1,355 research outputs found
Daylight operation of a free space, entanglement-based quantum key distribution system
Many quantum key distribution (QKD) implementations using a free space
transmission path are restricted to operation at night time in order to
distinguish the signal photons used for a secure key establishment from
background light. Here, we present a lean entanglement-based QKD system
overcoming that imitation. By implementing spectral, spatial and temporal
filtering techniques, we were able to establish a secure key continuously over
several days under varying light and weather conditions.Comment: 13 pages, 6 figure
Experimental quantum key distribution based on a Bell test
We report on a complete free-space field implementation of a modified Ekert91
protocol for quantum key distribution using entangled photon pairs. For each
photon pair we perform a random choice between key generation and a Bell
inequality. The amount of violation is used to determine the possible knowledge
of an eavesdropper to ensure security of the distributed final key.Comment: 5 pages ReVTeX, 3 figures; version v2 with updated references and
minor corrections, author spelling fixe
Low-scale inflation in a model of dark energy and dark matter
We present a complete particle physics model that explains three major
problems of modern cosmology: inflation, dark matter and dark energy, and also
gives a mechanism for leptogenesis. The model has a new gauge group
that grows strong at a scale eV. We focus on the
inflationary aspects of the model. Inflation occurs with a Coleman-Weinberg
potential at a low scale, down to \sim 6\times 10^5\gev, being compatible
with observational data.Comment: 5 two-column pages, RevTex4; two reference added and minor changes
made in the text; published in JCA
To a New Normal: Surgery and COVID-19 During the Transition Phase
Surgeons and surgery departments have shown resilience in responding to the COVID-19 pandemic. As the situation stabilizes, it will be necessary to adopt new strategies to move into the transition phase and eventually the full recovery phase
Where are the Walls?
The reported spatial variation in the fine-structure constant at high
redshift, if physical, could be due to the presence of dilatonic domains, and
one or more domain walls inside our horizon. An absorption spectrum of an
object in a different domain from our own would be characterized by a different
value of alpha. We show that while a single wall solution is statically
comparable to a dipole fit, and is a big improvement over a weighted mean
(despite adding 3 parameters), a two-wall solution is a far better fit (despite
adding 3 parameters over the single wall solution). We derive a simple model
accounting for the two-domain wall solution. The goodness of these fits is
however dependent on the extra random error which was argued to account for the
large scatter in most of the data. When this error is omitted, all the above
solutions are poor fits to the data. When included, the solutions that exhibit
a spatial dependence agree with the data much more significantly than the
Standard Model; however, the Standard Model itself is not a terrible fit to the
data, having a p-value of ~ 20 %
Parecença entre acessos de feijoeiro comum de grãos brancos utilizando o método de Harrison.
O objetivo deste trabalho foi estudar o coeficiente de parecença através da aplicação do modelo de Harrison, em variáveis qualitativas multicategóricas e determinar a matriz de distâncias entre acessos tradicionais de feijoeiro comum visando detectar possíveis redundâncias entre acessos.bitstream/CNPAF-2010/29749/1/comt-181.pd
Reconstructing a model of quintessential inflation
We present an explicit cosmological model where inflation and dark energy
both could arise from the dynamics of the same scalar field. We present our
discussion in the framework where the inflaton field attains a nearly
constant velocity (where
is the e-folding time) during inflation. We show that the model
with and can easily satisfy inflationary constraints,
including the spectral index of scalar fluctuations (),
tensor-to-scalar ratio () and also the bound imposed on
during the nucleosynthesis epoch (). In our
construction, the scalar field potential always scales proportionally to the
square of the Hubble expansion rate. One may thereby account for the two vastly
different energy scales associated with the Hubble parameters at early and late
epochs. The inflaton energy could also produce an observationally significant
effective dark energy at a late epoch without violating local gravity tests.Comment: 18 pages, 7 figures; added refs, published versio
New bulk scalar field solutions in brane worlds
We use nonlinear perturbation theory to obtain new solutions for brane world
models that incorporate a massive bulk scalar field. We then consider tensor
perturbations and show that Newtonian gravity is recovered on the brane for
both a light scalar field and for a bulk field with large negative mass. This
latter result points to the viability of higher-derivative theories of gravity
in the context of bulk extra dimensions.Comment: 4+\epsilon pages, no figure
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