The timescape cosmology represents a potentially viable alternative to
the standard homogeneous and isotropic Friedmann--Lemaître--Robertson--Walker (FLRW) cosmology,
without the need for dark energy. This thesis first extends the previous work on the
timescape cosmology to include a radiation component in the evolution equations for the
timescape cosmology and tests of the timescape model are then performed against the Cosmic
Microwave Background (CMB) temperature anisotropies from the Planck satellite.
Although
average cosmic evolution in the timescape scenario only differs substantially from that
of FLRW cosmologies at relatively late epochs
when the contribution from
the energy density of radiation is negligible, a full solution of the Buchert equations
to incorporate radiation is necessary to smoothly match parameters to the epoch
of photon decoupling and to obtain constraints from CMB
data. Here we have extended the matter-dominated solution found in earlier work to include
radiation, providing series solutions at early times and an efficient numerical integration
strategy for generating the complete solution.
To analyse the spectrum of CMB anisotropies in the timescape
cosmology we exploit the fact that the timescape cosmology is extremely close to the standard cosmology
at early epochs and adapt existing numerical codes to produce CMB anisotropy spectra. To find a
FLRW model that matches as closely as possible the timescape expansion history, we have studied and
compared a number of matching methods. We perform Markov Chain Monte Carlo analyses on the timescape model
parameter space,
and fit CMB multipoles 50 ≤ l ≤ 2500 to the Planck satellite data. Parameter fits include a dressed
Hubble constant, H₀ = 61.0 kms ⁻¹Mpc⁻¹ (±1.3% stat)(±8% sys), and a present void volume
fraction fᵥ₀ = 0.627 (±2.3% stat)(±13% sys). In the timescape model this
value of fᵥ₀ means that the galaxy/wall observer infers an accelerating universe,
where the apparent acceleration is due to gravitational energy gradients and clock rate differences rather than
some dark energy. We find best fit likelihoods which are comparable
to that of the best fit ΛCDM cosmology in the same multipole range.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/10199 |
| Date | January 2015 |
| Creators | Nazer, Mohammad Ahsan |
| Publisher | University of Canterbury. Physics and Astronomy |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Mohammad Ahsan nazer, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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