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Shinsuke Kawai
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Gravitational wave leptogenesis
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The gravitational Chern-Simons term coupled
to an evolving axion is known to generate
lepton number through the gravitational anomaly.
We examine this leptogenesis scenario in
the presence of the Gauss-Bonnet term over
and above the gravitational Chern-Simons
term. We find that the lepton production
can be exponentially enhanced. The Gauss-Bonnet
term creates CP-violating instability of
gravitational waves that may appear transiently
after inflation, and during the period of
instability elliptically polarized gravitational
waves are exponentially amplified at sub-horizon
scales. This instability does not affect
the spectrum of the cosmic microwave background
as it occurs at much shorter length scales.
In a typical scenario based on natural inflation,
the observed baryon asymmetry of the Universe
corresponds to the UV cutoff scale at 10^14−10^16
GeV [based on arXiv:1702.07689]
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