Two-point function for the Maxwell field in flat Robertson-Walker spacetimes

We obtain an explicit two-point function for the Maxwell field in flat Roberson-Walker spaces, thanks to a new gauge condition which takes the scale factor into account and assume a simple form. The two-point function is found to have the short distance Hadamard behavior.Comment: 4 pages, Revte

Massive scalar field on (A)dS space from a massless conformal field in R6\mathbb{R}^6

We show how the equations for the scalar field (including the massive, massless, minimally and conformally coupled cases) on de Sitter and Anti-de Sitter spaces can be obtained from both the SO$(2,4)$-invariant equation $\square \phi = 0$ in $\mathbb{R}^6$ and two geometrical constraints defining the (A)dS space. Apart from the equation in $\mathbb{R}^6$, the results only follow from the geometry.Comment: Revtex 4.1, 6 pages. In v3: New material added (references, relation with mass ladder operator), accepted in JM

Maximizing the Strength of Fused-Deposition ABS Plastic Parts

Fused-Deposition (FD) creates parts using robotic extrusion of set.D.i-liquid .polymer fiber, which molecularly bonds with neighboring fibers via thermal-dlffuslo.n bonding. T~e strength ofthe. part depends on the bulk polymer strength, themesostructure ~flber layout, vOid geom~try, extent of fiber bonding), and thefiber-t~-fiber ~ond strength. The ~nfluence of these factors on the mechanical strength of FD-ABS.plasttc parts IS reported.along with the.FD process variable settingsfor maximum strength. Substantial increases in transverse strength are achieved at the optirnal settings and additional increases can be achieved by post..fabrication annealing. Keywords: Stratasys, fused-deposition, ABSplastic, functional parts, strength, mesostructure, polymer diffusion.Mechanical Engineerin

Conformally covariant quantization of Maxwell field in de Sitter space

In this article, we quantize the Maxwell ("massless spin one") de Sitter field in a conformally invariant gauge. This quantization is invariant under the SO$_0(2,4)$ group and consequently under the de Sitter group. We obtain a new de Sitter invariant two-points function which is very simple. Our method relies on the one hand on a geometrical point of view which uses the realization of Minkowski, de Sitter and anti-de Sitter spaces as intersections of the null cone in \setR^6 and a moving plane, and on the other hand on a canonical quantization scheme of the Gupta-Bleuler type.Comment: v2 is is the definitive (improved compare to v1) versio

Examples of Berezin-Toeplitz Quantization: Finite sets and Unit Interval

We present a quantization scheme of an arbitrary measure space based on overcomplete families of states and generalizing the Klauder and the Berezin-Toeplitz approaches. This scheme could reveal itself as an efficient tool for quantizing physical systems for which more traditional methods like geometric quantization are uneasy to implement. The procedure is illustrated by (mostly two-dimensional) elementary examples in which the measure space is a $N$-element set and the unit interval. Spaces of states for the $N$-element set and the unit interval are the 2-dimensional euclidean $\R^2$ and hermitian \C^2 planes

Marine Mammals Inhabiting the Baffin Bay North Water in Winter

Aerial surveys in March-April 1978 and March 1979 showed that some species of marine mammals overwinter in isolated areas of open water in the North Water in northern Baffin Bay. About 700 walruses and 37 bearded seals were seen, most over deep water (200-500 m) near SE Ellesmere Island in March 1979. Both species were much less common in 1978. Approximately 500 belugas were found in recurrent leads along the edge of the fast-ice in eastern Jones and Lancaster sounds and, to a lesser extent, in Smith Sound. Only 12 narwhals were seen. It has been concluded that the North Water is not a major overwintering area for marine mammals

Conformally related massless fields in dS, AdS and Minkowski spaces

In this paper we write down the equation for a scalar conformally coupled field simultaneously for de Sitter (dS), anti-de Sitter (AdS) and Minkowski spacetime in d-dimensions. The curvature dependence appears in a very simple way through a conformal factor. As a consequence the process of curvature free limit, including wave functions limit and two-points functions, turns to be a straightforward issue. We determine a set of modes, that we call de Sitter plane waves, which become ordinary plane waves when the curvature vanishes.Comment: 7 pages, 1 figur

Constraints on cosmic-ray efficiency in the supernova remnant RCW 86 using multi-wavelength observations

Several young supernova remnants (SNRs) have recently been detected in the high-energy and very-high-energy gamma-ray domains. As exemplified by RX J1713.7-3946, the nature of this emission has been hotly debated, and direct evidence for the efficient acceleration of cosmic-ray protons at the SNR shocks still remains elusive. We analyzed more than 40 months of data acquired by the Large Area Telescope (LAT) on-board the Fermi Gamma-Ray Space Telescope in the HE domain, and gathered all of the relevant multi-wavelength (from radio to VHE gamma-rays) information about the broadband nonthermal emission from RCW 86. For this purpose, we re-analyzed the archival X-ray data from the ASCA/Gas Imaging Spectrometer (GIS), the XMM-Newton/EPIC-MOS, and the RXTE/Proportional Counter Array (PCA). Beyond the expected Galactic diffuse background, no significant gamma-ray emission in the direction of RCW 86 is detected in any of the 0.1-1, 1-10 and 10-100 GeV Fermi-LAT maps. In the hadronic scenario, the derived HE upper limits together with the HESS measurements in the VHE domain can only be accommodated by a spectral index Gamma <= 1.8, i.e. a value in-between the standard (test-particle) index and the asymptotic limit of theoretical particle spectra in the case of strongly modified shocks. The interpretation of the gamma-ray emission by inverse Compton scattering of high energy electrons reproduces the multi-wavelength data using a reasonable value for the average magnetic field of 15-25 muG. For these two scenarios, we assessed the level of acceleration efficiency. We discuss these results in the light of existing estimates of the magnetic field strength, the effective density and the acceleration efficiency in RCW 86.Comment: Accepted for publication in A&A; 10 pages and 4 figure