723 research outputs found
Numerical evolution of matter in dynamical axisymmetric black hole spacetimes. I. Methods and tests
We have developed a numerical code to study the evolution of self-gravitating
matter in dynamic black hole axisymmetric spacetimes in general relativity. The
matter fields are evolved with a high-resolution shock-capturing scheme that
uses the characteristic information of the general relativistic hydrodynamic
equations to build up a linearized Riemann solver. The spacetime is evolved
with an axisymmetric ADM code designed to evolve a wormhole in full general
relativity. We discuss the numerical and algorithmic issues related to the
effective coupling of the hydrodynamical and spacetime pieces of the code, as
well as the numerical methods and gauge conditions we use to evolve such
spacetimes. The code has been put through a series of tests that verify that it
functions correctly. Particularly, we develop and describe a new set of testbed
calculations and techniques designed to handle dynamically sliced,
self-gravitating matter flows on black holes, and subject the code to these
tests. We make some studies of the spherical and axisymmetric accretion onto a
dynamic black hole, the fully dynamical evolution of imploding shells of dust
with a black hole, the evolution of matter in rotating spacetimes, the
gravitational radiation induced by the presence of the matter fields and the
behavior of apparent horizons through the evolution.Comment: 42 pages, 20 figures, submitted to Phys Rev
Axion interpretation of the PVLAS data?
The PVLAS collaboration has recently reported the observation of a rotation
of the polarization plane of light propagating through a transverse static
magnetic field. Such an effect can arise from the production of a light, m_A ~
meV, pseudoscalar coupled to two photons with coupling strength g_{A\gamma} ~
5x10^{-6} GeV^{-1}. Here, we review these experimental findings, discuss how
astrophysical and helioscope bounds on this coupling can be evaded, and
emphasize some experimental proposals to test the scenario.Comment: 4 pages, 1 figure, jpconf.cls, talk presented at the ninth
International Conference on Topics in Astroparticle and Underground Physics,
TAUP 2005, Zaragoza, Spain, September 10-14, 200
Evading the astrophysical limits on light pseudoscalars
We study the possibility of evading astrophysical bounds on light
pseudoscalars. We argue that the solar bounds can be evaded if we have a
sufficiently strong self coupling of the pseudoscalars. The required couplings
do not conflict with any known experimental bounds. We show that it is possible
to find a coupling range such that the results of the recent PVLAS experiment
are not in conflict with any astrophysical bounds.Comment: 10 pages, 5 figures, minor change
Numerical evolution of matter in dynamical axisymmetric black hole spacetimes: I. Methods and tests
We have developed a numerical code to study the evolution of self-gravitating matter in dynamic black hole axisymmetric spacetimes in general relativity. The matter fields are evolved with a high-resolution shock-capturing scheme that uses the characteristic information of the general relativistic hydrodynamic equations to build up a linearized Riemann solver. The spacetime is evolved with an axisymmetric ADM code designed to evolve a wormhole in full general relativity. We discuss the numerical and algorithmic issues related to the effective coupling of the hydrodynamical and spacetime pieces of the code, as well as the numerical methods and gauge conditions we use to evolve such spacetimes. The code has been put through a series of tests that verify that it functions correctly. Particularly, we develop and describe a new set of testbed calculations and techniques designed to handle dynamically sliced, self-gravitating matter flows on black holes, and subject the code to these tests. We make some studies of the spherical and axisymmetric accretion onto a dynamic black hole, the fully dynamical evolution of imploding shells of dust with a black hole, the evolution of matter in rotating spacetimes, the gravitational radiation induced by the presence of the matter fields and the behavior of apparent horizons through the evolution
Self Interacting Dark Matter in the Solar System
Weakly coupled, almost massless, spin 0 particles have been predicted by many
extensions of the standard model of particle physics. Recently, the PVLAS group
observed a rotation of polarization of electromagnetic waves in vacuum in the
presence of transverse magnetic field. This phenomenon is best explained by the
existence of a weakly coupled light pseudoscalar particle. However, the
coupling required by this experiment is much larger than the conventional
astrophysical limits. Here we consider a hypothetical self-interacting
pseudoscalar particle which couples weakly with visible matter.
Assuming that these pseudoscalars pervade the galaxy, we show that the solar
limits on the pseudoscalar-photon coupling can be evaded.Comment: 17 pages, 2 figure
- …