2,005 research outputs found

    Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun

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    We present a comparison between space charge calculations and direct measurements of the transverse phase space for space charge dominated electron bunches after a high voltage photoemission DC gun followed by an emittance compensation solenoid magnet. The measurements were performed using a double-slit setup for a set of parameters such as charge per bunch and the solenoid current. The data is compared with detailed simulations using 3D space charge codes GPT and Parmela3D with initial particle distributions created from the measured transverse and temporal laser profiles. Beam brightness as a function of beam fraction is calculated for the measured phase space maps and found to approach the theoretical maximum set by the thermal energy and accelerating field at the photocathode.Comment: 11 pages, 23 figures. submitted to Phys Rev ST-A

    Virtual photon structure functions and positivity constraints

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    We study the three positivity constraints among the eight virtual photon structure functions, derived from the Cauchy-Schwarz inequality and which are hence model-independent. The photon structure functions obtained from the simple parton model show quite different behaviors in a massive quark or a massless quark case, but they satisfy, in both cases, the three positivity constraints. We then discuss an inequality which holds among the unpolarized and polarized photon structure functions F1ÎłF_1^\gamma, g1Îłg_1^\gamma and WTTτW_{TT}^\tau, in the kinematic region Λ2â‰ȘP2â‰ȘQ2\Lambda^2\ll P^2 \ll Q^2, where −Q2(−P2)-Q^2 (-P^2) is the mass squared of the probe (target) photon, and we examine whether this inequality is satisfied by the perturbative QCD results.Comment: 24 pages, 13 eps figure

    Temperature Dependence of Extended and Fractional SU(3) Monopole Currents

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    We examine in pure SU(3) the dependence of extended monopole current k and cross-species extended monopole current k^{cross} on temperature t, monopole size L, and fractional monopole charge 1/q. We find that features of both k and k^{cross} are sensitive to t for a range of L and q. In particular, the spatial-temporal asymmetry ratios of both k and k^{cross} are sensitive over a range of L and q to the SU(3) deconfinement transition. The motivation for studying cross, extended, and fractional monopoles in SU(3) is given.Comment: 15 pages (archiving final publication version; very minor revisions

    Volume Expansion of Swiss-Cheese Universe

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    In order to investigate the effect of inhomogeneities on the volume expansion of the universe, we study modified Swiss-Cheese universe model. Since this model is an exact solution of Einstein equations, we can get an insight into non-linear dynamics of inhomogeneous universe from it. We find that inhomogeneities make the volume expansion slower than that of the background Einstein-de Sitter universe when those can be regarded as small fluctuations in the background universe. This result is consistent with the previous studies based on the second order perturbation analysis. On the other hand, if the inhomogeneities can not be treated as small perturbations, the volume expansion of the universe depends on the type of fluctuations. Although the volume expansion rate approaches to the background value asymptotically, the volume itself can be finally arbitrarily smaller than the background one and can be larger than that of the background but there is an upper bound on it.Comment: 22 pages, 7 figures, to be submitted to Phys. Rev.

    Polarized Virtual Photon Structure Function g2Îłg_2^\gamma and Twist-3 Effects in QCD

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    We investigate the twist-3 effects in the polarized virtual photon structure. The structure functions g1γg_1^\gamma and g2γg_2^\gamma of polarized photon could be experimentally studied in the future polarized epep or e+e−e^+e^- colliders. The leading contributions to g1γg_1^\gamma are the twist-2 effects, while another structure function g2γg_2^\gamma, which only exists for the virtual photon target, receives not only the twist-2 but also twist-3 contributions. We first show that the twist-3 effects actually exist in the box-diagram contributions and we extract the twist-3 part, which can also be reproduced by the pure QED operator product expansion. We then calculate the non-trivial lowest moment (n=3n=3) of the twist-3 contribution to g2γg_2^\gamma in QCD. For large NcN_c (the number of colors), the QCD analysis of the twist-3 effects in the flavor nonsinglet part of g2γg_2^\gamma becomes tractable and we can obtain its moments in a compact form for all nn.Comment: 27 pages, LaTeX, 9 eps figures, eqsection.sty file included, Appendix A added, some minor changes for Fig.

    Associations between paternally transmitted fetal IGF2 variants and maternal circulating glucose concentrations in pregnancy.

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    OBJECTIVE: To test the hypothesis that polymorphic variation in the paternally transmitted fetal IGF2 gene is associated with maternal glucose concentrations in the third trimester of pregnancy. RESEARCH DESIGN AND METHODS: A total of 17 haplotype tag single nucleotide polymorphisms in the IGF2 gene region were genotyped in 1,160 mother/partner/offspring trios from the prospective Cambridge Baby Growth Study (n = 845 trios) and the retrospective Cambridge Wellbeing Study (n = 315 trios) (3,480 samples in total). Associations were tested between inferred parent-of-origin fetal alleles, z scores of maternal glucose concentrations 60 min. after an oral glucose load performed at week 28 of pregnancy, and offspring birth weights. RESULTS: Using the minimum P value test, paternally transmitted fetal IGF2 polymorphisms were associated with maternal glucose concentrations; specifically, paternally transmitted fetal rs6578987 (P = 0.006), rs680 (P = 0.01), rs10770125 (P = 0.0002), and rs7924316 (P = 0.01) alleles were associated with increased maternal glucose concentrations in the third trimester of pregnancy and placental IGF-II contents at birth (P = 0.03). In contrast, there were no associations between maternal glucose concentrations and maternal or maternally transmitted fetal IGF2 genotypes. CONCLUSIONS: Polymorphic variation in paternally transmitted fetal IGF2 is associated with increased maternal glucose concentrations in pregnancy and could potentially alter the risk of gestational diabetes in the mother. The association may be at least partially mediated by changes in placental IGF2 expression

    Target Mass Effects in Polarized Virtual Photon Structure Functions

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    We study target mass effects in the polarized virtual photon structure functions g1Îł(x,Q2,P2)g_1^\gamma (x,Q^2,P^2), g2Îł(x,Q2,P2)g_2^\gamma (x,Q^2,P^2) in the kinematic region Λ2â‰ȘP2â‰ȘQ2\Lambda^2\ll P^2 \ll Q^2, where −Q2(−P2)-Q^2 (-P^2) is the mass squared of the probe (target) photon. We obtain the expressions for g1Îł(x,Q2,P2)g_1^\gamma (x,Q^2,P^2) and g2Îł(x,Q2,P2)g_2^\gamma (x,Q^2,P^2) in closed form by inverting the Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis shows that target mass effects appear at large xx and become sizable near xmax(=1/(1+P2Q2))x_{\rm max}(=1/(1+\frac{P^2}{Q^2})), the maximal value of xx, as the ratio P2/Q2P^2/Q^2 increases. Target mass effects for the sum rules of g1Îłg_1^\gamma and g2Îłg_2^\gamma are also discussed.Comment: 24 pages, LaTeX, 9 eps figure

    Vertex Operators in 4D Quantum Gravity Formulated as CFT

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    We study vertex operators in 4D conformal field theory derived from quantized gravity, whose dynamics is governed by the Wess-Zumino action by Riegert and the Weyl action. Conformal symmetry is equal to diffeomorphism symmetry in the ultraviolet limit, which mixes positive-metric and negative-metric modes of the gravitational field and thus these modes cannot be treated separately in physical operators. In this paper, we construct gravitational vertex operators such as the Ricci scalar, defined as space-time volume integrals of them are invariant under conformal transformations. Short distance singularities of these operator products are computed and it is shown that their coefficients have physically correct sign. Furthermore, we show that conformal algebra holds even in the system perturbed by the cosmological constant vertex operator as in the case of the Liouville theory shown by Curtright and Thorn.Comment: 26 pages, rewrote review part concisely, added explanation

    Thick domain walls around a black hole

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    We discuss the gravitationally interacting system of a thick domain wall and a black hole. We numerically solve the scalar field equation in the Schwarzschild spacetime and obtain a sequence of static axi-symmetric solutions representing thick domain walls. We find that, for the walls near the horizon, the Nambu--Goto approximation is no longer valid.Comment: 18 pages, 11 figures, one reference adde
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