32,787 research outputs found
The "Unromantic Pictures" of Quantum Theory
I am concerned with two views of quantum mechanics that John S. Bell called
``unromantic'': spontaneous wave function collapse and Bohmian mechanics. I
discuss some of their merits and report about recent progress concerning
extensions to quantum field theory and relativity. In the last section, I
speculate about an extension of Bohmian mechanics to quantum gravity.Comment: 37 pages LaTeX, no figures; written for special volume of J. Phys. A
in honor of G.C. Ghirard
Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector
We present a physically motivated parameterization of the chiral-odd
generalized parton distributions. The parametrization is an extension of our
previous one in the chiral-even sector which was based on the reggeized diquark
model. While for chiral even generalized distributions a quantitative fit with
uncertainty estimation can be performed using deep inelastic scattering data,
nucleon electromagnetic, axial and pseudoscalar form factors measurements, and
all available deeply virtual Compton scattering data, the chiral-odd sector is
far less constrained. While awaiting the analysis of measurements on
pseudoscalar mesons exclusive electroproduction which are key for the
extraction of chiral odd GPDs, we worked out a connection between the
chiral-even and chiral-odd reduced helicity amplitudes using Parity
transformations. The connection works for a class of models including
two-components models. This relation allows us to estimate the size of the
various chiral odd contributions and it opens the way for future quantitative
fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.
Development of optimum clamp combinations for strap-down inertial measuring units with field replaceable sensors
Optimum clamp combinations for strap down inertial measuring units with field replaceable sensor
Are All Particles Identical?
We consider the possibility that all particles in the world are fundamentally
identical, i.e., belong to the same species. Different masses, charges, spins,
flavors, or colors then merely correspond to different quantum states of the
same particle, just as spin-up and spin-down do. The implications of this
viewpoint can be best appreciated within Bohmian mechanics, a precise
formulation of quantum mechanics with particle trajectories. The implementation
of this viewpoint in such a theory leads to trajectories different from those
of the usual formulation, and thus to a version of Bohmian mechanics that is
inequivalent to, though arguably empirically indistinguishable from, the usual
one. The mathematical core of this viewpoint is however rather independent of
the detailed dynamical scheme Bohmian mechanics provides, and it amounts to the
assertion that the configuration space for N particles, even N
``distinguishable particles,'' is the set of all N-point subsets of physical
3-space.Comment: 12 pages LaTeX, no figure
Shift Equivalence of Measures and the Intrinsic Structure of Shocks in the Asymmetric Simple Exclusion Process
We investigate properties of non-translation-invariant measures, describing
particle systems on \bbz, which are asymptotic to different translation
invariant measures on the left and on the right. Often the structure of the
transition region can only be observed from a point of view which is
random---in particular, configuration dependent. Two such measures will be
called shift equivalent if they differ only by the choice of such a viewpoint.
We introduce certain quantities, called translation sums, which, under some
auxiliary conditions, characterize the equivalence classes. Our prime example
is the asymmetric simple exclusion process, for which the measures in question
describe the microscopic structure of shocks. In this case we compute
explicitly the translation sums and find that shocks generated in different
ways---in particular, via initial conditions in an infinite system or by
boundary conditions in a finite system---are described by shift equivalent
measures. We show also that when the shock in the infinite system is observed
from the location of a second class particle, treating this particle either as
a first class particle or as an empty site leads to shift equivalent shock
measures.Comment: Plain TeX, 2 figures; [email protected], [email protected],
[email protected], [email protected]
Feynman's Path Integrals and Bohm's Particle Paths
Both Bohmian mechanics, a version of quantum mechanics with trajectories, and
Feynman's path integral formalism have something to do with particle paths in
space and time. The question thus arises how the two ideas relate to each
other. In short, the answer is, path integrals provide a re-formulation of
Schroedinger's equation, which is half of the defining equations of Bohmian
mechanics. I try to give a clear and concise description of the various aspects
of the situation.Comment: 4 pages LaTeX, no figures; v2 shortened a bi
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