123,350 research outputs found
Supersymmetric SO(10) Grand Unification at the LHC and Beyond
We study models of supersymmetric grand unification based on the SO(10) gauge
group. We investigate scenarios of non-universal gaugino masses including
models containing a mixture of two representations of hidden sector chiral
superfields. We analyse the effect of excluding mu from the fine-tuning
measure, and confront the results with low energy constraints, including the
Higgs boson mass, dark matter relic density and supersymmetry bounds. We also
determine high scale Yukawa coupling ratios and confront the results with
theoretical predictions. Finally, we present two additional benchmarks that
should be explored at the LHC and future colliders.Comment: Published versio
A New S-S' Pair Creation Rate Expression Improving Upon Zener Curves for I-E Plots
To simplify phenomenology modeling used for charge density wave
(CDW)transport, we apply a wavefunctional formulation of tunneling Hamiltonians
to a physical transport problem characterized by a perturbed washboard
potential. To do so, we consider tunneing between states that are
wavefunctionals of a scalar quantum field. I-E curves that match Zener curves -
used to fit data experimentally with wavefunctionals congruent with the false
vacuum hypothesis. This has a very strong convergence with electron-positron
pair production representations.The similarities in plot behavior of the
current values after the threshold electric field values argue in favor of the
Bardeen pinning gap paradigm proposed for quasi-one-dimensional metallic
transport problems.Comment: 22 pages,6 figures, and extensive editing of certain segments.Paper
has been revised due to acceptance by World press scientific MPLB journal.
This is word version of file which has been submitted to MPLBs editor for
final proofing. Due for publication perhaps in mid spring to early summer
200
A fully (3+1)-D Regge calculus model of the Kasner cosmology
We describe the first discrete-time 4-dimensional numerical application of
Regge calculus. The spacetime is represented as a complex of 4-dimensional
simplices, and the geometry interior to each 4-simplex is flat Minkowski
spacetime. This simplicial spacetime is constructed so as to be foliated with a
one parameter family of spacelike hypersurfaces built of tetrahedra. We
implement a novel two-surface initial-data prescription for Regge calculus, and
provide the first fully 4-dimensional application of an implicit decoupled
evolution scheme (the ``Sorkin evolution scheme''). We benchmark this code on
the Kasner cosmology --- a cosmology which embodies generic features of the
collapse of many cosmological models. We (1) reproduce the continuum solution
with a fractional error in the 3-volume of 10^{-5} after 10000 evolution steps,
(2) demonstrate stable evolution, (3) preserve the standard deviation of
spatial homogeneity to less than 10^{-10} and (4) explicitly display the
existence of diffeomorphism freedom in Regge calculus. We also present the
second-order convergence properties of the solution to the continuum.Comment: 22 pages, 5 eps figures, LaTeX. Updated and expanded versio
Effective Operators for Double-Beta Decay
We use a solvable model to examine double-beta decay, focusing on the
neutrinoless mode. After examining the ways in which the neutrino propagator
affects the corresponding matrix element, we address the problem of finite
model-space size in shell-model calculations by projecting our exact wave
functions onto a smaller subspace. We then test both traditional and more
recent prescriptions for constructing effective operators in small model
spaces, concluding that the usual treatment of double-beta-decay operators in
realistic calculations is unable to fully account for the neglected parts of
the model space. We also test the quality of the Quasiparticle Random Phase
Approximation and examine a recent proposal within that framework to use
two-neutrino decay to fix parameters in the Hamiltonian. The procedure
eliminates the dependence of neutrinoless decay on some unfixed parameters and
reduces the dependence on model-space size, though it doesn't eliminate the
latter completely.Comment: 10 pages, 8 figure
An open question: Are topological arguments helpful in setting initial conditions for transport problems in condensed matter physics?
The tunneling Hamiltonian is a proven method to treat particle tunneling
between different states represented as wavefunctions in many-body physics. Our
problem is how to apply a wave functional formulation of tunneling Hamiltonians
to a driven sine-Gordon system. We apply a generalization of the tunneling
Hamiltonian to charge density wave (CDW) transport problems in which we
consider tunneling between states that are wavefunctionals of a scalar quantum
field. We present derived I-E curves that match Zenier curves used to fit data
experimentally with wavefunctionals congruent with the false vacuum hypothesis.
THe open question is whether the coefficients picked in both the
wavefunctionals and the magnitude of the coefficents of the driven sine Gordon
physical system should be picked by topological charge arguements that in
principle appear to assign values that have a tie in with the false vacuum
hypothesis first presented by Sidney ColemanComment: 17 pages, 4 figures (1a to 2b) on two pages. Specific emphasis on if
or not topological arguements a la Trodden, Su et al add to formulation of
condensed matter transport problem
A comparison of the optical properties of radio-loud and radio-quiet quasars
We have made radio observations of 87 optically selected quasars at 5 GHz
with the VLA in order to measure the radio power for these objects and hence
determine how the fraction of radio-loud quasars varies with redshift and
optical luminosity. The sample has been selected from the recently completed
Edinburgh Quasar Survey and covers a redshift range of 0.3 < z < 1.5 and an
optical absolute magnitude range of -26.5 < M_{B} < -23.5 (h, q_{0} = 1/2). We
have also matched up other existing surveys with the FIRST and NVSS radio
catalogues and combined these data so that the optical luminosity-redshift
plane is now far better sampled than previously. We have fitted a model to the
probability of a quasar being radio-loud as a function of absolute magnitude
and redshift and from this model infer the radio-loud and radio-quiet optical
luminosity functions. The radio-loud optical luminosity function is featureless
and flatter than the radio-quiet one. It evolves at a marginally slower rate if
quasars evolve by density evolution, but the difference in the rate of
evolutions of the two different classes is much less than was previously
thought. We show, using Monte-Carlo simulations, that the observed difference
in the shape of the optical luminosity functions can be partly accounted for by
Doppler boosting of the optical continuum of the radio-loud quasars and explain
how this can be tested in the future.Comment: 33 pages, 9 postscript figures, uses the AAS aaspp4 LaTeX style file,
to appear in the 1 February 1999 issue of The Astrophysical Journa
An optical NMR spectrometer for Larmor-beat detection and high-resolution POWER NMR
Optical nuclear magnetic resonance (ONMR) is a powerful probe of electronic properties in III-V semiconductors. Larmor-beat detection (LBD) is a sensitivity optimized, time-domain NMR version of optical detection based on the Hanle effect. Combining LBD ONMR with the line-narrowing method of POWER (perturbations observed with enhanced resolution) NMR further enables atomically detailed views of local electronic features in III-Vs. POWER NMR spectra display the distribution of resonance shifts or line splittings introduced by a perturbation, such as optical excitation or application of an electric field, that is synchronized with a NMR multiple-pulse time-suspension sequence. Meanwhile, ONMR provides the requisite sensitivity and spatial selectivity to isolate local signals within macroscopic samples. Optical NMR, LBD, and the POWER method each introduce unique demands on instrumentation. Here, we detail the design and implementation of our system, including cryogenic, optical, and radio-frequency components. The result is a flexible, low-cost system with important applications in semiconductor electronics and spin physics. We also demonstrate the performance of our systems with high-resolution ONMR spectra of an epitaxial AlGaAs/GaAs heterojunction. NMR linewidths down to 4.1 Hz full width at half maximum were obtained, a 10^3-fold resolution enhancement relative any previous optically detected NMR experiment
Structural relaxation in Morse clusters: Energy landscapes
We perform a comprehensive survey of the potential energy landscapes of
13-atom Morse clusters, and describe how they can be characterized and
visualized. Our aim is to detail how the global features of the funnel-like
surface change with the range of the potential, and to relate these changes to
the dynamics of structural relaxation. We find that the landscape becomes
rougher and less steep as the range of the potential decreases, and that
relaxation paths to the global minimum become more complicated.Comment: 21 pages, 3 tables, 5 figure
A helium-3 refrigerator employing capillary confinement of liquid cryogen
A condensation refrigerator suitable for operation in a zero gravity space environment was constructed. The condensed liquid refrigerant is confined by surface tension inside a porous metal matrix. Helium-4 and helium-3 gases were condensed and held in a copper matrix. Evaporative cooling of confined liquid helium-4 resulted in a temperature of 1.4K. Using a zeolite adsorption pump external to the cryostat, a temperature of 0.6 K was achieved through evaporative cooling of liquid helium-3. The amount of time required for complete evaporation of a controlled mass of liquid helium-4 contained in the copper matrix was measured as a function of the applied background power. For heating powers below 18 mW the measured times are consistent with the normal boiling of the confined volume of liquid refrigerant. At background powers above 18 mW the rapid rise in the temperature of the copper matrix the signature of the absence of confined liquid occurs in a time a factor of two shorter than that expected on the basis of an extrapolation of the low power data
Opening angles, Lorentz factors and confinement of X-ray binary jets
We present a collation of the available data on the opening angles of jets in
X-ray binaries, which in most cases are small (less than 10 degrees). Under the
assumption of no confinement, we calculate the Lorentz factors required to
produce such small opening angles via the transverse relativistic Doppler
effect. The derived Lorentz factors, which are in most cases lower limits, are
found to be large, with a mean greater than 10, comparable to those estimated
for AGN and much higher than the commonly-assumed values for X-ray binaries of
2 to 5. Jet power constraints do not in most cases rule out such high Lorentz
factors. The upper limits on the opening angles show no evidence for smaller
Lorentz factors in the steady jets of Cygnus X-1 and GRS 1915+105. In those
sources in which deceleration has been observed (notably XTE J1550-564 and
Cygnus X-3), some confinement of the jets must be occurring, and we briefly
discuss possible confinement mechanisms. It is however possible that all the
jets could be confined, in which case the requirement for high bulk Lorentz
factors can be relaxed.Comment: 11 pages, 4 figures (2 colour), accepted for publication in MNRA
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