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UBC Theses and Dissertations

Searching for hemispheric asymmetry and parity violation with the cosmic microwave background Contreras, Dagoberto


The current standard model of cosmology is an extremely successful theory that describes all available data with only half a dozen or so parameters. Nevertheless there are aspects of the model that remain mysterious. In this thesis I test two assumptions with the cosmic microwave background (CMB) as measured by the Planck satellite mission. The first is statistical isotropy, motivated by hints in the temperature anisotropies that power on large scales exhibits a dipolar asymmetry. I confront this claim with data and formulate a mechanism to predict the corresponding asymmetry in different modes given a specific model. I apply this to temperature, CMB lensing, and polarization specifically. I find that while lensing is not constraining enough to help in distinguishing models, cosmic-variance-limited polarization will prove very helpful in doing so. I forecast that if the asymmetry signal is correct, then Planck polarization is quite unlikely to detect it, while a cosmic-variance-limited polarization experiment will increase the probability of a detection greatly. Furthermore via their over production of total power to the CMB, I rule out a class of models that try to explain the asymmetry such as an asymmetry in tensors or isocurvature. The second assumed symmetry is parity. The CMB is sensitive to parity-violation in the electromagnetic sector via correlations of temperature and E modes with B modes. The parity-violation is parameterized by an angle ⍺, defined on the sky. I use polarization data to constrain a uniform ⍺, setting the current best limits on this angle ⍺ = 0°.35 ± 0°.05 (stat.) ± 0°.28 (syst.). I demonstrate that this measurement is now dominated by systematic effects and thus unlikely to be improved upon in the near future. I also set the current best constraints on large-scale anisotropies of ⍺ via a scale-invariant power spectrum l(l+1)CL/2π < [2.2 (stat.) ± 0.7 (syst.)] × 10⁻⁵ = [0.07 (stat.) ± 0.02 (syst.)] deg². Furthermore I constrain power on l = 1, √(3C₁/4π) = 0°.32 ± 0°.10 (stat.) ± 0°.08 (syst.) and l=2 modes ⍺₂₀ = 0°.02 ± 0°.21. The CMB is therefore consistent with no parity violations.

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