Eur. Phys. J. C (2016) 76: 26
https://doi.org/10.1140/epjc/s10052-016-3888-0

Regular Article - Theoretical Physics

Starobinsky-like two-field inflation

¹ Department of Physics, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachioji-shi, Tokyo, 192-0397, Japan
² Kavli Institute for the Physics and Mathematics of the Universe (IPMU), The University of Tokyo, Chiba, 277-8568, Japan
³ Institute of Physics and Technology, Tomsk Polytechnic University, 30 Lenin Ave., Tomsk, 634050, Russian Federation

^* e-mail: ketov@tmu.ac.jp

Received: 23 October 2015
Accepted: 7 January 2016
Published online: 20 January 2016

Abstract

We consider an extension of the Starobinsky model, whose parameters are functions of an extra scalar field. Our motivation is to test the robustness (or sensitivity) of the Starobinsky inflation against mixing scalaron with another (matter) scalar field. We find that the extended Starobinsky model is (classically) equivalent to the two-field inflation, with the scalar potential having a flat direction. For the sake of fully explicit calculations, we perform a numerical scan of the parameter space. Our findings support the viability of the Starobinsky-like two-field inflation for a certain range of its parameters, which is characterized by the scalar index , the tensor-to-scalar ratio , and a small running of the scalar index at .