Particle Physics Seminars at BNL

A New Symmetry of Cosmological Observables and a High Hubble Constant as an Indicator of a Mirror World Dark Sector

by Prof. Lloyd Knox (University of California Davis)


Finding cosmological models that are consistent with a wide range of observations, including those that indicate a high Hubble constant (the current rate of expansion of space), has proved to be very challenging. In this talk I explore why. Our exploration leads us to fundamental sources of length scales in cosmological models: gravitational collapse time scales and photon electron-scattering mean free paths. We find that scaling down these quantities leaves cosmic microwave background maps, and many other cosmological observables, nearly invariant, while boosting up the expansion rate. I then introduce a model that takes advantage of this symmetry to boost up model predictions of the Hubble constant given other cosmological data. Gravitational collapse time scales are scaled down from standard cosmological values by a `mirror world' dark sector and photon mean free paths are scaled down by reducing the amount of helium, thereby freeing up more electrons. I speculate about alternative ways to reduce photon mean free paths, as consistency with the Riess et al. (2021) measurement of the Hubble constant requires there to be less helium in the universe than is observed. 

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