111 research outputs found
Controlling the path of discretized light in waveguide lattices
A general method for flexible control of the path of discretized light beams
in homogeneous waveguide lattices, based on longitudinal modulation of the
coupling constant, is theoretically proposed. As compared to beam steering and
refraction achievable in graded-index waveguide arrays, the proposed approach
enables to synthesize rather arbitrary target paths
Transformaciones de haz mediante microlentes selfoc activas
[EN]: In this paper light propagation in an active selfoc microlens with complex refractive index and gradient parameter are examined. The ray-transfer matrix of an active material regarded as a diffraction-free first order optical system is presented to describe the beam transformations in active selfoc microlenses. Results concerning Gaussian beam transformationsand on-axis irradiance through the active selfoc microlens are discussed and commented. © Sociedad Española de Óptica.[ES]: En este trabajo se estudia la propagación de la luz a través de una microlente selfoc activa con un índice de refracción y parámetro de gradiente complejos. La matriz de transferencia de rayos, vista como un sistema óptico de primer orden libre de efectos de difracción, es introducida para describir las transformaciones que puede sufrir un haz en microlentes selfoc activas. Por último se presentan y comentan los resultados correspondientes a las transformaciones de haces Gaussianos y a la irradiancia en eje a través de la microlente selfoc activa.This work has been sponsored by Xunta de Galicia/Feder (INCITE08PXIB206013PR), Ministerio de Ciencia e Innovación (MAT2010-18519) and CDTI (SURFALUX SOL-00030930), Spain. Besides, Ana I. Gomez-Varela wants to acknowledge the financial support from the FPU (Formación de Profesorado Universitario) grant 2009 (Ministerio de Educación, Spain).Peer Reviewe
The lightest scalar in theories with broken supersymmetry
We study the scalar mass matrix of general supersymmetric theories with local
gauge symmetries, and derive an absolute upper bound on the lightest scalar
mass. This bound can be saturated by suitably tuning the superpotential, and
its positivity therefore represents a necessary and sufficient condition for
the existence of metastable vacua. It is derived by looking at the subspace of
all those directions in field space for which an arbitrary supersymmetric mass
term is not allowed and scalar masses are controlled by supersymmetry-breaking
splitting effects. This subspace includes not only the direction of
supersymmetry breaking, but also the directions of gauge symmetry breaking and
the lightest scalar is in general a linear combination of fields spanning all
these directions. We present explicit results for the simplest case of theories
with a single local gauge symmetry. For renormalizable gauge theories, the
lightest scalar is a combination of the Goldstino partners and its square mass
is always positive. For more general non-linear sigma models, on the other
hand, the lightest scalar can involve also the Goldstone partner and its square
mass is not always positive.Comment: 30 pages, 3 figures; v2 introduction expanded, paragraph added in
section 5 and two references adde
Electronic structure and exotic exchange splitting in spin-density-wave states of BaFeAs
The magnetic properties in the parent compounds are often intimately related
to the microscopic mechanism of superconductivity. Here we report the first
direct measurements on the electronic structure of a parent compound of the
newly discovered iron-based superconductor, BaFeAs, which provides a
foundation for further studies. We show that the energy of the spin density
wave (SDW) in BaFeAs is lowered through exotic exchange splitting of
the band structure, rather than Fermi surface nesting of itinerant electrons.
This clearly demonstrates that a metallic SDW state could be solely induced by
interactions of local magnetic moments, resembling the nature of
antiferromagnetic order in cuprate parent compounds.Comment: 5 pages, 4 figure
Universal de Sitter solutions at tree-level
Type IIA string theory compactified on SU(3)-structure manifolds with
orientifolds allows for classical de Sitter solutions in four dimensions. In
this paper we investigate these solutions from a ten-dimensional point of view.
In particular, we demonstrate that there exists an attractive class of de
Sitter solutions, whose geometry, fluxes and source terms can be entirely
written in terms of the universal forms that are defined on all SU(3)-structure
manifolds. These are the forms J and Omega, defining the SU(3)-structure
itself, and the torsion classes. The existence of such universal de Sitter
solutions is governed by easy-to-verify conditions on the SU(3)-structure,
rendering the problem of finding dS solutions purely geometrical. We point out
that the known (unstable) solution coming from the compactification on SU(2)x
SU(2) is of this kind.Comment: 20 pages, 3 figures, v2: added reference
Inflating in a Better Racetrack
We present a new version of our racetrack inflation scenario which, unlike
our original proposal, is based on an explicit compactification of type IIB
string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The axion-dilaton and
all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler
moduli are stabilized by a nonperturbative superpotential, which has been
explicitly computed. For this model we identify situations for which a linear
combination of the axionic parts of the two Kahler moduli acts as an inflaton.
As in our previous scenario, inflation begins at a saddle point of the scalar
potential and proceeds as an eternal topological inflation. For a certain range
of inflationary parameters, we obtain the COBE-normalized spectrum of metric
perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We discuss
possible changes of parameters of our model and argue that anthropic
considerations favor those parameters that lead to a nearly flat spectrum of
inflationary perturbations, which in our case is characterized by the spectral
index n_s = 0.95.Comment: 20 pages, 7 figures. Brief discussion on the non-gaussianity of this
model, one more figure of the field trajectories added as well as other minor
changes to the tex
CMS DAQ Event Builder Based on Gigabit Ethernet
The CMS Data Acquisition system is designed to build and filter events originating from approximately 500 data sources from the detector at a maximum Level 1 trigger rate of 100 kHz and with an aggregate throughput of 100 GByte/s. For this purpose different architectures and switch technologies have been evaluated. Events will be built in two stages: the first stage, the FED Builder, will be based on Myrinet technology and will pre-assemble groups of about 8 data sources. The next stage, the Readout Builder, will perform the building of full events. The requirement of one Readout Builder is to build events at 12.5 kHz with average size of 16 kBytes from 64 sources. In this paper we present the prospects of a Readout Builder based on TCP/IP over Gigabit Ethernet. Various Readout Builder architectures that we are considering are discussed. The results of throughput measurements and scaling performance are outlined as well as the preliminary estimates of the final performance. All these studies have been carried out at our test-bed farms that are made up of a total of 130 dual Xeon PCs interconnected with Myrinet and Gigabit Ethernet networking and switching technologies
The 2 Tbps "Data to Surface" System of the CMS Data Acquisition
The Data Acquisition system of the CMS experiment, at the CERN LHC collider, is designed to build 1~MB events at a sustained rate of 100 kHz and to provide sufficient computing power to filter the events by a factor of 1000. The Data to Surface (D2S) system is the first layer of the Data Acquisition interfacing the underground subdetector readout electronics to the surface Event Builder. It collects the 100~GB/s input data from a large number of front-end cards (650) , implements a first stage event building by combining multiple sources into lar ger-size data fragments, and transports them to the surface for the full event building. The Data to Surface system can operate at the maximum rate of 2 Tbps. This paper describes the layout, reconfigurability and production validation of the D2S system which is to be installed by December 2005
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