6 research outputs found
Cosmological backreaction in the presence of radiation and a cosmological constant
V. A. A. S. and T. C. both acknowledge support from
the STFC
The magnetic part of the Weyl tensor, and the expansion of discrete universes
42 pages, 27 figures42 pages, 27 figures42 pages, 27 figures42 pages, 27 figures42 pages, 27 figures42 pages, 27 figuresTC is supported by the STFC and DG by an AARMS postdoctoral fellowship
Cosmological solutions with charged black holes
RB aknowledges support from the Higher Education Commission (HEC) of Pakistan, which provided funding to visit QMUL while this work was performed. TC and JD are supported by the STFC
Ray tracing and Hubble diagrams in post-Newtonian cosmology
On small scales the observable Universe is highly inhomogeneous, with
galaxies and clusters forming a complex web of voids and filaments. The optical
properties of such configurations can be quite different from the perfectly
smooth Friedmann-Lema\^itre-Robertson-Walker (FLRW) solutions that are
frequently used in cosmology, and must be well understood if we are to make
precise inferences about fundamental physics from cosmological observations. We
investigate this problem by calculating redshifts and luminosity distances
within a class of cosmological models that are constructed explicitly in order
to allow for large density contrasts on small scales. Our study of optics is
then achieved by propagating one hundred thousand null geodesics through such
space-times, with matter arranged in either compact opaque objects or diffuse
transparent haloes. We find that in the absence of opaque objects, the mean of
our ray tracing results faithfully reproduces the expectations from FLRW
cosmology. When opaque objects with sizes similar to those of galactic bulges
are introduced, however, we find that the mean of distance measures can be
shifted up from FLRW predictions by as much as . This bias is due to the
viable photon trajectories being restricted by the presence of the opaque
objects, which means that they cannot probe the regions of space-time with the
highest curvature. It corresponds to a positive bias of order in the
estimation of and highlights the important consequences that
astronomical selection effects can have on cosmological observables.Comment: 37 pages, 15 figures, 1 table, v2: matches published versio