3,148 research outputs found
Gluon Chain Model of the Confining Force
We develop a picture of the QCD string as a chain of constituent gluons,
bound by attractive nearest-neighbor forces which may be treated
perturbatively. This picture accounts for both Casimir scaling at large N, and
the asymptotic center dependence of the static quark potential. We discuss the
relevance, to the gluon-chain picture, of recent three-loop results for the
static quark potential. A variational framework is presented for computing the
minimal energy and wavefunction of a long gluon chain, which enables us to
derive both the logarithmic broadening of the QCD flux tube (``roughening''),
and the existence of a Luscher -c/R term in the potential.Comment: 25 pages, 5 figures, latex2
Electron Beam Ion Sources
Electron beam ion sources (EBISs) are ion sources that work based on the
principle of electron impact ionization, allowing the production of very highly
charged ions. The ions produced can be extracted as a DC ion beam as well as
ion pulses of different time structures. In comparison to most of the other
known ion sources, EBISs feature ion beams with very good beam emittances and a
low energy spread. Furthermore, EBISs are excellent sources of photons (X-rays,
ultraviolet, extreme ultraviolet, visible light) from highly charged ions. This
chapter gives an overview of EBIS physics, the principle of operation, and the
known technical solutions. Using examples, the performance of EBISs as well as
their applications in various fields of basic research, technology and medicine
are discussed.Comment: 37 pages, contribution to the CAS-CERN Accelerator School: Ion
Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Baile
Defining the Force between Separated Sources on a Light Front
The Newtonian character of gauge theories on a light front requires that the
longitudinal momentum P^+, which plays the role of Newtonian mass, be
conserved. This requirement conflicts with the standard definition of the force
between two sources in terms of the minimal energy of quantum gauge fields in
the presence of a quark and anti-quark pinned to points separated by a distance
R. We propose that, on a light front, the force be defined by minimizing the
energy of gauge fields in the presence of a quark and an anti-quark pinned to
lines (1-branes) oriented in the longitudinal direction singled out by the
light front and separated by a transverse distance R. Such sources will have a
limited 1+1 dimensional dynamics. We study this proposal for weak coupling
gauge theories by showing how it leads to the Coulomb force law. For QCD we
also show how asymptotic freedom emerges by evaluating the S-matrix through one
loop for the scattering of a particle in the N_c representation of color
SU(N_c) on a 1-brane by a particle in the \bar N_c representation of color on a
parallel 1-brane separated from the first by a distance R<<1/Lambda_{QCD}.
Potential applications to the problem of confinement on a light front are
discussed.Comment: LaTeX, 15 pages, 12 figures; minor typos corrected; numerical
correction in equation 3.
Universality and Clustering in 1+1 Dimensional Superstring-Bit Models
We construct a 1+1 dimensional superstring-bit model for D=3 Type IIB
superstring. This low dimension model escapes the problems encountered in
higher dimension models: (1) It possesses full Galilean supersymmetry; (2) For
noninteracting polymers of bits, the exactly soluble linear superpotential
describing bit interactions is in a large universality class of superpotentials
which includes ones bounded at spatial infinity; (3) The latter are used to
construct a superstring-bit model with the clustering properties needed to
define an -matrix for closed polymers of superstring-bits.Comment: 11 pages, Latex documen
Bag Model for a Link in a Closed Gluonic Chain
The large limit of Yang-Mills gauge theory is the dynamics of a closed
gluonic chain, but this fact does not obviate the inherently strong coupling
nature of the dynamical problem. However, we suggest that a single link in such
a chain might be reasonably described in the quasi-perturbative language of
gluons and their interactions. To implement this idea, we use the MIT bag to
model the physics of a nearest neighbor bond.Comment: 10 pages, LaTe
The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
We present the results of polarimetric ( band) and multicolor photometric
() observations of the blazar AO 0235+16 during an outburst in 2006
December. The data reveal a short timescale of variability (several hours),
which increases from optical to near-IR wavelengths; even shorter variations
are detected in polarization. The flux density correlates with the degree of
polarization, and at maximum degree of polarization the electric vector tends
to align with the parsec-scale jet direction. We find that a variable component
with a steady power-law spectral energy distribution and very high optical
polarization (30-50%) is responsible for the variability. We interpret these
properties of the blazar withina model of a transverse shock propagating down
the jet. In this case a small change in the viewing angle of the jet, by
, and a decrease in the shocked plasma compression by a factor of
1.5 are sufficient to account for the variability.Comment: 22 pages, 8 figures, accepted for Ap
Subcritical String and Large N QCD
We pursue the possibility of using subcritical string theory in 4 space-time
dimensions to establish a string dual for large N QCD. In particular we study
the even G-parity sector of the 4 dimensional Neveu-Schwarz dual resonance
model as the natural candidate for this string theory. Our point of view is
that the open string dynamics given by this model will {\it determine} the
appropriate subcritical closed string theory, a tree level background of which
should describe the sum of planar multi-loop open string diagrams. We examine
the one loop open string diagram, which contains information about the closed
string spectrum at weak coupling. Higher loop open string diagrams will be
needed to determine closed string interactions. We also analyze the field
theory limit of the one loop open string diagram and recover the correct
running coupling behavior of the limiting gauge theory.Comment: 18 pages, 2 figures, error in eqs 46 and 47 correcte
Fusion of neurohypophyseal membranes in vitro
Freeze cleaving electron microscopy has shown that fusion of isolated secretory vesicles from bovine neurohypophyses was induced by Ca
2+ in micromolar concentrations. Mg
2+ and Sr
2+ were ineffective. Mg
2+ inhibited Ca
2+-induced fusion.
In suspensions containing secretory vesicles as well as sheets of cell membrane, release of vasopressin parallel to intervesicular fusion of secretory vesicles with sheets of cell membrane was observed after exposure to Ca
2+. Mg
2+ and Sr
2+ were ineffective in replacing Ca
2+ as trigger for fusion or vasopressin release.
Intervesicular fusion and exocytotic profiles were observed when isolated neurohypophyses or neurosecretosome were exposed to cold
Covariant And Local Field Theory On The World Sheet
In earlier work, using the light cone picture, a world sheet field theory
that sums planar phi^3 graphs was constructed and developed. Since this theory
is both non-local and not explicitly Lorentz invariant, it is desirable to have
a covariant and local alternative. In this paper, we construct such a covariant
and local world sheet theory, and show that it is equivalent to the original
non-covariant version.Comment: 22 pages,3 figures, typos and eqs.(11) and (63) are correcte
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