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.
CMB B-mode auto-bispectrum produced by primordial gravitational waves
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abstract
Gravitational waves from inflation induce polarization patterns in the cosmic microwave background (CMB). It is known that there are only two types of non-Gaussianities of the gravitaional waves in the most general scalar field theories having second-order field equations. One originates from the inherent non-Gaussianity in general relativity, and the other from a derivative coupling between the Einstein tensor and a kinetic term of the scalar field. We calculate polarization bispectra induced by these non-Gaussianities by transforming them into separable forms by virtue of the Laplace transformation. It is shown that future experiments can detect only the new one if the latter coupling parameter takes an extremely large value, which, however, does not cotradict the current observational data.
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gr-qc 1years
2019 1verdicts
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Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem
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.