6,662 research outputs found
Four-wave mixing in slow light photonic crystal waveguides with very high group index
This work was supported by the EPSRC - UK Silicon Photonics consortium.We report efficient four-wave mixing in dispersion engineered slow light silicon photonic crystal waveguides with a flat band group index of n(g) = 60. Using only 15 mW continuous wave coupled input power, we observe a conversion efficiency of -28 dB. This efficiency represents a 30 dB enhancement compared to a silicon nanowire of the same length. At higher powers, thermal redshifting due to linear absorption was found to detune the slow light regime preventing the expected improvement in efficiency. We then overcome this thermal limitation by using oxide-clad waveguides, which we demonstrate for group indices of n(g) = 30. Higher group indices may be achieved with oxide clad-waveguides, and we predict conversion efficiencies approaching -10 dB, which is equivalent to that already achieved in silicon nanowires but for a 50x shorter length.Publisher PDFPeer reviewe
Flexible metamaterials at visible wavelengths
We report on the fabrication and characterization of plasmonic structures on flexible substrates (Metaflex) and demonstrate the optical properties of a single layer of Metaflex. The layer exhibits a plasmonic resonance in the visible region around 620 nm. We show experimental and numerical results for both nano-antennas and fishnet geometries. We anticipate the use of Metaflex as a building block for flexible metamaterials in the visible range.Publisher PDFPeer reviewe
Next--to--Leading Order QCD corrections for the --mixing with an extended Higgs sector
We present a calculation of the B0-B0--mixing including Next--to--Leading
Order (NLO) QCD corrections within the Two Higgs Doublet Model (2HDM). The QCD
corrections at NLO are contained in the factor denoted by eta_2 which modifies
the result obtained at the lowest order of perturbation theory. In the Standard
Model case, we confirm the results for eta_2 obtained by Buras, Jamin and
Weisz. The factor eta_2 is gauge and renormalization prescription invariant and
it does not depend on the infrared behaviour of the theory, which constitutes
an important test of the calculations. The NLO--calculations within the 2HDM
enhance the LO--result up to 18%, which affects the correlation between M_H and
V_{td}.Comment: 22 pages (LaTeX), 22 Postscript figures, version to appear in Nucl.
Phys. B, corrected some typos and a sign in the program, which results in
changes in Eqs. (71), (74) and (75). Due to these changes Eqs. (23) and (34)
may be written in a more compact wa
Ultracompact and low-power optical switch based on silicon photonic crystals
Switching light is one of the most fundamental functions of an optical circuit. As such, optical switches are a major research topic in photonics, and many types of switches have been realized. Most optical switches operate by imposing a phase shift between two sections of the device to direct light from one port to another, or to switch it on and off, the major constraint being that typical refractive index changes are very small. Conventional solutions address this issue by making long devices, thus increasing the footprint, or by using resonant enhancement, thus reducing the bandwidth. We present a slow-light-enhanced optical switch that is 36 times shorter than a conventional device for the same refractive index change and has a switching length of 5.2 m.The work was funded through the EU FP6-FET
“Splash” project and we acknowledge the Nanostructuring
Platform of EU FP6-NoE “epixnet” for technical
support. T. P. White is supported by an 1851
Royal Commission Research Fellowship
Event generation with SHERPA 1.1
In this paper the current release of the Monte Carlo event generator Sherpa,
version 1.1, is presented. Sherpa is a general-purpose tool for the simulation
of particle collisions at high-energy colliders. It contains a very flexible
tree-level matrix-element generator for the calculation of hard scattering
processes within the Standard Model and various new physics models. The
emission of additional QCD partons off the initial and final states is
described through a parton-shower model. To consistently combine multi-parton
matrix elements with the QCD parton cascades the approach of Catani, Krauss,
Kuhn and Webber is employed. A simple model of multiple interactions is used to
account for underlying events in hadron--hadron collisions. The fragmentation
of partons into primary hadrons is described using a phenomenological
cluster-hadronisation model. A comprehensive library for simulating tau-lepton
and hadron decays is provided. Where available form-factor models and matrix
elements are used, allowing for the inclusion of spin correlations; effects of
virtual and real QED corrections are included using the approach of Yennie,
Frautschi and Suura.Comment: 47 pages, 21 figure
Lepton flavor violation in low-scale seesaw models: SUSY and non-SUSY contributions
Taking the supersymmetric inverse seesaw mechanism as the explanation for
neutrino oscillation data, we investigate charged lepton flavor violation in
radiative and 3-body lepton decays as well as in neutrinoless
conversion in muonic atoms. In contrast to former studies, we take into account
all possible contributions: supersymmetric as well as non-supersymmetric. We
take CMSSM-like boundary conditions for the soft supersymmetry breaking
parameters. We find several regions where cancellations between various
contributions exist, reducing the lepton flavor violating rates by an order of
magnitude compared to the case where only the dominant contribution is taken
into account. This is in particular important for the correct interpretation of
existing data as well as for estimating the reach of near future experiments
where the sensitivity will be improved by one to two orders of magnitude.
Moreover, we demonstrate that ratios like BR()/BR() can be used to determine whether the supersymmetric contributions
dominate over the and contributions or vice versa.Comment: 75 pages, 7 figures. v3: references and comments added. Matches
published versio
MadEvent: Automatic Event Generation with MadGraph
We present a new multi-channel integration method and its implementation in
the multi-purpose event generator MadEvent, which is based on MadGraph. Given a
process, MadGraph automatically identifies all the relevant subprocesses,
generates both the amplitudes and the mappings needed for an efficient
integration over the phase space, and passes them to MadEvent. As a result, a
process-specific, stand-alone code is produced that allows the user to
calculate cross sections and produce unweighted events in a standard output
format. Several examples are given for processes that are relevant for physics
studies at present and forthcoming colliders.Comment: 11 pages, MadGraph home page at http://madgraph.physics.uiuc.ed
Lifetime statistics of quantum chaos studied by a multiscale analysis
In a series of pump and probe experiments, we study the lifetime statistics
of a quantum chaotic resonator when the number of open channels is greater than
one. Our design embeds a stadium billiard into a two dimensional photonic
crystal realized on a Silicon-on-insulator substrate. We calculate resonances
through a multiscale procedure that combines graph theory, energy landscape
analysis and wavelet transforms. Experimental data is found to follow the
universal predictions arising from random matrix theory with an excellent level
of agreement.Comment: 4 pages, 6 figure
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