Matter and Antimatter in the Universe

TL;DR

This paper surveys the matter–antimatter asymmetry in the early universe and the observational bounds on antimatter in the present cosmos, framing BAU in the context of Sakharov’s conditions and the limitations of the Standard Model. It reviews how BBN and the CMB/LSS measurements tightly constrain the baryon density, while considering the possibility of a large lepton asymmetry and its cosmological implications. The authors argue that the SM cannot account for the observed BAU and discuss a landscape of beyond‑SM theories, highlighting the νMSM (neutrino minimal Standard Model) as a minimal, experimentally testable scenario where sterile‑neutrino dynamics can simultaneously explain neutrino oscillations, dark matter, and BAU. The work emphasizes how upcoming experiments and observations could test these ideas, potentially linking baryogenesis to laboratory and astrophysical probes of sterile neutrinos and lepton asymmetries, with significant implications for particle physics and cosmology.

Abstract

We review observational evidence for a matter-antimatter asymmetry in the early universe, which leads to the remnant matter density we observe today. We also discuss observational bounds on the presence of antimatter in the present day universe, including the possibility of a large lepton asymmetry in the cosmic neutrino background. We briefly review the theoretical framework within which baryogenesis, the dynamical generation of a matter-antimatter asymmetry, can occur. As an example, we discuss a testable minimal model that simultaneously explains the baryon asymmetry of the universe, neutrino oscillations and dark matter.

Figures (2)

• Figure 1: An illustration of fermionic level crossing: The changing bosonic background fields can modify the fermionic energy levels, leading to fermion number violation when a level raises above the surface of the Dirac sea.
• Figure 2: Constraints on sterile neutrino mass $M$ and mixing $U^2={\rm tr}(\theta^\dagger \theta)$ in the $\nu$MSM as found in Canetti:2012khletter for normal (left panel) and inverted (right panel) hierarchy of active neutrino masses. In the regions below the black dashed "seesaw" line there exists no choice of $\nu$MSM parameters that is in accord with experimental constraints on the active neutrino mixing matrix. In the region below the black dotted BBN line, the lifetime of $N_{2,3}$ particles in the early universe is larger than $0.1$s, yielding the danger that their decay spoils the agreement between BBN calculations and observed light element abundances. The regions above the green lines of different shade are excluded by the NuTeV Vaitaitis:1999wq, CHARM Bergsma:1985is and CERN PS191 Bernardi:1985ny experiments, as indicated in the plot. In the region between the blue lines, a CP-asymmetry that explains the observed BAU can be produced during the thermal production of $N_{2,3}$. In the region within the red line, thermal production of $N_1$ (resonant and non-resonant) is sufficient to explain all observed DM. The CP-violating phases that maximise the efficiency of baryogenesis and DM production are different. They were chosen independently for the blue and red line displayed here. The region in which $\Omega_B$ and $\Omega_{DM}$ can be explained simultaneously almost coincides with the area inside the red line, see Canetti:2012kh.