7 research outputs found
Regularization of static self-forces
Various regularization methods have been used to compute the self-force
acting on a static particle in a static, curved spacetime. Many of these are
based on Hadamard's two-point function in three dimensions. On the other hand,
the regularization method that enjoys the best justification is that of
Detweiler and Whiting, which is based on a four-dimensional Green's function.
We establish the connection between these methods and find that they are all
equivalent, in the sense that they all lead to the same static self-force. For
general static spacetimes, we compute local expansions of the Green's functions
on which the various regularization methods are based. We find that these agree
up to a certain high order, and conjecture that they might be equal to all
orders. We show that this equivalence is exact in the case of ultrastatic
spacetimes. Finally, our computations are exploited to provide regularization
parameters for a static particle in a general static and spherically-symmetric
spacetime.Comment: 23 pages, no figure
Absorption of dark matter by a supermassive black hole at the Galactic center: role of boundary conditions
The evolution of the dark matter distribution at the Galactic center is
analyzed, which is caused by the combination of gravitational scattering on
Galactic bulge stars and absorption by a supermassive black hole at the center
of the bulge. Attention is focused on the boundary condition on the black hole.
It is shown that its form depends on the energy of dark matter particles. The
modified flux of dark matter particles onto the black hole is calculated.
Estimates of the amount of dark matter absorbed show that the fraction of dark
matter in the total mass of the black hole may be significant. The density of
dark matter at the central part of the bulge is calculated. It is shown that
recently observed gamma radiation from the Galactic center can be attributed to
the annihilation of dark matter with this density.Comment: 5 page
A simple analytical model for dark matter halo structure and adiabatic contraction
A simple analytical model for describing inner parts of dark matter halo is
considered. It is assumed that dark matter density is power-law. The model
deals with dark matter distribution function in phase space of adiabatic
invariants (radial action and angular momentum). Two variants are considered
for the angular part of the distribution function: narrow and broad
distribution. The model allows to describe explicitly the process of adiabatic
contraction of halo due to change of gravitational potential caused by
condensation of baryonic matter in the centre. The modification of dark matter
density in the centre is calculated, and is it shown that the standard
algorithm of adiabatic contraction calculation overestimates the compressed
halo density, especially in the case of strong radial anisotropy.Comment: 5 pages, 3 figures. v3 - major improvements, another halo model
introduced, discussion extende