102,837 research outputs found
Cosmological Evolution on Self-Tuned Branes and the Cosmological Constant
We consider the cosmological evolution of a bulk scalar field and ordinary
matter living on the brane world in the light of the constraints imposed by the
matter dominated cosmological evolution and a small cosmological constant now.
We rule out models with a self-tuned minimum of the four dimensional potential
as they would lead to rapid oscillations of the Hubble parameter now. A more
natural framework is provided by supergravity in singular spaces where the
brane coupling and the bulk potential are related by supersymmetry leading to a
four dimensional run-away potential. For late times we obtain an accelerating
universe due to the breaking of supersymmetry on the brane with an acceleration
parameter of q_0=-4/7 and associated equation of state omega=-5/7.Comment: 24 pages, JHEP styl
Conformal Inflation Coupled to Matter
We formulate new conformal models of inflation and dark energy which
generalise the Higgs-Dilaton scenario. We embed these models in unimodular
gravity whose effect is to break scale invariance in the late time Universe. In
the early Universe, inflation occurs close to a maximum of both the scalar
potential and the scalar coupling to the Ricci scalar in the Jordan frame. At
late times, the dilaton, which decouples from the dynamics during inflation,
receives a potential term from unimodular gravity and leads to the acceleration
of the Universe. We address two central issues in this scenario. First we show
that the Damour-Polyalov mechanism, when non-relativistic matter is present
prior to the start of inflation, sets the initial conditions for inflation at
the maximum of the scalar potential. We then show that conformal invariance
implies that matter particles are not coupled to the dilaton in the late
Universe at the classical level. When fermions acquire masses at low energy,
scale invariance is broken and quantum corrections induce a coupling between
the dilaton and matter which is still small enough to evade the gravitational
constraints in the solar system.Comment: 24 page
Fatigue failure load indicator
An indicator for recording the load at which a fatigue specimen breaks during the last cycle of a fatigue test is described. A load cell is attached to the specimen which is alternately subjected to tension and compression loads. The output of the load cell which is proportional to the load on the specimen is applied to the input of a peak detector. Each time the specimen is subjected to a compression load, means are provided for applying a positive voltage to the rest of the peak detector to reset it. During the last cycle of the tension load the peak detector measures the maximum load on the specimen. Means are provided for disconnecting the load cell from the peak detector when there is a failure in the specimen
Cosmic Strings, Zero Modes and SUSY breaking in Nonabelian N=1 Gauge Theories
We investigate the microphysics of cosmic strings in Nonabelian gauge
theories with N=1 supersymmetry. We give the vortex solutions in a specific
example and demonstrate that fermionic superconductivity arises because of the
couplings and interactions dictated by supersymmetry. We then use supersymmetry
transformations to obtain the relevant fermionic zero modes and investigate the
role of soft supersymmetry breaking on the existence and properties of the
superconducting strings.Comment: 12 pages, RevTex, submitted to Phys. Rev.
Configurations of Handles and the Classification of Divergences in the String Partition Function
The divergences that arise in the regularized partition function for closed
bosonic string theory in flat space lead to three types of perturbation series
expansions, distinguished by their genus dependence. This classification of
infinities can be traced to geometrical characteristics of the string
worldsheet. Some categories of divergences may be eliminated in string theories
formulated on compact manifolds.Comment: 24 pages, DAMTP-R/94/1
Light controlled photon tunneling
Recent measurements of photon tunneling through individual subwavelength
pinholes in a gold film covered with a layer of polydiacetylene (Phys. Rev.
Letters 88, 187402 (2002)) provided strong indication of "photon blockade"
effect similar to Coulomb blockade phenomenon observed in single-electron
tunneling experiments. Here we report first observation of photon tunneling
been blocked (gated) by light at a different wavelength. This observation
suggests possibility of building new class of photon tunneling gating devices
for all-optical signal processing.Comment: 11 pages, 3 figure
Brane-World Cosmology, Bulk Scalars and Perturbations
We investigate aspects of cosmology in brane world theories with a bulk
scalar field. We concentrate on a recent model motivated from supergravity in
singular spaces. After discussing the background evolution of such a
brane-world, we present the evolution of the density contrast. We compare our
results to those obtained in the (second) Randall-Sundrum scenario and usual 4D
scalar-tensor theories.Comment: 29 pages, one figure, JHEP3-styl
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