183,450 research outputs found
On the Lie subalgebra of Killing-Milne and Killing-Cartan vector fields in Newtonian space-time
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
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
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
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
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
Review of Stopping the Panzers: The Untold Story of D-Day by Marc Milne
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