11,812 research outputs found
Gravitational Lorentz Violations from M-Theory
In an attempt to bridge the gap between M-theory and braneworld
phenomenology, we present various gravitational Lorentz-violating braneworlds
which arise from p-brane systems. Lorentz invariance is still preserved locally
on the braneworld. For certain p-brane intersections, the massless graviton is
quasi-localized. This also results from an M5-brane in a C-field. In the case
of a p-brane perturbed from extremality, the quasi-localized graviton is
massive. For a braneworld arising from global AdS_5, gravitons travel faster
when further in the bulk, thereby apparently traversing distances faster than
light.Comment: 13 pages, 1 figure, LaTeX, references added, minor corrections and
addition
From the warm magnetized atomic medium to molecular clouds
{It has recently been proposed that giant molecular complexes form at the
sites where streams of diffuse warm atomic gas collide at transonic
velocities.} {We study the global statistics of molecular clouds formed by
large scale colliding flows of warm neutral atomic interstellar gas under ideal
MHD conditions. The flows deliver material as well as kinetic energy and
trigger thermal instability leading eventually to gravitational collapse.} {We
perform adaptive mesh refinement MHD simulations which, for the first time in
this context, treat self-consistently cooling and self-gravity.} {The clouds
formed in the simulations develop a highly inhomogeneous density and
temperature structure, with cold dense filaments and clumps condensing from
converging flows of warm atomic gas. In the clouds, the column density
probability density distribution (PDF) peaks at \sim 2 \times 10^{21} \psc
and decays rapidly at higher values; the magnetic intensity correlates weakly
with density from to 10^4 \pcc, and then varies roughly as
for higher densities.} {The global statistical properties of such
molecular clouds are reasonably consistent with observational determinations.
Our numerical simulations suggest that molecular clouds formed by the
moderately supersonic collision of warm atomic gas streams.}Comment: submitted to A&
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