Scale-invariant perturbations from NEC violation: A new variant of Galilean Genesis

Abstract

We propose a novel branch of the Galilean Genesis scenario as an alternative to inflation, in which the universe starts expanding from Minkowski in the asymptotic past with a gross violation of the null energy condition (NEC). This variant, described by several functions and parameters within the Horndeski scalar-tensor theory, shares the same background dynamics with the existing Genesis models, but the nature of primordial quantum fluctuations is quite distinct. In some cases, tensor perturbations grow on superhorizon scales. The tensor power spectrum can be red, blue, or scale invariant, depending on the model, while scalar perturbations are nearly scale invariant. This is in sharp contrast to typical NEC-violating cosmologies, in which a blue tensor tilt is generated. Though the primordial tensor and scalar spectra are both nearly scale invariant as in the inflationary scenario, the consistency relation in our variant of Galilean Genesis is non-standard.

10 pages, 4 figures; v2: published version

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Cited by in corpus (11)

• Horndeski theory and beyond: a review
• Intermittent null energy condition violations during inflation and primordial gravitational waves
• Broken blue-tilted inflationary gravitational waves: a joint analysis of NANOGrav 15-year and BICEP/Keck 2018 data
• Pulsar timing array observations as possible hints for nonsingular cosmology
• Cosmological consequences of a principle of finite amplitudes
• Toward evading the strong coupling problem in Horndeski genesis
• Nanohertz gravitational waves from NEC violation in the early universe
• Generating enhanced primordial GWs during inflation with intermittent violation of NEC and diminishment of GW propagating speed
• Improved DHOST Genesis
• Perturbative unitarity and NEC violation in genesis cosmology
• Primordial non-Gaussianity from Galilean Genesis without strong coupling problem