title: Inflation driven by the Galileon field.
abstract: We propose a new class of inflation model, G inflation, which has a Galileon-like nonlinear derivative interaction of the form G(ϕ,(∇ϕ)(2))□ϕ in the Lagrangian with the resultant equations of motion being of second order. It is shown that (almost) scale-invariant curvature fluctuations can be generated even in the exactly de Sitter background and that the tensor-to-scalar ratio can take a significantly larger value than in the standard inflation models, violating the standard consistency relation. Furthermore, violation of the null energy condition can occur without any instabilities. As a result, the spectral index of tensor modes can be blue, which makes it easier to observe quantum gravitational waves from inflation by the planned gravitational-wave experiments such as LISA and DECIGO as well as by the upcoming CMB experiments such as Planck and CMBpol.
authors.affiliation: Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Masahide
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Jun'ichi
authors.initials: J
authors.lastname: Yokoyama