Boundary Inflation

TL;DR

This paper constructs inflationary solutions within a five-dimensional boundary model inspired by heterotic M-theory, analyzing linear and non-linear regimes and their implications for inhomogeneity and stability.

Contribution

It introduces new inflationary solutions in a five-dimensional boundary model, highlighting the role of boundary potentials and bulk Kaluza-Klein modes in the inflationary dynamics.

Findings

Linear regime allows effective 4D inflationary description

Existence of non-linear solutions with horizons or without

Issues with stability and initial mode excitations

Abstract

Inflationary solutions are constructed in a specific five-dimensional model with boundaries motivated by heterotic M-theory. We concentrate on the case where the vacuum energy is provided by potentials on those boundaries. It is pointed out that the presence of such potentials necessarily excites bulk Kaluza-Klein modes. We distinguish a linear and a non-linear regime for those modes. In the linear regime, inflation can be discussed in an effective four-dimensional theory in the conventional way. We lift a four-dimensional inflating solution up to five dimensions where it represents an inflating domain wall pair. This shows explicitly the inhomogeneity in the fifth dimension. We also demonstrate the existence of inflating solutions with unconventional properties in the non-linear regime. Specifically, we find solutions with and without an horizon between the two boundaries. These solutions have certain problems associated with the stability of the additional dimension and the persistence of initial excitations of the Kaluza-Klein modes.