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

TL;DR

The paper proposes a baryon-symmetric universe in which a generalised baryon number $B \equiv B_1 - B_2$ is conserved and the observed VM and DM densities arise from a common origin via a first-order phase transition in a generative sector that produces a shared $X$ asymmetry. This $X$ asymmetry is transferred to the visible and dark sectors, yielding equal and opposite $B-L$ asymmetries and a GeV-scale, atomic dark matter with a dark electromagnetism that self-assembles into neutral bound states. A gauged $B-L$ broken by a scalar keeps a global remnant to stabilize VM and DM, while a $Z'_{B-L}$ portal and an enriched scalar sector offer concrete collider and direct-detection signatures. The model remains compatible with BBN, dark recombination, and cluster constraints and motivates distinctive experimental tests at colliders and direct-detection experiments. Overall, it provides a coherent, testable mechanism linking the origins and properties of visible and dark matter through early-universe phase-transition dynamics.

Abstract

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 asymmetries 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.