Insight into nucleon structure from generalized parton distributions

The lowest three moments of generalized parton distributions are calculated in full QCD and provide new insight into the behavior of nucleon electromagnetic form factors, the origin of the nucleon spin, and the transverse structure of the nucleon.Comment: 3 pages, Lattice2003(Theoretical developments

Moments of nucleon spin-dependent generalized parton distributions

We present a lattice measurement of the first two moments of the spin-dependent GPD H-tilde(x,xi,t). From these we obtain the axial coupling constant and the second moment of the spin-dependent forward parton distribution. The measurements are done in full QCD using Wilson fermions. In addition, we also present results from a first exploratory study of full QCD using Asqtad sea and domain-wall valence fermions.Comment: Lattice2003(Theory), 3 pages, 3 figures, to appear in the Proceedings of Lattice 200

Coherent photon bremsstrahlung and dynamics of heavy-ion collisions: comparison of different models

Differential spectra of coherent photon bremsstrahlung in relativistic heavy ion collisions are calculated within various schematic models of the projectile-target stopping. Two versions of the degradation length model, based on a phenomenological deceleration law, are considered. The simple shock wave model is studied analytically. The predictions of these models agree in the soft photon limit, where the spectrum is determined only by the final velocity distribution of charged particles. The results of these models in the case of central Au+Au collisions at various bombarding energies are compared with the predictions of the microscopic transport model UrQMD. It is shown that at the AGS energy the coherent photon bremsstrahlung exceeds the photon yield from $\pi^0$-decays at photon energies \omega\loo 50 MeV.Comment: 23 pages RevTeX, 9 eps Figure

The Fall of Stringy de Sitter

Kachru, Kallosh, Linde, & Trivedi recently constructed a four-dimensional de Sitter compactification of IIB string theory, which they showed to be metastable in agreement with general arguments about de Sitter spacetimes in quantum gravity. In this paper, we describe how discrete flux choices lead to a closely-spaced set of vacua and explore various decay channels. We find that in many situations NS5-brane meditated decays which exchange NSNS 3-form flux for D3-branes are comparatively very fast.Comment: 35 pp (11 pp appendices), 5 figures, v3. fixed minor typo

Moments of Nucleon Light Cone Quark Distributions Calculated in Full Lattice QCD

Moments of the quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD. Calculations of proton matrix elements of operators corresponding to these moments through the operator product expansion have been performed on $16^3 \times 32$ lattices for Wilson fermions at $\beta = 5.6$ using configurations from the SESAM collaboration and at $\beta = 5.5$ using configurations from SCRI. One-loop perturbative renormalization corrections are included. At quark masses accessible in present calculations, there is no statistically significant difference between quenched and full QCD results, indicating that the contributions of quark-antiquark excitations from the Dirac Sea are small. Close agreement between calculations with cooled configurations containing essentially only instantons and the full gluon configurations indicates that quark zero modes associated with instantons play a dominant role. Naive linear extrapolation of the full QCD calculation to the physical pion mass yields results inconsistent with experiment. Extrapolation to the chiral limit including the physics of the pion cloud can resolve this discrepancy and the requirements for a definitive chiral extrapolation are described.Comment: 53 Pages Revtex, 26 Figures, 9 Tables. Added additional reference and updated referenced data in Table I

Development and demonstration of atmospheric electricity hazards protection

An Advanced Development Program (ADP) to develop and demonstrate effective Atmospheric Electricity Hazards Protection (AEHP) for the fighter, transport/bomber, helicopter and cruise missile classes of air vehicles is being conducted under an Air Force Wright Aeronautical Laboratories (AFWAL) contract with Boeing Military Airplane Company (BMAC). Other Government agencies are also supporting the ADP. The parameters characterizing the lightning threat have been defined for moderate and severe flashes ; e.g., 200 kA peak and 200 kA/microsecond rise rate for the severe threat lightning current. The attachment of lightning flashes to aircraft has resulted in many losses of aircraft in the past. The losses have been caused by both physical damage to the aircraft frame or structure, and electrical effects to aircraft flight critical elements and systems. The losses associated with upset and/or damage may increase with the advent of sensitive integrated circuitry being used in flight critical applications, and the use of composite material in these airframes and structures thereby reducing its electromagnetic shielding effectiveness. Protection concepts ; e.g., circuit and system shielding, terminal protection, conducting floors and cable protection ; may be used to prevent damage. A design methodology considering airframe characteristics, and circuit and system characteristics and criticality, which will lead to identification of balanced protection schemes is presented. Incorporation of AEHP is expected to enhance the operational flexibility of air vehicles through increased confidence of all-weather operational integrity. The effectiveness demonstration phase of the AEHP ADP using a modified F-14 airframe with advanced avionic and power systems is described. An ACAP helicopter is also to be used as a testbed. The testbeds will be subjected to low-level continuous wave (CW), moderate-level pulse, and severe-level pulse current injection. This method evaluates the safety margin of the generic protection design.Un programme de développement avancé pour développer et démontrer l'efficacité de méthodes de protection contre les dangers de l'électricité atmosphérique pour les catégories de véhicules aériens du type avion de combat, avion de transport/bombardier, hélicoptère et missile de croisière est entrepris sous contrat de l'Air Force Wright Aeronautical Laboratories (AFWAL) par la Boeing Military Airplane Company (BMAC) ; d'autres agences gouvernementales apportent aussi leur soutien à ce programme. Les paramètres caractérisant la menace due à la foudre ont été définis pour des foudroiements modérés et des foudroiements sévères, ces derniers étant caractérisés par une amplitude crête de 200 kA et par une vitesse de montée de 200 kA par microseconde. Dans le passé l'attachement de la foudre aux aéronefs a produit de nombreuses pertes. Ces pertes ont été causées à la fois par les dommages physiques produits sur la structure de l'avion et par des effets électriques sur les éléments et systèmes jouant un rôle critique pour le vol de l'avion. Les pertes associées avec le déréglage et/ou le dommage ont tendance à s'accroître avec l'utilisation de circuits intégrés sensibles dans des applications critiques pour le vol, et avec l'utilisation de matériaux composites qui réduisent l'efficacité du blindage électromagnétique apporté par la structure. Pour éviter les dommages on peut utiliser différents concepts de protection : blindage des circuits et systèmes ; protection des sorties et des câbles ; planchers conducteurs. On présente ci-dessous une méthodologie au niveau de la conception qui tient compte des caractéristiques de la structure ainsi que des caractéristiques et du caractère critique des circuits et systèmes. Cette méthode doit conduire à l'identification de schémas de protection équilibrée. On attend de la mise en œuvre de l'AEHP qu'elle améliore la souplesse opérationnelle des véhicules aériens par un taux de confiance accru dans leur sécurité de fonctionnement au cours d'opérations tout-temps. Nous décrivons ci-dessous la phase de démonstration d'efficacité de l'AEHP ADP sur une cellule modifiée de F14 avec des systèmes avancés d'avionique et d'alimentation électrique. Un hélicoptère ACAP est aussi utilisé comme modèle d'essai. Le modèle d'essai sera soumis à des injections de courant sous forme d'une onde sinusoïdale à faible niveau, d'une impulsion à niveau modéré et d'une impulsion à fort niveau. Cette méthode permet d'évaluer le coefficient de sécurité des principes de protection retenus

Development and demonstration of atmospheric electricity hazards protection

An Advanced Development Program (ADP) to develop and demonstrate effective Atmospheric Electricity Hazards Protection (AEHP) for the fighter, transport/bomber, helicopter and cruise missile classes of air vehicles is being conducted under an Air Force Wright Aeronautical Laboratories (AFWAL) contract with Boeing Military Airplane Company (BMAC). Other Government agencies are also supporting the ADP. The parameters characterizing the lightning threat have been defined for moderate and severe flashes ; e.g., 200 kA peak and 200 kA/microsecond rise rate for the severe threat lightning current. The attachment of lightning flashes to aircraft has resulted in many losses of aircraft in the past. The losses have been caused by both physical damage to the aircraft frame or structure, and electrical effects to aircraft flight critical elements and systems. The losses associated with upset and/or damage may increase with the advent of sensitive integrated circuitry being used in flight critical applications, and the use of composite material in these airframes and structures thereby reducing its electromagnetic shielding effectiveness. Protection concepts ; e.g., circuit and system shielding, terminal protection, conducting floors and cable protection ; may be used to prevent damage. A design methodology considering airframe characteristics, and circuit and system characteristics and criticality, which will lead to identification of balanced protection schemes is presented. Incorporation of AEHP is expected to enhance the operational flexibility of air vehicles through increased confidence of all-weather operational integrity. The effectiveness demonstration phase of the AEHP ADP using a modified F-14 airframe with advanced avionic and power systems is described. An ACAP helicopter is also to be used as a testbed. The testbeds will be subjected to low-level continuous wave (CW), moderate-level pulse, and severe-level pulse current injection. This method evaluates the safety margin of the generic protection design