18 research outputs found
Kinetic Theory of Collisionless Self-Gravitating Gases: II. Relativistic Corrections in Galactic Dynamics
In this paper we study the kinetic theory of many-particle astrophysical
systems imposing axial symmetry and extending our previous analysis in Phys.
Rev. D 83, 123007 (2011). Starting from a Newtonian model describing a
collisionless self-gravitating gas, we develop a framework to include
systematically the first general relativistic corrections to the matter
distribution and gravitational potentials for general stationary systems. Then,
we use our method to obtain particular solutions for the case of the Morgan &
Morgan disks. The models obtained are fully analytical and correspond to the
post-Newtonian generalizations of classical ones. We explore some properties of
the models in order to estimate the importance of post-Newtonian corrections
and we find that, contrary to the expectations, the main modifications appear
far from the galaxy cores. As a by-product of this investigation we derive the
corrected version of the tensor virial theorem. For stationary systems we
recover the same result as in the Newtonian theory. However, for time dependent
backgrounds we find that there is an extra piece that contributes to the
variation of the inertia tensor.Comment: 30 pages, 8 figures. v2: Minor corrections and references added.
Conclusions unchanged. v3: Version published in PR
Kinetic Theory of Collisionless Self-Gravitating Gases: Post-Newtonian Polytropes
In this paper we study the kinetic theory of many-particle astrophysical
systems and we present a consistent version of the collisionless Boltzmann
equation in the 1PN approximation. We argue that the equation presented by
Rezania and Sobouti in A&A 354 1110 (2000) is not the correct expression to
describe the evolution of a collisionless self-gravitating gas. One of the
reasons that account for the previous statement is that the energy of a
free-falling test particle, obeying the 1PN equations of motion for static
gravitational fields, is not a static solution of the mentioned equation. The
same statement holds for the angular momentum, in the case of spherical
systems. We provide the necessary corrections and obtain an equation that is
consistent with the corresponding equations of motion and the 1PN conserved
quantities. We suggest some potential relevance for the study of high density
astrophysical systems and as an application we construct the corrected version
of the post-Newtonian polytropes.Comment: 23 pages, 24 figures. Accepted for publication in PR
On the Beaming of Gluonic Fields at Strong Coupling
We examine the conditions for beaming of the gluonic field sourced by a heavy
quark in strongly-coupled conformal field theories, using the AdS/CFT
correspondence. Previous works have found that, contrary to naive expectations,
it is possible to set up collimated beams of gluonic radiation despite the
strong coupling. We show that, on the gravity side of the correspondence, this
follows directly (for arbitrary quark motion, and independently of any
approximations) from the fact that the string dual to the quark remains
unexpectedly close to the AdS boundary whenever the quark moves
ultra-relativistically. We also work out the validity conditions for a related
approximation scheme that proposed to explain the beaming effect though the
formation of shock waves in the bulk fields emitted by the string. We find that
these conditions are fulfilled in the case of ultra-relativistic uniform
circular motion that motivated the proposal, but unfortunately do not hold for
much more general quark trajectories.Comment: 1+33 pages, 2 figure