Speaker: Francis-Yan Cyr-Racine, University of New Mexico
Abstract: Since they naturally live in angular and redshift space, astronomical observations have a built-in invariance under rescaling all length scales in the problem. Breaking this invariance requires the use of anchors, such as known distances or energy scales, that can set the absolute scale of the problem. These anchors are fundamental to our knowledge of cosmological distances throughout the Universe, and provide the backbone on which much of our knowledge of cosmology rests. These pillars have recently come under renewed scrutiny due to apparently discrepant measurements of the Hubble constant, a very important cosmological quantity which sets the size and age of the observable Universe. Here, we carefully examine the key anchors underpinning observations of the cosmic microwave background and baryon acoustic oscillations, finding ways to detach these measurements from their traditional anchors and fully restore their intrinsic scaling invariance. Not only can this help to understand the possible cause of the Hubble constant discrepancy, but it also sheds new light on the origins of cosmological constraints on new physics beyond the Standard Model. This in turn provides us with a general toolbox to design novel cosmological models that are automatically compatible with observations. The lessons we draw here about fundamental measurement anchors have broad applications outside of cosmology and astrophysics.