Eur. Phys. J. C (2015) 75: 344
https://doi.org/10.1140/epjc/s10052-015-3565-8

Regular Article - Theoretical Physics

Inflation in a conformally invariant two-scalar-field theory with an extra term

¹ Division of Human Support System, Faculty of Symbiotic Systems Science, Fukushima University, Fukushima, 960-1296, Japan
² Leading Graduate School Promotion Center, Ochanomizu University, Tokyo, 112-8610, Japan
³ Department of Physics, Graduate School of Humanities and Sciences, Ochanomizu University, Tokyo, 112-8610, Japan
⁴ Institut de Ciencies de lEspai (IEEC-CSIC), Campus UAB, Carrer de Can Magrans, s/n 08193 Cerdanyola del Valles, Barcelona, Spain
⁵ Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010, Barcelona, Spain
⁶ Joined Institute for Nuclear Research, Dubna, Moscow Region, Russia

^* e-mail: bamba@sss.fukushima-u.ac.jp

Received: 20 June 2015
Accepted: 8 July 2015
Published online: 23 July 2015

Abstract

We explore inflationary cosmology in a theory where there are two scalar fields which non-minimally couple to the Ricci scalar and an additional term, which breaks the conformal invariance. Particularly, we investigate the slow-roll inflation in the case of one dynamical scalar field and that of two dynamical scalar fields. It is explicitly demonstrated that the spectral index of the scalar mode of the density perturbations and the tensor-to-scalar ratio can be consistent with the observations obtaind by the recent Planck satellite. The graceful exit from the inflationary stage is achieved as in convenient gravity. We also propose the generalization of the model under discussion with three scalar fields.