Visible and dark matter from a first-order phase transition in a baryon-symmetric universe

The similar cosmological abundances observed for visible and dark matter suggest a common origin for both. By viewing the dark matter density as a dark-sector asymmetry, mirroring the situation in the visible sector, we show that the visible and dark matter asyrnrnetries may have arisen simultaneously through a first-order phase transition in the early universe. The dark asymmetry can then be equal and opposite to the usual visible matter asymmetry, leading to a universe that is symmetric with respect to a generalised baryon number. We present both a general structure, and a precisely defined example of a viable model of this type. In that example, the dark matter is "atomic" as well as asymmetric, and various cosmological and astrophysical constraints are derived. Testable consequences for colliders include a Z' boson that couples through the B - L charge to the visible sector, but also decays invisibly to dark sector particles. The additional scalar particles in the theory can mix with the standard Higgs boson and provide other striking signatures.