Abstract
We describe a new mechanism — radiatively-induced gravitational leptogenesis — for generating the matter-antimatter asymmetry of the Universe. We show how quantum loop effects in C and CP violating theories cause matter and antimatter to propagate differently in the presence of gravity, and prove this is forbidden in flat space by CPT and translation symmetry. This generates a curvature-dependent chemical potential for leptons, allowing a matter-antimatter asymmetry to be generated in thermal equilibrium in the early Universe. The time-dependent dynamics necessary for leptogenesis is provided by the interaction of the virtual self-energy cloud of the leptons with the expanding curved spacetime background, which violates the strong equivalence principle and allows a distinction between matter and antimatter. We show here how this mechanism is realised in a particular BSM theory, the see-saw model, where the quantum loops involve the heavy sterile neutrinos responsible for light neutrino masses. We demonstrate by explicit computation of the relevant two-loop Feynman diagrams how the size of the radiative corrections relevant for leptogenesis becomes enhanced by increasing the mass hierarchy of the sterile neutrinos, and show how the induced lepton asymmetry may be sufficiently large to play an important role in determining the baryon-to-photon ratio of the Universe.
Highlights
Naturally exhibit our mechanism when minimally coupled to gravity, without the need to add new fundamental interactions
We describe a new mechanism — radiatively-induced gravitational leptogenesis — for generating the matter-antimatter asymmetry of the Universe
We demonstrate by explicit computation of the relevant two-loop Feynman diagrams how the size of the radiative corrections relevant for leptogenesis becomes enhanced by increasing the mass hierarchy of the sterile neutrinos, and show how the induced lepton asymmetry may be sufficiently large to play an important role in determining the baryon-to-photon ratio of the Universe
Summary
Our mechanism is very general, for clarity we illustrate it in this paper within a particular model — the see-saw model, first proposed as a means of obtaining a baryon asymmetry via leptogenesis by Fukugita and Yanagida [3]. Curved space two-loop self-energies which contribute to radiatively-induced gravitational leptogenesis In this way, a lepton asymmetry is generated at the point when the sterile neutrinos fall out of equilibrium. The time-dependent dynamics necessary to distinguish the dispersion relations for leptons and antileptons and induce the matter-antimatter asymmetry arises from the expansion of the Universe itself, through the gravitational coupling to the virtual self-energy cloud screening the leptons at the quantum loop level. The novel feature of our mechanism is that this sensitivity to the background arises dynamically, through explicitly quantum field theoretic effects occurring naturally at loop level This elucidates why the operator (1.5) responsible for the matterantimatter asymmetry depends on the non-vanishing of the time derivative of the curvature. Having highlighted some of the key similarities and differences between the traditional mechanism and our new approach, as embodied by the formulae (1.3) and (1.7) respectively, we spend the remainder of this paper examining in greater detail the origin of our effect, beginning with a discussion of propagation
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