37,632 research outputs found
M-theory Inspired No-scale Supergravity
We propose a supergravity model that contains elements recently shown to
arise in the strongly-coupled limit of the heterotic string
(M-theory), including a no-scale--like K\"ahler potential, the identification
of the string scale with the gauge coupling unification scale, and the onset of
supersymmetry breaking at an intermediate scale determined by the size of the
eleventh dimension of M-theory. We also study the phenomenological consequences
of such scenario, which include a rather constrained sparticle spectrum within
the reach of present-generation particle accelerators.Comment: 8 pages, LaTeX, 3 figures (included
Deformation of a flexible fiber in a viscous flow past an obstacle
We study the deformation and transport of elastic fibers in a viscous
Hele-Shaw flow with curved streamlines. The variations of the global velocity
and orientation of the fiber follow closely those of the local flow velocity.
The ratios of the curvatures of the fibers by the corresponding curvatures of
the streamlines reflect a balance between elastic and viscous forces: this
ratio is shown experimentally to be determined by a dimensionless {\it Sperm
number} combining the characteristic parameters of the flow (transverse
velocity gradient, viscosity, fiber diameter/cell gap ratio) and those of the
fiber (diameter, effective length, Young's modulus). For short fibers, the
effective length is that of the fiber; for long ones, it is equal to the
transverse characteristic length of the flow. For , the
ratio of the curvatures increases linearly with ; For ,
the fiber reaches the same curvature as the streamlines
Qubitless Quantum Logic
We discuss the implementation of quantum logic in a system of strongly
interacting particles. The implementation is qubitless since ``logical qubits''
don't correspond to any physical two-state subsystems. As an illustration, we
present the results of simulations of the quantum controlled-NOT gate and
Shor's algorithm for a chain of spin-1/2 particles with Heisenberg coupling.
Our proposal extends the current theory of quantum information processing to
include systems with permanent strong coupling between the two-state
subsystems.Comment: 2 figures. Corrected titl
Simplified Metrics Calculation for Soft Bit Detection in DVB-T2
The constellation rotation and cyclic quadrature component delay (RQD) technique has been adopted in the second generation terrestrial digital video broadcasting (DVB-T2) standard. It improves the system performance under severe propagation conditions, but introduces serious complexity problems in the hardware implementation of the detection process. In this paper, we present a simplified scheme that greatly reduces the complexity of the demapper by simplifying the soft bit metrics computation having a negligible overall system performance loss
A Layman's guide to SUSY GUTs
The determination of the most straightforward evidence for the existence of
the Superworld requires a guide for non-experts (especially experimental
physicists) for them to make their own judgement on the value of such
predictions. For this purpose we review the most basic results of Super-Grand
unification in a simple and clear way. We focus the attention on two specific
models and their predictions. These two models represent an example of a direct
comparison between a traditional unified-theory and a string-inspired approach
to the solution of the many open problems of the Standard Model. We emphasize
that viable models must satisfy {\em all} available experimental constraints
and be as simple as theoretically possible. The two well defined supergravity
models, and , can be described in terms of only a few
parameters (five and three respectively) instead of the more than twenty needed
in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard
Model. A case of special interest is the strict no-scale
supergravity where all predictions depend on only one parameter (plus the
top-quark mass). A general consequence of these analyses is that supersymmetric
particles can be at the verge of discovery, lurking around the corner at
present and near future facilities. This review should help anyone distinguish
between well motivated predictions and predictions based on arbitrary choices
of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93,
CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is
available by request from [email protected]
Quintessence and cosmic acceleration
A cosmological model with perfect fluid and self-interacting quintessence
field is considered in the framework of the spatially flat
Friedmann-Robertson-Walker (FRW) geometry. By assuming that all physical
quantities depend on the volume scale factor of the Universe, the general
solution of the gravitational field equations can be expressed in an exact
parametric form. The quintessence field is a free parameter. With an
appropriate choice of the scalar field a class of exact solutions is obtained,
with an exponential type scalar field potential fixed via the gravitational
field equations. The general physical behavior of the model is consistent with
the recent cosmological scenario favored by supernova Type Ia observations,
indicating an accelerated expansion of the Universe.Comment: 6 pages, 3 figures, to appear in Int. J. Mod. Phys.
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