The statistical properties of dark matter (DM) on the largest scales in the universe are well described by the standard cosmological model. In contrast, comparatively little is known about the DM distribution within galaxies. I will discuss how early universe cosmological evolution and DM microphysics can result in enhanced structure, i.e. clumpiness, on sub-galactic scales. Using the examples...
It is shown (in spherical symmetry) that an exactly static black hole horizon cannot exist in an expanding universe. If you try to make it static in any dynamical ``background'', it becomes a naked spacetime singularity. This fact is demonstrated by the incompleteness of radial null and timelike geodesics, by the divergence of curvature invariants, the energy-momentum of a test scalar field,...
A novel vacuum (Riemann-flat) exact solution to the cosmological General Relativistic field equations has the feature that it is independent of the form of the cosmic scale factor. Spatial sections of this model solution are negatively curved and thus can mimic the acceleration of comoving observers attributed to dark energy. We perform a fit to the Union2.1 supernovae data set, yielding...
