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General theory of cosmological perturbations in open and closed universes from the Horndeski action

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arxiv 1810.01863 v1 pith:U54OV4FM submitted 2018-10-03 gr-qc hep-th

classification gr-qchep-th
keywords cosmologicaltheoryflatgeneralhorndeskiperturbationsspatiallycases
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abstract

Our Universe is nearly spatially flat, but this does not mean that it is exactly spatially flat. In this paper we derive general quadratic actions for cosmological perturbations in non-flat models from the Horndeski theory. This allows us to study how the spatial curvature influences the behavior of cosmological perturbations in the early universe described by some general scalar-tensor theory. We show that a tiny spatial curvature at the onset of inflation is unlikely to yield large (or ${\cal O}(1)$) effects on the primordial spectra even if one modifies gravity. We also argue that non-singular cosmological solutions in the Horndeski theory are unstable in spatially open cases as well as in flat cases.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem

    gr-qc 2019-08 conditional novelty 6.0 of 10

    In Horndeski gravity, matter bounce models can simultaneously satisfy the tensor-to-scalar ratio bound and non-Gaussianity constraints, evading a no-go theorem that applies to k-essence bounce models.

  2. Primordial black hole dark matter from ultra-slow-roll inflation in Horndeski gravity

    gr-qc 2025-12 conditional novelty 5.0 of 10

    A kinetic cubic Horndeski coupling creates an ultra-slow-roll phase that amplifies curvature perturbations enough to produce asteroid-mass primordial black holes, potentially 90% of dark matter.

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