the string tension
square root. The analysis of the chiral condensate within the framework of a
scaling form for the equation of state suggests non mean-field values for the
magnetic exponents and .Comment: 73K postscript fil
Examination Feedback
This project focussed on exploring types of examination feedback. The project brought together key stakeholders from UPSU, students, academic and educational development staff. The aim was to consider perceptions, experiences, expectations and practical considerations of different feedback models to inform the development of an institutional wide examination feedback toolkit. Staff in two academic disciplines, Law and Sociology piloted different formats of examination feedback.TFA
Effective Field Theory of the Zero-Temperature Triangular-Lattice Antiferromagnet: A Monte Carlo Study
Using a Monte Carlo coarse-graining technique introduced by Binder et al., we
have explicitly constructed the continuum field theory for the zero-temperature
triangular Ising antiferromagnet. We verify the conjecture that this is a
gaussian theory of the height variable in the interface representation of the
spin model. We also measure the height-height correlation function and deduce
the stiffness constant. In addition, we investigate the nature of defect-defect
interactions at finite temperatures, and find that the two-dimensional Coulomb
gas scenario applies at low temperatures.Comment: 26 pages, 9 figure
Multichannel oscillations and relations between LSND, KARMEN and MiniBooNE, with and without CP violation
We show by examples that multichannel mixing can affect both the parameters
extracted from neutrino oscillation experiments, and that more general
conclusions derived by fitting the experimental data under the assumption that
only two channels are involved in the mixing. Implications for MiniBooNE are
noted and an example based on maximal CP violation displays profound
implications for the two data sets (muon-neutrino and muon-antineutrino) of
that experiment.Comment: 5 pages 4 figure
Architectural/Environmental Handbook for Extraterrestrial Design
Handbook on environmental and space utilization criteria for design of extraterrestrial manned spacecraft and shelter
Scaling of gauge balls and static potential in the confinement phase of the pure U(1) lattice gauge theory
We investigate the scaling behaviour of gauge-ball masses and static
potential in the pure U(1) lattice gauge theory on toroidal lattices. An
extended gauge field action is used with and -0.5. Gauge-ball correlation
functions with all possible lattice quantum numbers are calculated. Most
gauge-ball masses scale with the non-Gaussian exponent .
The gauge-ball mass scales with the Gaussian value in the investigated range of correlation lengths. The static potential is
examined with Sommer's method. The long range part scales consistently with
but the short range part tends to yield smaller values of . The
-function, having a UV stable zero, is obtained from the running
coupling. These results hold for both values, supporting universality.
Consequences for the continuum limit of the theory are discussed.Comment: Contribution to the Lattice 97 proceedings, LaTeX, 3 pages, 3 figure
Two-dimensional charge order in layered 2-1-4 perovskite oxides
Monte Carlo simulations are performed on the three-dimensional (3D) Ising
model with the 2-1-4 layered perovskite structure as a minimal model for
checkerboard charge ordering phenomena in layered perovskite oxides. Due to the
interlayer frustration, only 2D long-range order emerges with a finite
correlation length along the c axis. Critical exponents of the transition
change continuously as a function of the interlayer coupling constant. The
interlayer long-range Coulomb interaction decays exponentially and is
negligible even between the second-neighbor layers. Instead, monoclinic
distortion of a tetragonal unit cell lifts the macroscopic degeneracy to induce
a 3D charge ordering. The dimensionality of the charge order in
LaSrMnO is discussed from this viewpoint.Comment: 5 pages including 6 figures, with major changes including discussion
on charge ordering phenomena in layered perovskite oxide
Elementary excitations in the gapped phase of a frustrated S=1/2 spin ladder: from spinons to the Haldane triplet
We use the variational matrix-product ansatz to study elementary excitations
in the S=1/2 ladder with additional diagonal coupling, equivalent to a single
S=1/2 chain with alternating exchange and next-nearest neighbor interaction. In
absence of alternation the elementary excitation consists of two free S=1/2
particles ("spinons") which are solitons in the dimer order. When the
nearest-neighbor exchange alternates, the "spinons" are confined into one S=1
excitation being a soliton in the generalized string order. Variational results
are found to be in a qualitative agreement with the exact diagonalization data
for 24 spins. We argue that such an approach gives a reasonably good
description in a wide range of the model parameters.Comment: RevTeX, 13 pages, 11 embedded figures, uses psfig and multico
- …