1,430 research outputs found

    One loop corrections to coupling constants in String Effective Field Theory

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    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 Z2×Z2Z_2\times Z_2 orbifold model. The DD-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 FF 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

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    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

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    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 N=2N=2 ground states, namely those that are obtained by toroidal compactification to four dimensions of generic six-dimensional N=1N=1 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

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    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

    Rapidly reconfigurable optical phase encoder-decoders based on fiber Bragg gratings

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    We demonstrate the capacity for fast dynamic reconfiguration of optical code-division multiple access (OCDMA) phase en/decoders based on fiber Bragg gratings and a thermal phase-tuning technique. The tuning time between two different phase codes is measured to be less than 2 s. An OCDMA system using tunable-phase decoders is compared with a system using fixed-phase decoders and, although the system using fixed-phase decoders exhibits a shorter output autocorrelation pulsewidth and lower sidelobes, the system using tunable-phase decoders has advantages of flexibility and a more relaxed requirement on the input pulsewidth

    Editorial

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    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

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    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 (H2H_2), de Sitter branes (dS2_2), or anti-de-Sitter branes (AdS2_2). We explain that the dS2_2 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 AdS2×S2_2\times S^2 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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