Abstract
Predictions of inflationary schemes can be influenced by the presence of extra dimensions. This could be of particular relevance for the spectrum of gravitational waves in models where the extra dimensions provide a brane-world solution to the hierarchy problem. Apart from models of large as well as exponentially warped extra dimensions, we analyze the size of tensor modes in the Linear Dilaton scheme recently revived in the discussion of the “clockwork mechanism”. The results are model dependent, significantly enhanced tensor modes on one side and a suppression on the other. In some cases we are led to a scheme of “remote inflation”, where the expansion is driven by energies at a hidden brane. In all cases where tensor modes are enhanced, the requirement of perturbativity of gravity leads to a stringent upper limit on the allowed Hubble rate during inflation.
Highlights
Up to now, work in this direction concentrated on a very specific picture, which we call the IRB assumption
Work in this direction concentrated on a very specific picture, which we call the IRB assumption. It assumes that inflation is driven by a field on our visible brane and assumes that radii of extra dimensions are fixed by a separate mechanism that does not influence the specific prediction of the inflationary scheme
Even though the discussion about the tensor modes in [1] is based on the IRB assumption that the inflaton field is confined to the visible brane, we remark that the result is applicable to general braneworld inflation including “remote inflation” where inflation is driven by an inflaton field located at the hidden brane
Summary
We are interested in five-dimensional “braneworld” scenarios where gravity is propagating in five dimensions, while the Standard Model is confined to a four-dimensional slice of spacetime. The (55) component of the Einstein equations, serves to determine the size of the 5th dimension independently of the details of the stabilization mechanism [25,26,27]. Considering matching conditions on the four-dimensional branes, this requires that L0,π is time independent [28], i.e. the energy densities are dominated by cosmological constants. This is a good assumption here, because we are interested in inflationary solutions of the scale factor a(t).
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