Probing The Dark Sector
Cosmology today is in a golden era, data is pouring in and exciting and challenging questions are being raised. We know that we live in an accelerating Universe populated largely by dark matter and dark energy, yet we have little information on the nature of either of these mysterious components. Theories abound and data is coming in with far greater quantity and precision than ever before and promises to enable distinguishing between these theories, however as we improve instruments we find ourselves plagued with how to effectively model signatures of the theories, and also how to truly interpret the data. Uncertainties in the nonlinear regime of theoretical predictions and in handling astrophysical systematics in observables are now emerging as leading issues that hinder constraining power. This thesis investigates the dark sector, considering first how one can approach the generation of correct nonlinear predictions for growth where gravity is modified (MG) in an attempt to explain the acceleration of the Universe. Next, we examine a possible Yukawa type self coupling of dark matter, motivated by the problems in small scale [LAMDA]CDM simulations of growth of structure, such as the cuspiness of halo density profiles and over production of small haloes. Finally, forecasts of constraining power for future surveys are made, in light of a key astrophysical systematic in weak lensing observations, namely the actual alignment of galaxies that form in the same halo which mixes in with the lensing signal in two ways, both generically summed up as Intrinsic Alignments(IA). We find that the standard approach of using fits developed in [LAMDA]CDM to generate nonlinear predicted matter power spectra for MG theories is valid, at least to mildly nonlinear scales. In the context of dark matter, there is no evidence against an interaction, yet also no preference for one. Finally for future survey forecasts, we find that previous forecasts were optimistic, and without a strong model for IA, additional probes will be required to compliment the weak lensing shear results and arrive at constraints similar to those derived from a survey in the absence of or with perfectly known IA contamination.
Cosmology; Weak lensing; Dark Matter; Dark Energy; Intrinsic Alignments; Fisher matrix
Bean, Rachel E.
Wasserman, Ira M; Flanagan, Eanna E; Herter, Terry Lee
Ph. D., Astronomy
Doctor of Philosophy
dissertation or thesis