45,663 research outputs found
Evolution of the single-hole spectral function across a quantum phase transition in the anisotropic-triangular-lattice antiferromagnet
We study the evolution of the single-hole spectral function when the ground
state of the anisotropic-triangular-lattice antiferromagnet changes from the
incommensurate magnetically-ordered phase to the spin-liquid state. In order to
describe both of the ground states on equal footing, we use the large-N
approach where the transition between these two phases can be obtained by
controlling the quantum fluctuations via an 'effective' spin magnitude. Adding
a hole into these ground states is described by a t-J type model in the
slave-fermion representation. Implications of our results to possible future
ARPES experiments on insulating frustrated magnets, especially CsCuCl,
are discussed.Comment: 8 pages, 7 figure
Induced Lorentz- and CPT-violating Chern-Simons term in QED: Fock-Schwinger proper time method
Using the Fock-Schwinger proper time method, we calculate the induced
Chern-Simons term arising from the Lorentz- and CPT-violating sector of quantum
electrodynamics with a term. Our
result to all orders in coincides with a recent linear-in- calculation
by Chaichian et al. [hep-th/0010129 v2]. The coincidence was pointed out by
Chung [Phys. Lett. {\bf B461} (1999) 138] and P\'{e}rez-Victoria [Phys. Rev.
Lett. {\bf 83} (1999) 2518] in the standard Feynman diagram calculation with
the nonperturbative-in- propagator.Comment: 11 pages, no figur
Lensed Arcs and Inner Structure of Abell 697
We present new optical observations of the z=0.282 cluster Abell 697 from the
Keck II telescope. Images show an unusual disturbed structure in the cD halo
and a previously unknown faint gravitational lens arc. A spectrum of the arc
did not yield a redshift, but its spectrum and colors suggest it lies at z>1.3.
We construct models to reproduce the arc that show the potential is likely to
be highly elliptical. We suggest that this cluster may have undergone a recent
merger and is in the process of forming its cD galaxy. Analysis of X-ray data
from ROSAT and ASCA suggests that the merging process is sufficiently advanced
that the gas in the cluster has relaxed, and A697 lies near the L_x-T_x
relation for normal clusters.Comment: LaTeX; 12 pages, 3 figures, submitted to ApJ Letter
High Density Preheating Effects on Q-ball Decays and MSSM Inflation
Non-perturbative preheating decay of post-inflationary condensates often
results in a high density, low momenta, non-thermal gas. In the case where the
non-perturbative classical evolution also leads to Q-balls, this effect shields
them from instant dissociation, and may radically change the thermal history of
the universe. For example, in a large class of inflationary scenarios,
motivated by the MSSM and its embedding in string theory, the reheat
temperature changes by a multiplicative factor of .Comment: 4 page
Phase equilibrium modeling for high temperature metallization on GaAs solar cells
Recent trends in performance specifications and functional requirements have brought about the need for high temperature metallization technology to be developed for survivable DOD space systems and to enhance solar cell reliability. The temperature constitution phase diagrams of selected binary and ternary systems were reviewed to determine the temperature and type of phase transformation present in the alloy systems. Of paramount interest are the liquid-solid and solid-solid transformations. Data are being utilized to aid in the selection of electrical contact materials to gallium arsenide solar cells. Published data on the phase diagrams for binary systems is readily available. However, information for ternary systems is limited. A computer model is being developed which will enable the phase equilibrium predictions for ternary systems where experimental data is lacking
Adjacency labeling schemes and induced-universal graphs
We describe a way of assigning labels to the vertices of any undirected graph
on up to vertices, each composed of bits, such that given the
labels of two vertices, and no other information regarding the graph, it is
possible to decide whether or not the vertices are adjacent in the graph. This
is optimal, up to an additive constant, and constitutes the first improvement
in almost 50 years of an bound of Moon. As a consequence, we
obtain an induced-universal graph for -vertex graphs containing only
vertices, which is optimal up to a multiplicative constant,
solving an open problem of Vizing from 1968. We obtain similar tight results
for directed graphs, tournaments and bipartite graphs
Calculation of reduced density matrices from correlation functions
It is shown that for solvable fermionic and bosonic lattice systems, the
reduced density matrices can be determined from the properties of the
correlation functions. This provides the simplest way to these quantities which
are used in the density-matrix renormalization group method.Comment: 4 page
Random Vibrational Networks and Renormalization Group
We consider the properties of vibrational dynamics on random networks, with
random masses and spring constants. The localization properties of the
eigenstates contrast greatly with the Laplacian case on these networks. We
introduce several real-space renormalization techniques which can be used to
describe this dynamics on general networks, drawing on strong disorder
techniques developed for regular lattices. The renormalization group is capable
of elucidating the localization properties, and provides, even for specific
network instances, a fast approximation technique for determining the spectra
which compares well with exact results.Comment: 4 pages, 3 figure
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