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Anomalies, the Dark Universe and Matter-Antimatter asymmetry

Nick E. Mavromatos (Natl. Tech. U. AthensKing's Coll. London)
Dec 2022
I review a (3+1)-dimensional, string-inspired cosmological model withgravitational anomalies (of Chern-Simons (CS) type) at early epochs, and atotally-antisymmetric torsion, dual to a massless axion-like field("gravitational axion"), which couples to the CS term. Under appropriateconditions, primordial gravitational waves can condense, leading to acondensate of the CS anomaly term. As a consequence, one obtains inflation inthis theory, of running-vacuum-model (RVM) type, without the need for externalinflatons. At the end of the inflationary era, chiral fermionic matter isgenerated, whose gravitational anomalies cancel the primordial ones. On theother hand, chiral anomalies of gauge type, which are also generated by thechiral matter, remain present during the post-inflationary epochs and becomeresponsible for the generation of a non-perturbative mass for thetorsion-related gravitational axion, which, in this way, might play the role ofa Dark Matter component of geometrical origin. Moreover, in this model, stringynon-perturbative effects during the RVM inflationary phase generate periodicstructures for the potential of axion-like particles that arise due tocompactification, and co-exist with the gravitational axions. Such periodicpotential modulations may lead to an enhanced production of primordial blackholes during inflation, which in turn affects the profile of the generatedgravitational waves during the radiation era, with potentially observableconsequences. This model also entails an unconventional mechanism forLeptogenesis, due to Lorentz-violating backgrounds of the gravitational axionsthat are generated during inflation, as a consequence of the anomalycondensates, and remain undiluted in the radiation era.