A more complex dark sector?

UC Davis Physics and Astronomy graduate student Fei Ge just published his first paper and it's in Physical Review Letters as an "Editor's Suggestion." Fei, his advisor Lloyd Knox, and their collaborator Francis-Yan Cyr-Racine of the University of New Mexico point out in this paper a previously unnoticed symmetry of cosmological observables and then use that analytic understanding to address a discrepancy between predictions of the standard cosmological model and observations. To exploit the symmetry they make use of a "mirror world" -- a copy of the standard model of particle physics that only interacts very weakly with standard model particles. The paper title is "Symmetry of Cosmological Observables, a Mirror World Dark Sector, and the Hubble Constant." Reporting on the work, for lay audiences, is available in the California Aggie, the Egghead blog by Andy Fell, and the American Physical Society publication Physics