Cosmological observables in the quasi-spherical Szekeres model

Buckley, Robert G.
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The standard model of cosmology presents a homogeneous universe, and we interpret cosmological data through this framework. However, structure growth creates nonlinear inhomogeneities that may affect observations, and even larger structures may be hidden by our limited vantage point and small number of independent observations. As we determine the universe's parameters with increasing precision, the accuracy is contingent on our understanding of the effects of such structures. For instance, giant void models can explain some observations without dark energy. Because perturbation theory cannot adequately describe nonlinear inhomogeneities, exact solutions to the equations of general relativity are important for these questions. The most general known solution capable of describing inhomogeneous matter distributions is the Szekeres class of models. In this work, we study the quasi-spherical subclass of these models, using numerical simulations to calculate the inhomogeneities' effects on observations. We calculate the large-angle CMB in giant void models and compare with simpler, symmetric void models that have previously been found inadequate to matchobservations. We extend this by considering models with early-time inhomogeneities as well. Then, we study distance observations, including selection effects, in models which are homogeneous on scales around 100 Mpc--consistent with standard cosmology--but inhomogeneous on smaller scales. Finally, we consider photon polarizations, and show that they are not directly affected by inhomogeneities. Overall, we find that while Szekeres models have some advantages over simpler models, they are still seriously limited in their ability to alter our parameter estimation while remaining within the bounds of current observations.

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Cosmic Microwave Background, Cosmology, Dark Energy, General relativity, Inhomogeneous universe models, Large scale structure
Physics and Astronomy