Relic gravity waves from Braneworld inflation

Abstract

We discuss a scenario in which extra dimensional effects allow a scalar field with a steep potential to play the dual role of the inflaton as well as dark energy (quintessence). The post-inflationary evo- lution of the universe in this scenario is generically characterised by a ‘kinetic regime’ during which the kinetic energy of the scalar field greatly exceeds its potential energy resulting in a ‘stiff’ equa- tion of state for scalar field matter Pφ ≃ ρφ. The kinetic regime precedes the radiation dominated epoch and introduces an important new feature into the spectrum of relic gravity waves created quantum mechanically during inflation. The amplitude of the gravity wave spectrum increases with wavenumber for wavelengths shorter than the comoving horizon scale at the commencement of the radiative regime. This ‘blue tilt’ is a generic feature of models with steep potentials and imposes strong constraints on a class of inflationary braneworld models. Prospects for detection of the grav- ity wave background by terrestrial and space-borne gravity wave observatories such as LIGO II and LISA are discussed.