The Physics & Astronomy Colloquium Series presents Alex Krolewski of the University of Waterloo, discussing "Cosmology Beyond the Concordance Model? Testing Cosmological Tensions with Galaxy Surveys and Large Scale Structure" on Feburary 24.

Abstract: The Lambda-CDM model of the Universe dominated by dark matter and dark energy has been incredibly successful at matching diverse cosmological observations, but recent tensions could be hints of a breakdown in cosmological concordance.

In this talk I will describe efforts using galaxy and cosmic microwave background (CMB) surveys to test tensions in the growth of structure (S₈) and expansion rate of the Universe (H₀). Recently, cosmic shear surveys have measured a lower amplitude of structure (i.e. a less clumpy universe) than expected from precise measurements of CMB photons emitted by the hot early universe. Weak lensing of these CMB photons provides an alternative test of these measurements, free of many of their sources of systematic error. By cross-correlating 500 million infrared galaxies from unWISE with CMB lensing from ACT and Planck, we measure S₈ = 0.810 ± 0.015, fully consistent with the CMB. 

 I will also describe a new method for constraining the expansion rate (H₀) with large-scale structure that can address the Hubble tension between the CMB (favoring H₀ ~ 67 km s^-1 Mpc^-1) and local distance indicators (favoring H₀ ~ 73 km s^-1 Mpc^-1). We demonstrate this method with existing BOSS data, finding H₀ = 67.1 ± 5.8 km s^-1 Mpc^-1, and forecast that it can constrain H₀ to ~1.2 km s^-1 Mpc^-1 precision with Euclid and DESI. 

Finally, I conclude with a look to the future, describing my current and ongoing work within the DESI collaboration and the power of DESI in combination with upcoming CMB data from Simons Observatory and CMB-S4.