Exploring extra dimensions through inflationary tensor modes

TL;DR

This paper investigates how extra dimensions influence inflationary tensor modes, revealing model-dependent effects that can enhance or suppress gravitational wave signals, with implications for the Hubble rate during inflation.

Contribution

It analyzes the impact of various extra-dimensional models, including the Linear Dilaton scheme, on inflationary tensor modes and their observational signatures.

Findings

Tensor modes can be significantly enhanced or suppressed depending on the model.

Enhanced tensor modes impose strict upper limits on the Hubble rate during inflation.

The study introduces the concept of 'remote inflation' driven by hidden brane energies.

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.