Dr. Keir Rogers (University of Toronto)

"A new five-sigma tension in the standard cosmological model: twenty years of growing evidence for new physics in the Lyman-alpha forest"

Abstract: Precision observations of the cosmos have established the concordance model of cosmology, but deep questions remain about the origin of cosmic structure and the fundamental nature of the dark sector. Further, significant discrepancies have arisen in the inference of basic model parameters: the Universe's expansion rate H_0 and matter clustering amplitude S_8. I will present the measurement of a new, five-sigma parameter tension between Planck cosmic microwave background and eBOSS Lyman-alpha forest data in their inference of the small-scale linear matter power spectrum (at wavenumber ~ 1 h/Mpc, redshift = 3). I will discuss resolutions to this tension either in populations of ultra-light axions (ULAs) or warm dark matter, or running in the primordial power spectrum which can inform us about the nature of cosmic inflation. The strong preference for power spectrum running that we find builds on twenty years of growing evidence from WMAP to Planck and SDSS-1 to eBOSS. I will also discuss potential Lyman-alpha forest systematics, in particular strong absorption systems, and the urgency needed to understand the source of this tension in light of imminent Dark Energy Spectroscopic Instrument analyses. Finally, I will discuss the context of this result in light of previous results demonstrating that ULAs also alleviate the S_8 tension — and upcoming complementary probes of the small-scale structure in Milky Way stellar streams.

Bio: I am a Dunlap Fellow at the University of Toronto working on cosmological tests of dark matter models -- and robust and efficient data analysis using statistical and machine learning methods. Previously, I worked at Stockholm University and completed my PhD at University College London.