2,358 research outputs found
Fluctuations, Ghosts, and the Cosmological Constant
For a large region of parameter space involving the cosmological constant and
mass parameters, we discuss fluctuating spacetime solutions that are
effectively Minkowskian on large time and distance scales. Rapid, small
amplitude oscillations in the scale factor have a frequency determined by the
size of a negative cosmological constant. A field with modes of negative energy
is required. If it is gravity that induces a coupling between the ghost-like
and normal fields, we find that this results in stochastic rather than unstable
behavior. The negative energy modes may also permit the existence of Lorentz
invariant fluctuating solutions of finite energy density. Finally we consider
higher derivative gravity theories and find oscillating metric solutions in
these theories without the addition of other fields.Comment: 15 pages, 1 figur
Classical Simulation of Quantum Fields II
We consider the classical time evolution of a real scalar field in 2
dimensional Minkowski space with a interaction. We compute the
spatial and temporal two-point correlation functions and extract the
renormalized mass of the interacting theory. We find our results are consistent
with the one- and two-loop quantum computation. We also perform Monte Carlo
simulations of the quantum theory and conclude that the classical scheme is
able to produce more accurate results with a fraction of the CPU time.Comment: 16 pages, 8 figures, now matches published versio
High temperature glass coatings for superalloys and refractory metals
New glasses are used as protective coatings on metals and alloys susceptible to oxidation at high temperatures in oxidizing atmospheres. Glasses are stable and solid at temperatures up to 1000 deg C, adhere well to metal surfaces, and are usable for metals with broad range of expansion coefficients
Construction of a topological charge on fuzzy S^2 x S^2 via Ginsparg-Wilson relation
We construct a topological charge of gauge field configurations on a fuzzy
S^2xS^2 by using a Dirac operator satisfying the Ginsparg-Wilson relation. The
topological charge defined on the fuzzy S^2xS^2 can be interpreted as a
noncommutative (or matrix) generalization of the 2nd Chern character on
S^2xS^2. We further calculate the number of chiral zero modes of the Dirac
operator in topologically nontrivial gauge configurations. Generalizations of
our formulation to fuzzy (S^2)^k are also discussed.Comment: 30 pages, typo corrected, version published in Phys.Rev.
Resistively detected nuclear magnetic resonance via a single InSb two-dimensional electron gas at high temperature
We report on the demonstration of the resistively detected nuclear magnetic
resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at
elevated temperatures up to 4 K. The RDNMR signal of 115In in the simplest
pseudospin quantum Hall ferromagnet triggered by a large direct current shows a
peak-dip line shape, where the nuclear relaxation time T1 at the peak and the
dip is different but almost temperature independent. The large Zeeman,
cyclotron, and exchange energy scales of the InSb 2DEG contribute to the
persistence of the RDNMR signal at high temperatures.Comment: 11pages,3figure
Resistively-detected NMR lineshapes in a quasi-one dimensional electron system
We observe variation in the resistively-detected nuclear magnetic resonance
(RDNMR) lineshapes in quantum Hall breakdown. The breakdown is locally occurred
in a gate-defined quantum point contact (QPC) region. Of particular interest is
the observation of a dispersive lineshape occured when the bulk 2D electron gas
(2DEG) is set to and the QPC filling factor to the vicinity
of , strikingly resemble the dispersive lineshape observed
on a 2D quantum Hall state. This previously unobserved lineshape in a QPC
points to simultaneous occurrence of two hyperfine-mediated spin flip-flop
processes within the QPC. Those events give rise to two different sets of
nuclei polarized in the opposite direction and positioned at a separate region
with different degree of electronic polarizations.Comment: Accepted as a rapid communication in PR
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