13,617 research outputs found
Light Collimation and Focussing by a Thin Flat Metallic Slab
We present experimental and theoretical work showing that a flat metallic
slab can collimate and focus light impinging on the slab from a punctual
source. The effect is optimised when the radiation is around the bulk, not at
the surface, plasma frequency. And the smaller the imaginary part of the
permittivity is, the better the collimation. Experiments for Ag in the visible
as well as calculations are presented. We also discuss the interesting case of
the Aluminium whose imaginary part of the permittivity is very small at the
plasma frequency in UV radiation. Generalization to other materials and
radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette
No-Scale Inflation
Supersymmetry is the most natural framework for physics above the TeV scale,
and the corresponding framework for early-Universe cosmology, including
inflation, is supergravity. No-scale supergravity emerges from generic string
compactifications and yields a non-negative potential, and is therefore a
plausible framework for constructing models of inflation. No-scale inflation
yields naturally predictions similar to those of the Starobinsky model based on
gravity, with a tilted spectrum of scalar perturbations: , and small values of the tensor-to-scalar perturbation ratio ,
as favoured by Planck and other data on the cosmic microwave background (CMB).
Detailed measurements of the CMB may provide insights into the embedding of
inflation within string theory as well as its links to collider physics.Comment: Invited contribution to the forthcoming Classical and Quantum Gravity
focus issue on "Planck and the fundamentals of cosmology". 22 pages, 7
figures, uses psfra
Phenomenological Aspects of No-Scale Inflation Models
We discuss phenomenological aspects of no-scale supergravity inflationary
models motivated by compactified string models, in which the inflaton may be
identified either as a K\"ahler modulus or an untwisted matter field, focusing
on models that make predictions for the scalar spectral index and the
tensor-to-scalar ratio that are similar to the Starobinsky model. We
discuss possible patterns of soft supersymmetry breaking, exhibiting examples
of the pure no-scale type , of the CMSSM type with
universal and at a high scale, and of the mSUGRA type with
boundary conditions at the high input scale. These may be
combined with a non-trivial gauge kinetic function that generates gaugino
masses , or one may have a pure gravity mediation scenario where
trilinear terms and gaugino masses are generated through anomalies. We also
discuss inflaton decays and reheating, showing possible decay channels for the
inflaton when it is either an untwisted matter field or a K\"ahler modulus.
Reheating is very efficient if a matter field inflaton is directly coupled to
MSSM fields, and both candidates lead to sufficient reheating in the presence
of a non-trivial gauge kinetic function.Comment: 41 pages, 6 figure
A No-Scale Inflationary Model to Fit Them All
The magnitude of B-mode polarization in the cosmic microwave background as
measured by BICEP2 favours models of chaotic inflation with a quadratic potential, whereas data from the Planck satellite favour a small
value of the tensor-to-scalar perturbation ratio that is highly consistent
with the Starobinsky model. Reality may lie somewhere between these
two scenarios. In this paper we propose a minimal two-field no-scale
supergravity model that interpolates between quadratic and Starobinsky-like
inflation as limiting cases, while retaining the successful prediction .Comment: 25 pages, 12 figure
Calculations of Inflaton Decays and Reheating: with Applications to No-Scale Inflation Models
We discuss inflaton decays and reheating in no-scale Starobinsky-like models
of inflation, calculating the effective equation-of-state parameter, ,
during the epoch of inflaton decay, the reheating temperature, ,
and the number of inflationary e-folds, , comparing analytical
approximations with numerical calculations. We then illustrate these results
with applications to models based on no-scale supergravity and motivated by
generic string compactifications, including scenarios where the inflaton is
identified as an untwisted-sector matter field with direct Yukawa couplings to
MSSM fields, and where the inflaton decays via gravitational-strength
interactions. Finally, we use our results to discuss the constraints on these
models imposed by present measurements of the scalar spectral index and
the tensor-to-scalar perturbation ratio , converting them into constraints
on , the inflaton decay rate and other parameters of specific no-scale
inflationary models.Comment: 33 pages, 14 figure
Influence of substrate types and reflector proximities over a NDTC antenna
The influence of dissimilar substrates and reflector proximities over a newly developed Non-uniformly Distributed-Turns Coil (NDTC) antenna for High-Frequency (HF) Radio Frequency IDentification (RFID) applications is presented. In the study, the performance of the HF-RFID NDTC antenna over various substrates with deposited conductor thicknesses is conducted. In addition, the effect over a conceivably encountered reflector in the proximity of the antenna is considered. Insensitive reflection coefficient (S11) responses for different substrate permittivities were experienced and the diverse conductor types and thicknesses contributed to a compromised magnetic-field (H-field) and recalculated matching network. The matching network additionally preserves resonance when the antennas is in close proximity to the reflector and a predictable H-field response for the separation range is shown
Starobinsky-like Inflation, Supercosmology and Neutrino Masses in No-Scale Flipped SU(5)
We embed a flipped GUT model in a no-scale
supergravity framework, and discuss its predictions for cosmic microwave
background observables, which are similar to those of the Starobinsky model of
inflation. Measurements of the tilt in the spectrum of scalar perturbations in
the cosmic microwave background, , constrain significantly the model
parameters. We also discuss the model's predictions for neutrino masses, and
pay particular attention to the behaviours of scalar fields during and after
inflation, reheating and the GUT phase transition. We argue in favor of strong
reheating in order to avoid excessive entropy production which could dilute the
generated baryon asymmetry.Comment: 51 pages, 13 figure
Post-Inflationary Gravitino Production Revisited
We revisit gravitino production following inflation. As a first step, we
review the standard calculation of gravitino production in the thermal plasma
formed at the end of post-inflationary reheating when the inflaton has
completely decayed. Next we consider gravitino production prior to the
completion of reheating, assuming that the inflaton decay products thermalize
instantaneously while they are still dilute. We then argue that instantaneous
thermalization is in general a good approximation, and also show that the
contribution of non-thermal gravitino production via the collisions of inflaton
decay products prior to thermalization is relatively small. Our final estimate
of the gravitino-to-entropy ratio is approximated well by a standard
calculation of gravitino production in the post-inflationary thermal plasma
assuming total instantaneous decay and thermalization at a time . Finally, in light of our calculations, we consider potential
implications of upper limits on the gravitino abundance for models of
inflation, with particular attention to scenarios for inflaton decays in
supersymmetric Starobinsky-like models.Comment: 34 pages, 7 figures, uses psfra
Starobinsky-Like Inflation and Neutrino Masses in a No-Scale SO(10) Model
Using a no-scale supergravity framework, we construct an SO(10) model that
makes predictions for cosmic microwave background observables similar to those
of the Starobinsky model of inflation, and incorporates a double-seesaw model
for neutrino masses consistent with oscillation experiments and late-time
cosmology. We pay particular attention to the behaviour of the scalar fields
during inflation and the subsequent reheating.Comment: 38 pages, 8 figure
High-Level Correlated Approach to the Jellium Surface Energy, Without Uniform-Electron-Gas Input
We resolve the long-standing controversy over the surface energy of simple
metals: Density functional methods that require uniform-electron-gas input
agree with each other at many levels of sophistication, but not with high-level
correlated calculations like Fermi Hypernetted Chain and Diffusion Monte Carlo
(DMC) that predict the uniform-gas correlation energy. Here we apply a very
high-level correlated approach, the inhomogeneous Singwi-Tosi-Land-Sj\"olander
(ISTLS) method, and find that the density functionals are indeed reliable
(because the surface energy is "bulk-like"). ISTLS values are close to
recently-revised DMC values. Our work also vindicates the previously-disputed
use of uniform-gas-based nonlocal kernels in time-dependent density functional
theory.Comment: 4 pages, 1 figur
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