1,181 research outputs found
One loop corrections to coupling constants in String Effective Field Theory
In the framework of a recently proposed method for computing exactly string
amplitudes regularized in the infra-red, I determine the one-loop correlators
for auxiliary fields in the symmetric orbifold model. The
-field correlation function turns out to give the one-loop corrections for
the gauge couplings, which amounts to a string-theory supersymmetry Ward
identity. The two-point function for uncharged fields leads to the one-loop
renormalization of the moduli K\"ahler metric, and eventually to the
corrections for the Yukawa couplings.Comment: Plain TeX, 19p
All-optical pulse reshaping and retiming systems incorporating pulse shaping fiber Bragg grating
This paper demonstrates two optical pulse retiming and reshaping systems incorporating superstructured fiber Bragg gratings (SSFBGs) as pulse shaping elements. A rectangular switching window is implemented to avoid conversion of the timing jitter on the original data pulses into pulse amplitude noise at the output of a nonlinear optical switch. In a first configuration, the rectangular pulse generator is used at the (low power) data input to a nonlinear optical loop mirror (NOLM) to perform retiming of an incident noisy data signal using a clean local clock signal to control the switch. In a second configuration, the authors further amplify the data signal and use it to switch a (low power) clean local clock signal. The S-shaped nonlinear characteristic of the NOLM results in this instance in a reduction of both timing and amplitude jitter on the data signal. The underlying technologies required for the implementation of this technique are such that an upgrade of the scheme for the regeneration of ultrahigh bit rate signals at data rates in excess of 320 Gb/s should be achievable
On the Heterotic Effective Action at One-Loop, Gauge Couplings and the Gravitational Sector
We present in detail the procedure for calculating the heterotic one-loop
effective action. We focus on gravitational and gauge couplings. We show that
the two-derivative couplings of the gravitational sector are not renormalized
at one loop when the ground state is supersymmetric. Arguments are presented
that this non-renormalization theorem persists to all orders in perturbation
theory. We also derive the full one-loop correction to the gauge coupling. For
a class of ground states, namely those that are obtained by toroidal
compactification to four dimensions of generic six-dimensional models, we
give an explicit formula for the gauge-group independent thresholds, and show
that these are equal within the whole family.Comment: LateX, 17pp. A minor correction mad
A reconfigurable optical header recognition system for optical packet routing applications
We demonstrate a reconfigurable all-optical packet processing system. The key device is a code-reconfigurable header decoder based on a fiber Bragg grating. The performance of the system is tested for different packet headers, and error-free operation is confirmed
Editorial
We use a linear FROG technique based on electro-optic modulation to fully characterise for the first time pulses from a 1.06 µm FP laser diode and design a grating to provide optimum pulse compression
Anti-de-Sitter D-branes
We study D-branes of the {SL(2,\bR)} WZW model, and of its discrete
orbifolds. Gluing the currents by group automorphisms leads to three types of
D-branes: two-dimensional hyperbolic planes (), de Sitter branes (dS),
or anti-de-Sitter branes (AdS). We explain that the dS branes are
unphysical, because the electric field on their worldvolume is supercritical.
By combining {SL(2,\bR)} and SU(2), we exhibit a class of supersymmetric
AdS three-brane worldvolumes, and consider their possible
embeddings in the near-horizon region of stringy black holes. We point out the
intriguing difference between the induced and the effective geometries of these
D-branes, and speculate on its possible significance.Comment: 34 pages, 6 eps figures, latex, uses JHEP.cls. Final version to
appear in JHEP. Minor corrections, and references adde
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