183,450 research outputs found

    On the Lie subalgebra of Killing-Milne and Killing-Cartan vector fields in Newtonian space-time

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    The Galilean (and more generally Milne) invariance of Newtonian theory allows for Killing vector fields of a general kind, whereby the Lie derivative of a field is not required to vanish but only to be cancellable by some infinitesimal Galilean (respectively Milne) gauge transformation. In this paper, it is shown that both the Killing-Milne vector fields, which preserve the background Newtonian space-time structure, and the Killing-Cartan vector fields, which in addition preserve the gravitational field, form a Lie subalgebra.Comment: 8 page

    Quantized gravitational waves in the Milne universe

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    The quantization of gravitational waves in the Milne universe is discussed. The relation between positive frequency functions of the gravitational waves in the Milne universe and those in the Minkowski universe is clarified. Implications to the one-bubble open inflation scenario are also discussed.Comment: 26 pages, 1 figure, revtex. submitted to Phys. Rev. D1

    Desingularization of the Milne Universe

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    Resolution of cosmological singularities is an important problem in any full theory of quantum gravity. The Milne orbifold is a cosmology with a big-bang/big-crunch singularity, but being a quotient of flat space it holds potential for resolution in string theory. It is known however, that some perturbative string amplitudes diverge in the Milne geometry. Here we show that flat space higher spin theories can effect a simple resolution of the Milne singularity when one embeds the latter in 2+1 dimensions. We explain how to reconcile this with the expectation that non-perturbative string effects are required for resolving Milne. Along the way, we introduce a Grassmann realization of the \.{I}n\"on\"u-Wigner contraction to export much of the AdS technology to our flat space computation.Comment: 4 pages, revtex, v2: minor clarifications/corrections, refs added, v3: minor error corrected, v4: published PLB version (essentially

    Milne boost from galilean gauge theory

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    Physical origin of Milne boost invariance of the Newton Cartan spacetime is traced to the effect of local Galilean boosts in its metric structure, using galilean gauge theory. Specifically, we do not require any gauge field to understand Milne boost invariance.Comment: Minor change, Matches published versio

    Milne-Eddington Solutions for Relativistic Plane-Parallel Flows

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    Radiative transfer in a relativistic plane-parallel flow, e.g., an accretion disk wind, is examined in the fully special relativistic treatment. Under the assumption of a constant flow speed, for the relativistically moving atmosphere we analytically obtain generalized Milne-Eddington solutions of radiative moment equations; the radiation energy density, the radiative flux, and the radiation pressure. In the static limit these solutions reduce to the traditional Milne-Eddington ones for the plane-parallel static atmosphere, whereas the source function nearly becomes constant as the flow speed increases. Using the analytical solutions, we analytically integrate the relativistic transfer equation to obtain the specific intensity. This specific intensity also reduces to the Milne-Eddinton case in the static limit, while the emergent intensity is strongly enhanced toward the flow direction due to the Doppler and aberration effects as the flow speed increases (relativistic peaking).Comment: 1o pages, 5 figure

    Stopping the Panzers: The Untold Story of D-Day (Book Review) by Marc Milner

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    Review of Stopping the Panzers: The Untold Story of D-Day by Marc Milne
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