2,783 research outputs found
Project Tektite 1 - A multiagency 60 day saturated dive conducted by the United States Navy, the National Aeronautics and Space Administration, the Department of the Interior, and the General Electric Company Summary report
Underwater research in ocean floor habitat for 60 day evaluation of supporting facilities at Virgin Islands for Tektite 1 projec
Masses of the physical mesons from an effective QCD--Hamiltonian
The front form Hamiltonian for quantum chromodynamics, reduced to an
effective Hamiltonian acting only in the space, is solved
approximately. After coordinate transformation to usual momentum space and
Fourier transformation to configuration space a second order differential
equation is derived. This retarded Schr\"odinger equation is solved by
variational methods and semi-analytical expressions for the masses of all 30
pseudoscalar and vector mesons are derived. In view of the direct relation to
quantum chromdynamics without free parameter, the agreement with experiment is
remarkable, but the approximation scheme is not adequate for the mesons with
one up or down quark. The crucial point is the use of a running coupling
constant , in a manner similar but not equal to the one of
Richardson in the equal usual-time quantization. Its value is fixed at the Z
mass and the 5 flavor quark masses are determined by a fit to the vector meson
quarkonia.Comment: 18 pages, 4 Postscript figure
Non-Perturbative Spectrum of Two Dimensional (1,1) Super Yang-Mills at Finite and Large N
We consider the dimensional reduction of N = 1 SYM_{2+1} to 1+1 dimensions,
which has (1,1) supersymmetry. The gauge groups we consider are U(N) and SU(N),
where N is a finite variable. We implement Discrete Light-Cone Quantization to
determine non-perturbatively the bound states in this theory. A careful
analysis of the spectrum is performed at various values of N, including the
case where N is large (but finite), allowing a precise measurement of the 1/N
effects in the quantum theory. The low energy sector of the theory is shown to
be dominated by string-like states. The techniques developed here may be
applied to any two dimensional field theory with or without supersymmetry.Comment: LaTex 18 pages; 5 Encapsulated PostScript figure
String Spectrum of 1+1-Dimensional Large N QCD with Adjoint Matter
We propose gauging matrix models of string theory to eliminate unwanted
non-singlet states. To this end we perform a discretised light-cone
quantisation of large N gauge theory in 1+1 dimensions, with scalar or
fermionic matter fields transforming in the adjoint representation of SU(N).
The entire spectrum consists of bosonic and fermionic closed-string
excitations, which are free as N tends to infinity. We analyze the general
features of such bound states as a function of the cut-off and the gauge
coupling, obtaining good convergence for the case of adjoint fermions. We
discuss possible extensions of the model and the search for new non-critical
string theories.Comment: 20 pages (7 figures available from authors as postscipt files),
PUPT-134
Operator normalized quantum arrival times in the presence of interactions
We model ideal arrival-time measurements for free quantum particles and for
particles subject to an external interaction by means of a narrow and weak
absorbing potential. This approach is related to the operational approach of
measuring the first photon emitted from a two-level atom illuminated by a
laser. By operator-normalizing the resulting time-of-arrival distribution, a
distribution is obtained which for freely moving particles not only recovers
the axiomatically derived distribution of Kijowski for states with purely
positive momenta but is also applicable to general momentum components. For
particles interacting with a square barrier the mean arrival time and
corresponding ``tunneling time'' obtained at the transmission side of the
barrier becomes independent of the barrier width (Hartman effect) for
arbitrarily wide barriers, i.e., without the transition to the ultra-opaque,
classical-like regime dominated by wave packet components above the barrier.Comment: 10 pages, 5 figures, RevTe
-Dimensional Large QCD coupled to Adjoint Fermions
We consider 1+1-dimensional QCD coupled to Majorana fermions in the adjoint
representation of the gauge group . Pair creation of partons (fermion
quanta) is not suppressed in the large- limit, where the glueball-like bound
states become free. In this limit the spectrum is given by a linear \lc\ Schr\"
odinger equation, which we study numerically using the discretized \lcq. We
find a discrete spectrum of bound states, with the logarithm of the level
density growing approximately linearly with the mass. The wave function of a
typical excited state is a complicated mixture of components with different
parton numbers. A few low-lying states, however, are surprisingly close to
being eigenstates of the parton number, and their masses can be accurately
calculated by truncated diagonalizations.Comment: 22 pages + 9 figures (available by request from
[email protected]), uses phyzzx.tex + tables.tex PUPT-1413,
IASSNS-HEP-93/4
Model for SU(3) vacuum degeneracy using light-cone coordinates
Working in light-cone coordinates, we study the zero-modes and the vacuum in
a 2+1 dimensional SU(3) gauge model. Considering the fields as independent of
the tranverse variables, we dimensionally reduce this model to 1+1 dimensions.
After introducing an appropriate su(3) basis and gauge conditions, we extract
an adjoint field from the model. Quantization of this adjoint field and field
equations lead to two constrained and two dynamical zero-modes. We link the
dynamical zero-modes to the vacuum by writing down a Schrodinger equation and
prove the non-degeneracy of the SU(3) vacuum provided that we neglect the
contribution of constrained zero-modes.Comment: 22 pages, 5 figure
A synthetic population of Wolf-Rayet stars in the LMC based on detailed single and binary star evolution models
Without doubt, mass transfer in close binary systems contributes to the
populations of Wolf-Rayet (WR) stars in the Milky Way and the Magellanic
Clouds. However, the binary formation channel is so far not well explored. We
want to remedy this by exploring large grids of detailed binary and single star
evolution models computed with the publicly available MESA code, for a
metallicity appropriate for the Large Magellanic Cloud (LMC). The binary models
are calculated through Roche-lobe overflow and mass transfer, until the
initially more massive star exhausts helium in its core. We distinguish models
of WR and helium stars based on the estimated stellar wind optical depth. We
use these models to build a synthetic WR population, assuming constant star
formation. Our models can reproduce the WR population of the LMC to significant
detail, including the number and luminosity functions of the main WR subtypes.
We find that for binary fractions of 100% (50%), all LMC WR stars below
() are stripped binary mass donors. We
also identify several insightful mismatches. With a single star fraction of
50\%, our models produce too many yellow supergiants, calling either for a
larger initial binary fraction, or for enhanced mass-loss near the
Humphreys-Davidson limit. Our models predict more long-period WR binaries than
observed, arguably due to an observational bias towards short periods. Our
models also underpredict the shortest-period WR binaries, which may have
implications for understanding the progenitors of double black hole mergers.
The fraction of binary produced WR stars may be larger than often assumed, and
outline the risk to mis-calibrate stellar physics when only single star models
are used to reproduce the observed WR stars.Comment: 15 pages + 13 pages appendix, 14 figures, 2 table
Evolution of the interfacial structure of LaAlO3 on SrTiO3
The evolution of the atomic structure of LaAlO3 grown on SrTiO3 was
investigated using surface x-ray diffraction in conjunction with
model-independent, phase-retrieval algorithms between two and five monolayers
film thickness. A depolarizing buckling is observed between cation and oxygen
positions in response to the electric field of polar LaAlO3, which decreases
with increasing film thickness. We explain this in terms of competition between
elastic strain energy, electrostatic energy, and electronic reconstructions.
The findings are qualitatively reproduced by density-functional theory
calculations. Significant cationic intermixing across the interface extends
approximately three monolayers for all film thicknesses. The interfaces of
films thinner than four monolayers therefore extend to the surface, which might
affect conductivity
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