Power-law inflation with a nonminimally coupled scalar field

We consider the dynamics of power-law inflation with a nonminimally coupled scalar field φ. It is well known that multiple scalar fields with exponential potentials V(φ)=V₀ exp(-√16π/pm_pl²φ) lead to an inflationary solution even if each scalar field is not capable to sustain inflation. In this paper, we show that inflation can be assisted even in the one-field case by the effect of nonminimal coupling. When ξ is positive, since an effective potential which arises by a conformal transformation becomes flatter compared with the case of ξ =0 for φ>0, we have an inflationary solution even when the Universe evolves as noninflationary in the minimally coupled case. For negative ξ, the assisted inflation can take place when φ evolves in the region of φ<0.