22,618 research outputs found
Exact Nonperturbative Unitary Amplitudes for 1->N Transitions
I present an extension to arbitrary N of a previously proposed field
theoretic model, in which unitary amplitudes for processes were
obtained. The Born amplitude in this extension has the behavior
expected in a bosonic field theory. Unitarity
is violated when , or when Numerical
solutions of the coupled Schr\"odinger equations shows that for weak coupling
and a large range of N>\ncrit, the exact unitary amplitude is reasonably fit
by a factorized expression |A(1->N)| \sim (0.73 /N) \cdot \exp{(-0.025/\g2)}.
The very small size of the coefficient 1/\g2 , indicative of a very weak
exponential suppression, is not in accord with standard discussions based on
saddle point analysis, which give a coefficient The weak dependence
on could have experimental implications in theories where the exponential
suppression is weak (as in this model). Non-perturbative contributions to
few-point correlation functions in this theory would arise at order $K\ \simeq\
\left((0.05/\g2)+ 2\ ln{N}\right)/ \ ln{(1/\g2)}\g2.$Comment: 11 pages, 3 figures (not included
Evidence of Skyrmion excitations about in n-Modulation Doped Single Quantum Wells by Inter-band Optical Transmission
We observe a dramatic reduction in the degree of spin-polarization of a
two-dimensional electron gas in a magnetic field when the Fermi energy moves
off the mid-point of the spin-gap of the lowest Landau level, . This
rapid decay of spin alignment to an unpolarized state occurs over small changes
to both higher and lower magnetic field. The degree of electron spin
polarization as a function of is measured through the magneto-absorption
spectra which distinguish the occupancy of the two electron spin states. The
data provide experimental evidence for the presence of Skyrmion excitations
where exchange energy dominates Zeeman energy in the integer quantum Hall
regime at
Dielectric cure monitoring: Preliminary studies
Preliminary studies have been conducted on two types of dielectric cure monitoring systems employing both epoxy resins and phenolic composites. An Audrey System was used for 23 cure monitoring runs with very limited success. Nine complete cure monitoring runs have been investigated using a Micromet System. Two additional measurements were performed to investigate the Micromet's sensitivity to water absorption in a post-cure carbon-phenolic material. While further work is needed to determine data significance, the Micromet system appears to show promise as a feedback control device during processing
The non-metallic materials sample array
The Non-Metallic Materials Sample Array (MSA) was flown as verification flight instrumentation (VFI) on both Spacelab 1 (SL-1) and Spacelab 2 (SL-2). The basis for materials selection was either previous flight history or probable flight suitability based upon analysis. The observed changes in the optical properties of the exposed materials are, in general, quite minimal; however, this data represents the short exposure of two Space Shuttle missions, and no attempt should be made to extrapolate the long-term exposure. The MSA was in orbit for 10 days at approximately 240 km on SL-1 and for 7 days at approximately 315 km on SL-2. The array was exposed to the solar flux for only a portion of the time in orbit
Statistics of Oscillator Strengths in Chaotic Systems
The statistical description of oscillator strengths for systems like hydrogen
in a magnetic field is developed by using the supermatrix nonlinear
-model. The correlator of oscillator strengths is found to have a
universal parametric and frequency dependence, and its analytical expression is
given. This universal expression applies to quantum chaotic systems with the
same generality as Wigner-Dyson statistics.Comment: 11 pages, REVTeX3+epsf, two EPS figures. Replaced by the published
version. Minor changes
Lattice-corrected strain-induced vector potentials in graphene
The electronic implications of strain in graphene can be captured at low
energies by means of pseudovector potentials which can give rise to
pseudomagnetic fields. These strain-induced vector potentials arise from the
local perturbation to the electronic hopping amplitudes in a tight-binding
framework. Here we complete the standard description of the strain-induced
vector potential, which accounts only for the hopping perturbation, with the
explicit inclusion of the lattice deformations or, equivalently, the
deformation of the Brillouin zone. These corrections are linear in strain and
are different at each of the strained, inequivalent Dirac points, and hence are
equally necessary to identify the precise magnitude of the vector potential.
This effect can be relevant in scenarios of inhomogeneous strain profiles,
where electronic motion depends on the amount of overlap among the local Fermi
surfaces. In particular, it affects the pseudomagnetic field distribution
induced by inhomogeneous strain configurations, and can lead to new
opportunities in tailoring the optimal strain fields for certain desired
functionalities.Comment: Errata for version
Exciton mediated one phonon resonant Raman scattering from one-dimensional systems
We use the Kramers-Heisenberg approach to derive a general expression for the
resonant Raman scattering cross section from a one-dimensional (1D) system
explicitly accounting for excitonic effects. The result should prove useful for
analyzing the Raman resonance excitation profile lineshapes for a variety of 1D
systems including carbon nanotubes and semiconductor quantum wires. We apply
this formalism to a simple 1D model system to illustrate the similarities and
differences between the free electron and correlated electron-hole theories.Comment: 10 pages, 6 figure
Some Properties of Amplitudes at Multi Boson Thresholds in Spontaneously Broken Scalar Theory
It is shown that in a theory of one real scalar field with
spontaneous breaking of symmetry a calculation of the amplitudes of production
by a virtual field of on-mass-shell bosons all being exactly at rest
is equivalent in any order of the loop expansion to a Euclidean space
calculation of the mean field of a kink-type configuration. Using this
equivalence it is found that all the amplitudes have no absorptive
part at the thresholds to any order of perturbation theory. This implies
non-trivial relations between multi-boson threshold production amplitudes. In
particular the on-mass-shell amplitude of the process should vanish
at the threshold in all loops. It is also shown that the factor in the amplitudes at the threshold is not eliminated by loop effects.Comment: 11 pages including 3 figures, LaTeX, TPI-MINN-92/61-
Weak Gravitational Flexion
Flexion is the significant third-order weak gravitational lensing effect
responsible for the weakly skewed and arc-like appearance of lensed galaxies.
Here we demonstrate how flexion measurements can be used to measure galaxy halo
density profiles and large-scale structure on non-linear scales, via
galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation
functions. We describe the origin of gravitational flexion, and discuss its
four components, two of which are first described here. We also introduce an
efficient complex formalism for all orders of lensing distortion. We proceed to
examine the flexion predictions for galaxy-galaxy lensing, examining isothermal
sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric
and elliptical cases. We show that in combination with shear we can precisely
measure galaxy masses and NFW halo concentrations. We also show how flexion
measurements can be used to reconstruct mass maps in 2-D projection on the sky,
and in 3-D in combination with redshift data. Finally, we examine the
predictions for cosmic flexion, including convergence-flexion
cross-correlations, and find that the signal is an effective probe of structure
on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA
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