36 research outputs found
Collective Modes in a Symmetry-Broken Phase: Antiferromagnetically Correlated Quantum Wells
We investigate the intersubband spin-density-excitation spectrum of a double
quantum well in a low-density symmetry-broken phase with interwell
antiferromagnetic correlations. This spectrum is related to the intensity
measured in depolarized inelastic light scattering (ILS) experiments and
therefore provides a means of empirically identifying the antiferromagnetic
phase. Our computations reveal the existence of two collective modes, a damped
Nambu-Goldstone (NG) mode arising from the broken spin symmetry and an undamped
optical mode. Since the NG mode contains most of the spectral weight, ILS
experiments will need to examine the low-frequency response for signatures of
the antiferromagnetic phase.Comment: 4 pages, REVTEX with psfig macro, 4 figure
Multiple bound states in scissor-shaped waveguides
We study bound states of the two-dimensional Helmholtz equations with
Dirichlet boundary conditions in an open geometry given by two straight leads
of the same width which cross at an angle . Such a four-terminal
junction with a tunable can realized experimentally if a right-angle
structure is filled by a ferrite. It is known that for there is
one proper bound state and one eigenvalue embedded in the continuum. We show
that the number of eigenvalues becomes larger with increasing asymmetry and the
bound-state energies are increasing as functions of in the interval
. Moreover, states which are sufficiently strongly bent exist in
pairs with a small energy difference and opposite parities. Finally, we discuss
how with increasing the bound states transform into the quasi-bound
states with a complex wave vector.Comment: 6 pages, 6 figure
Effective field theory
I give a brief review of effective field theory, disscussing the contribution
of Feza G\"ursey in particular and focusing on the literature I am most
familiar with.Comment: 17 pages, no figs, macros appended, plain te
Topological Defects and CMB anisotropies : Are the predictions reliable ?
We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.Comment: 14 pages, accepted for publication in PR
Jorge A. Swieca's contributions to quantum field theory in the 60s and 70s and their relevance in present research
After revisiting some high points of particle physics and QFT of the two
decades from 1960 to 1980, I comment on the work by Jorge Andre Swieca. I
explain how it fits into the quantum field theory during these two decades and
draw attention to its relevance to the ongoing particle physics research. A
particular aim of this article is to direct thr readers mindfulness to the
relevance of what at the time of Swieca was called "the Schwinger Higgs
screening mechanism". which, together with recent ideas which generalize the
concept of gauge theories, has all the ingredients to revolutionize the issue
of gauge theories and the standard model.Comment: 49 pages, expansion and actualization of text, improvement of
formulations and addition of many references to be published in EPJH -
Historical Perspectives on Contemporary Physic
Noncommutative Fluids
We review the connection between noncommutative gauge theory, matrix models
and fluid mechanical systems. The noncommutative Chern-Simons description of
the quantum Hall effect and bosonization of collective fermion states are used
as specific examples.Comment: To appear in "Seminaire Poincare X", Institut Henri Poincare, Paris;
references adde
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Relaxation of thermal mismatch in discontinuously reinforced composites
We have measured the dislocation density vol % and thermal residual elastic strain in NiAl matrices of 20 vol % Al{sub 2}O{sub 3} discontinuously-reinforced composites. As the size of the reinforcement increases the average dislocation density increases, and the corresponding thermal residual elastic strains decrease. The changes with respect to particle size in the dislocation density and residual strain can neither be explained by continuum theory nor by dislocation mechanics for homogeneous medium. A previously developed model (that satisfactorily describes the SiC/Al system) suggests that the misfit dislocation density decreases with increase in reinforcement size but this disagrees wit the current Al{sub 2}O{sub 3}/NiAl results. A new model is proposed to describe low-symmetry intermetallics, which are constrained in their ability to relax thermal mismatch because of a paucity of independent slip systems. The results are discussed in the context of continuum mechanics using finite element analyses and crystal plasticity