Abstract
Radiatively-induced gravitational leptogenesis is a potential mechanism to ex- plain the observed matter-antimatter asymmetry of the universe. Gravitational tidal effects at the quantum loop level modify the dynamics of the leptons in curved spacetime and may be encoded in a low-energy effective action Seff . It has been shown in previous work how in a high-scale BSM theory the CP odd curvature-induced interactions in Seff modify the dispersion relations of leptons and antileptons differently in an expanding universe, giving rise to an effective chemical potential and a non-vanishing equilibrium lepton-antilepton asymmetry. In this paper, the CP even curvature interactions are shown to break lepton number current conservation and modify the evolution of the lepton number density as the universe expands. These effects are implemented in a generalised Boltzmann equation and used to trace the dynamical evolution of the lepton number density in different cosmological scenarios. The theory predicts a potentially significant gravitationally-induced lepton-antilepton asymmetry at very early times in the evolution of the universe.
Highlights
The fundamental idea is that tidal gravitational effects at the quantum loop level can induce an asymmetry in the propagation of leptons and antileptons
It has been shown in previous work how in a high-scale Beyond the Standard Model (BSM) theory the CP odd curvature-induced interactions in Seff modify the dispersion relations of leptons and antileptons differently in an expanding universe, giving rise to an effective chemical potential and a non-vanishing equilibrium lepton-antilepton asymmetry
The direct curvature couplings in this Lagrangian effectively violate the strong equivalence principle, allowing gravity to distinguish between matter and antimatter. They are generated perturbatively at one and two-loop level in the standard model or, as required for realistic leptogenesis, a BSM theory characterised by a high mass scale M and exhibiting CP non-conservation, and can be understood qualitatively as the result of tidal gravitational forces acting on the extended cloud of virtual particles in the quantum loops
Summary
Where the spacetime curvature is sufficiently large, and a mechanism for lepton number violation. These are naturally incorporated in a BSM theory with three sterile neutrinos (i.e. having no interactions with the SM gauge fields) with a hierarchy of large Majorana masses, coupling to the usual left-handed leptons via the SM Higgs field. Of the question of leptogenesis, there are compelling reasons to augment the standard model in this way, with the see-saw mechanism explaining the existence of the non-zero masses of the light neutrinos
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