10,286 research outputs found
Closed String Amplitudes from Gauge Fixed String Field Theory
Closed string diagrams are derived from cubic open string field theory using
a gauge fixed kinetic operator. The basic idea is to use a string propagator
that does not generate a boundary to the world sheet. Using this propagator and
the closed string vertex, the moduli space of closed string surfaces is
covered, so closed string scattering amplitudes should be reproduced. This
kinetic operator could be a gauge fixed form of the string field theory action
around the closed string vacuum.Comment: 10 pages, revtex, 3 figures. Discussion on the covering of moduli
expanded, version to appear in PR
A survey of Applied Psychological Services' models of the human operator
A historical perspective is presented in terms of the major features and status of two families of computer simulation models in which the human operator plays the primary role. Both task oriented and message oriented models are included. Two other recent efforts are summarized which deal with visual information processing. They involve not whole model development but a family of subroutines customized to add the human aspects to existing models. A global diagram of the generalized model development/validation process is presented and related to 15 criteria for model evaluation
Super Multi-Instantons in Conformal Chiral Superspace
We reformulate self-dual supersymmetric theories directly in conformal chiral
superspace, where superconformal invariance is manifest. The superspace can be
interpreted as the generalization of the usual Atiyah-Drinfel'd-Hitchin-Manin
twistors (the quaternionic projective line), the real projective light-cone in
six dimensions, or harmonic superspace, but can be reduced immediately to
four-dimensional chiral superspace. As an example, we give the 't Hooft and
ADHM multi-instanton constructions for self-dual super Yang-Mills theory. In
both cases, all the parameters are represented as a single, irreducible,
constant tensor.Comment: 21 pg., uuencoded compressed postscript file (twist.ps.Z.uu), other
formats (.dvi, .ps, .ps.Z, 8-bit .tex) available at
http://insti.physics.sunysb.edu/~siegel/preprints or at
ftp://max.physics.sunysb.edu/preprints/siege
Proximity effect model of ultra-narrow NbN strips
We show that narrow superconducting strips in superconducting (S) and normal
(N) states are universally described by the model presenting them as lateral
NSN proximity systems in which the superconducting central band is sandwiched
between damaged edge-bands with suppressed superconductivity.The width of the
superconducting band was experimentally determined from the value of magnetic
field at which the band transits from the Meissner state to the static vortex
state. Systematic experimental study of 4.9 nm thick NbN strips with widths in
the interval from 50 nm to 20 m, which are all smaller than the Pearl's
length, demonstrates gradual evolution of the temperature dependence of the
critical current with the change of the strip width
The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
Photometry with HST's ACS reveals that the subgiant branch (SGB) of the
globular cluster NGC 1851 splits into two well-defined branches. If the split
is due only to an age effect, the two SGBs would imply two star formation
episodes separated by 1 Gyr. We discuss other anomalies in NGC 1851
which could be interpreted in terms of a double stellar population. Finally, we
compare the case of NGC 1851 with the other two globulars known to host
multiple stellar populations, and show that all three clusters differ in
several important respects.Comment: 22 pages, 7 figures, accepted for pubblication on Ap
Considerations on Super Poincare Algebras and their Extensions to Simple Superalgebras
We consider simple superalgebras which are a supersymmetric extension of
\fspin(s,t) in the cases where the number of odd generators does not exceed
64. All of them contain a super Poincar\'e algebra as a contraction and another
as a subalgebra. Because of the contraction property, some of these algebras
can be interpreted as de Sitter or anti de Sitter superalgebras. However, the
number of odd generators present in the contraction is not always minimal due
to the different splitting properties of the spinor representations under a
subalgebra. We consider the general case, with arbitrary dimension and
signature, and examine in detail particular examples with physical implications
in dimensions and .Comment: 16 pages, AMS-LaTeX. Version to appear in the Reviews in Mathematical
Physic
Constraining the History of the Sagittarius Dwarf Galaxy Using Observations of its Tidal Debris
We present a comparison of semi-analytic models of the phase-space structure
of tidal debris with observations of stars associated with the Sagittarius
dwarf galaxy (Sgr). We find that many features in the data can be explained by
these models. The properties of stars 10-15 degrees away from the center of Sgr
--- in particular, the orientation of material perpendicular to Sgr's orbit
(c.f. Alard 1996) and the kink in the velocity gradient (Ibata et al 1997) ---
are consistent with those expected for unbound material stripped during the
most recent pericentric passage ~50 Myrs ago. The break in the slope of the
surface density seen by Mateo, Olszewski & Morrison (1998) at ~ b=-35 can be
understood as marking the end of this material. However, the detections beyond
this point are unlikely to represent debris in a trailing streamer, torn from
Sgr during the immediately preceding passage ~0.7 Gyrs ago, but are more
plausibly explained by a leading streamer of material that was lost more that 1
Gyr ago and has wrapped all the way around the Galaxy. The observations
reported in Majewski et al (1999) also support this hypothesis. We determine
debris models with these properties on orbits that are consistent with the
currently known positions and velocities of Sgr in Galactic potentials with
halo components that have circular velocities v_circ=140-200 km/s. The best
match to the data is obtained in models where Sgr currently has a mass of ~10^9
M_sun and has orbited the Galaxy for at least the last 1 Gyr, during which time
it has reduced its mass by a factor of 2-3, or luminosity by an amount
equivalent to ~10% of the total luminosity of the Galactic halo. These numbers
suggest that Sgr is rapidly disrupting and unlikely to survive beyond a few
more pericentric passages.Comment: 19 pages, 5 figures, accepted to Astronomical Journa
N=1 SUPER-P-BRANES in twistor-like Lorentz harmonic formulation
Unique twistor--like Lorentz harmonic formulation for all N=1 supersymmetric
extended objects (super-p-branes) moving in the space--time of arbitrary
dimension D (admissible for given ) are suggested. The equations of motion
are derived, explicit form of the \kappa-symmetry transformations is presented
and the classical equivalence to the standard formulation is proved.
The cases with minimal world--sheet dimensions , namely of D=10
heterotic string and D=11 supermembrane, are considered in details. In
particular, the explicit form of irreducible \kappa-symmetry transformations
for D=11 supermembrane is derived.Comment: (revized: minor changes, which was nesessary because previous version
cannot be read LATEX byond Padova University), 24 pages, LATEX ,
DEPD/94/TH/3
Why Don't We Have a Covariant Superstring Field Theory?
This talk deals with the old problem of formulatingn a covariant quantum
theory of superstrings, ``covariant'' here meaning having manifest Lorentz
symmetry and supersymmetry. The advantages and disadvantages of several
quantization methods are reviewed. Special emphasis is put on the approaches
using twistorial variables, and the algebraic structures of these. Some
unsolved problems are identified.Comment: 5 pages, Goteborg-ITP-94-24, plain te
Conformal Symmetry and Duality between Free Particle, H-atom and Harmonic Oscillator
We establish a duality between the free massless relativistic particle in d
dimensions, the non-relativistic hydrogen atom (1/r potential) in (d-1) space
dimensions, and the harmonic oscillator in (d-2) space dimensions with its mass
given as the lightcone momentum of an additional dimension. The duality is in
the sense that the classical action of these systems are gauge fixed forms of
the same worldline gauge theory action at the classical level, and they are all
described by the same unitary representation of the conformal group SO(d,2) at
the quantum level. The worldline action has a gauge symmetry Sp(2) which treats
canonical variables (x,p) as doublets and exists only with a target spacetime
that has d spacelike dimensions and two timelike dimensions. This spacetime is
constrained due to the gauge symmetry, and the various dual solutions
correspond to solutions of the constraints with different topologies. For
example, for the H-atom the two timelike dimensions X^{0'},X^{0} live on a
circle. The model provides an example of how realistic physics can be viewed as
existing in a larger covariant space that includes two timelike coordinates,
and how the covariance in the larger space unifies different looking physics
into a single system.Comment: Latex, 23 pages, minor improvements. In v3 a better gauge choice for
u for the H-atom is made; the results are the sam
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