Geometric Baryogenesis from Shift Symmetry

We present a new scenario for generating the baryon asymmetry of the Universe that is induced by a Nambu-Goldstone (NG) boson. The shift symmetry naturally controls the operators in the theory while allowing the NG boson to couple to the spacetime geometry as well as to the baryons. The cosmological background thus sources a coherent motion of the NG boson, which leads to baryogenesis. Good candidates of the baryon-generating NG boson are the QCD axion and axionlike fields. In these cases, the axion induces baryogenesis in the early Universe and can also serve as dark matter in the late Universe.

Figure 1

Parameter space in the $f-T_{\text{dec}}$ plane. The colored regions are excluded due to a significant backreaction from the baryons (red area) and by the Planck upper bound on the inflation scale (green area). The allowed parameter space is shown in white. The black lines indicate where the right amount of baryon asymmetry is produced, for the choice of $M=10^{18}$ (solid line), $10^{14}$ (dashed line), and $10^{10}\mathrm{GeV}$ (dotted line).