Topic 1: Potential new insights about reionization from the cosmic microwave background and the Lyman alpha forest Topic 2: Massive-neutrino Perturbations without the Boltzmann HierarchyTopic 1

Abstract 1: Reionization of the intergalactic medium remains one of the most mysterious questions in the research of cosmology. While the first generation of stars (Pop-III) likely ionize the universe at 1-10% level at z>15, the second generation of stars are believed to drive the bulk of reionization at z<12 and complete the reionization process in a patchy pattern. In this talk I will discuss potential new insights into Pop-III reionization at z>15 using the large-scale polarization of the CMB and imprints of patchy reionization at z<12 on the post-reionization Lyman-alpha forest. I will show that although future CMB surveys will be able to measure the large-scale CMB EE power spectrum at higher signal-to-noise and constrain the optical depth at z>15 much better than Planck, the detailed shape of the EE power spectrum is unlikely to add in more constraining power on our understanding of Pop-III star formation. On the other hand, temperature fluctuations owing to patchy reionization likely induce excess power on the large scales of the Lyman-alpha forest flux power spectrum, indicating a potential future observational constraint on the patchiness of reionization. We also found negligible impact of temperature fluctuations on the small-scale shape of the forest flux power spectrum, implying that patchy reionization is unlikely to bias current IGM temperature measurements and WDM/FDM constraints using the forest flux power spectrum.

Abstract 2: At the very foundation of many cosmology studies is a numerical algorithm that evolves the perturbations of matter and radiation from the Big Bang to today. This algorithm spends ~400 differential equations on the Boltzmann hierarchies of photons and 3 generations of massive neutrinos, in contrast to ~5 equations for the rest of the system (i.e. CDM+baryons). I will demonstrate how the line-of-sight integral can be used to replace the neutrino Boltzmann hierarchies, and present a new numerical scheme that can potentially accelerate the current state-of-the-art Boltzmann codes.