Multiscalar amplitudes to all orders in perturbation theory

A method for calculating loop amplitudes at the multiboson threshold is presented, based on Feynman-diagram techniques. We explicitly calculate the one-loop amplitudes in both $\phi^4$-symmetric and broken symmetry cases, using dimensional regularization. We argue that, to all orders in the perturbation expansion, the unitarity-violating behaviour of the tree-order amplitudes persists.Comment: 7 pages, Latex, CERN-TH.6852/9

On the nullification of threshold amplitudes

The nullification of threshold amplitudes is considered within the conventional framework of quantum field theory. The relevant Ward identities for the reduced theory are derived both on path-integral and diagrammatic levels. They are then used to prove the vanishing of tree-graph threshold amplitudes.Comment: 16 page

Reconstruction of Causal Networks by Set Covering

We present a method for the reconstruction of networks, based on the order of nodes visited by a stochastic branching process. Our algorithm reconstructs a network of minimal size that ensures consistency with the data. Crucially, we show that global consistency with the data can be achieved through purely local considerations, inferring the neighbourhood of each node in turn. The optimisation problem solved for each individual node can be reduced to a Set Covering Problem, which is known to be NP-hard but can be approximated well in practice. We then extend our approach to account for noisy data, based on the Minimum Description Length principle. We demonstrate our algorithms on synthetic data, generated by an SIR-like epidemiological model.Comment: Under consideration for the ECML PKDD 2010 conferenc

Nonperturbative bound on high multiplicity cross sections in phi^4_3 from lattice simulation

We have looked for evidence of large cross sections at large multiplicities in weakly coupled scalar field theory in three dimensions. We use spectral function sum rules to derive bounds on total cross sections where the sum can be expresed in terms of a quantity which can be measured by Monte Carlo simulation in Euclidean space. We find that high multiplicity cross sections remain small for energies and multiplicities for which large effects had been suggested.Comment: 23 pages, revtex, seven eps figures revised version: typos corrected, some rewriting of discusion, same resul

Zeroing in on more photons and gluons

We discuss radiation zeros that are found in gauge tree amplitudes for processes involving multi-photon emission. Previous results are clarified by examples and by further elaboration. The conditions under which such amplitude zeros occur are identical in form to those for the single-photon zeros, and all radiated photons must travel parallel to each other. Any other neutral particle likewise must be massless (e.g. gluon) and travel in that common direction. The relevance to questions like gluon jet identification and computational checks is considered. We use examples to show how certain multi-photon amplitudes evade the zeros, and to demonstrate the connection to a more general result, the decoupling of an external electromagnetic plane wave in the ``null zone". Brief comments are made about zeros associated with other gauge-boson emission.Comment: 26 page

Blood polymorphonuclear leukocyte chemotaxis during experimental escherichia-coli bovine mastitis.

The relationship between the severity of experimental Escherichia coli mastitis and the chemotactic response of blood polymorphonuclear leukocytes was investigated before and during mastitis. Experimental E. coli mastitis was induced in 10 healthy cows by inoculation of the rear right quarters with 10(3) cfu of E. coli. Cows were classified into two groups based on the severity of the mastitis. Bacterial growth in the inoculated quarter was used as parameter that indicated severity. Before and during experimental mastitis, the chemotactic response and the number of circulating polymorphonuclear leukocytes were greater for the moderately diseased cows than for the severely diseased cows. During the first 24 h of the experimental mastitis, the chemotactic response of polymorphonuclear leukocytes decreased in both groups. Recovery of the chemotactic response of white blood cells was more rapid in moderately diseased cows than in severely diseased cows. Possibly, the larger proportion of band neutrophils (the less chemotactically active band neutrophils) partially accounts for the lower chemotactic response of the circulating polymorphonuclear leukocytes during experimental mastitis in the severely diseased cows

The Nociceptin/Orphanin FQ Receptor Antagonist UFP-101 Reduces Microvascular Inflammation to Lipopolysaccharide In Vivo

Microvascular inflammation occurs during sepsis and the endogenous opioid-like peptide nociceptin/orphanin FQ (N/OFQ) is known to regulate inflammation. This study aimed to determine the inflammatory role of N/OFQ and its receptor NOP (ORL1) within the microcirculation, along with anti-inflammatory effects of the NOP antagonist UFP-101 (University of Ferrara Peptide-101) in an animal model of sepsis (endotoxemia). Male Wistar rats (220 to 300 g) were administered lipopolysaccharide (LPS) for 24 h (-24 h, 1 mg kg-1; -2 h, 1 mg kg-1 i.v., tail vein). They were then either anesthetised for observation of the mesenteric microcirculation using fluorescent in vivo microscopy, or isolated arterioles (~200 µm) were studied in vitro with pressure myography. 200 nM kg-1 fluorescently labelled N/OFQ (FITC-N/OFQ, i.a., mesenteric artery) bound to specific sites on the microvascular endothelium in vivo, indicating sparse distribution of NOP receptors. In vitro, arterioles (~200 µm) dilated to intraluminal N/OFQ (10-5M) (32.6 + 8.4%) and this response was exaggerated with LPS (62.0 +7.9%, p=0.031). In vivo, LPS induced macromolecular leak of FITC-BSA (0.02 g kg-1 i.v.) (LPS: 95.3 (86.7 to 97.9)%, p=0.043) from post-capillary venules (<40 µm) and increased leukocyte rolling as endotoxemia progressed (p=0.027), both being reduced by 150 nmol kg-1 UFP-101 (i.v., jugular vein). Firstly, the rat mesenteric microcirculation expresses NOP receptors and secondly, NOP function (ability to induce dilation) is enhanced with LPS. UFP-101 also reduced microvascular inflammation to endotoxemia in vivo. Hence inhibition of the microvascular N/OFQ-NOP pathway may have therapeutic potential during sepsis and warrants further investigation

Possibility of cyclic Turnarounds In Brane-world Scenario: Phantom Energy Accretion onto Black Holes and its consequences

A universe described by braneworlds is studied in a cyclic scenario. As expected such an oscillating universe will undergo turnarounds, whenever the phantom energy density reaches a critical value from either side. It is found that a universe described by RSII brane model will readily undergo oscillations if, either the brane tension, \lambda, or the bulk cosmological constant, \Lambda_{4}, is negative. The DGP brane model does not readily undergo cyclic turnarounds. Hence for this model a modified equation is proposed to incorporate the cyclic nature. It is found that there is always a remanent mass of a black hole at the verge of a turnaround. Hence contrary to known results in literature, it is found that the destruction of black holes at the turnaround is completely out of question. Finally to alleviate, if not solve, the problem posed by the black holes, it is argued that the remanent masses of the black holes do not act as a serious defect of the model because of Hawking evaporation.Comment: 10 pages, 2 figures; International Journal of Theoretical Physics (2012