The open inflation model recently proposed by Hawking and Turok is investigated in scalar-tensor gravity context. If the dilaton-like field has no potential, the instanton of our model is singular but has a finite action. The GibbonsHawking surface term vanishes and hence, can not be used to make Ω 0 nonzero.To obtain a successful open inflation one should introduce other matter fields or a potential for the dilaton-like fields.PACS numbers: 98.80.Cq 1
We study slow-roll inflation with a Gauss-Bonnet term that is coupled to an inflaton field nonminimally. We investigate the inflationary solutions for a specific type of the nonminimal coupling to the GaussBonnet term and inflaton potential both analytically and numerically. We also calculate the observable quantities such as the power spectra of the scalar and tensor modes, the spectral indices, the tensor-to-scalar ratio, and the running spectral indices. Finally, we constrain our result with the observational data by Planck and BICEP2 experiment.
We investigate the linear cosmological perturbations in Hořava-Lifshitz gravity with a scalar field. Starting from the most general expressions of the metric perturbations as well as that of a canonical scalar field, we decompose the scalar, vector and tensor parts of the perturbed action.By reducing the Hamiltonian, we find that there are two independent degrees of freedom for the tensor perturbations while none for the vector perturbations. For the scalar perturbations, the remaining number of degrees of freedom, which are all gauge invariant, depends on whether the projectable condition is applied or not: two when applied, with one of them being possibly a ghost, and one when not applied. For both cases, we lose the time reparametrization symmetry of any kind.
We study inflationary models with a Gauss-Bonnet term to reconstruct the scalar field potentials and the Gauss-Bonnet coupling functions from the observable quantities. Using the observationally favored relations for both n s and r, we derive the expressions for both the scalar field potentials and the coupling functions. The implication of the blue-tilted spectrum, n t > 0, of the primordial tensor fluctuations is discussed for the reconstructed configurations of the scalar field potential and the Gauss-Bonnet coupling.
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