We reconsider nonminimal $\lambda {\varphi }^4$ chaotic inflation which includes the gravitational coupling term $\xi \mathcal{R}{\varphi }^2$, where $\varphi$ denotes a gauge singlet inflaton field and $\mathcal{R}$ is the Ricci scalar. For $\xi \gg 1$, we require, following recent discussions, that the energy scale ${\lambda }^{1/4}{m}_P/\sqrt{\xi }$ for inflation should not exceed the effective UV cutoff scale $m_P/\xi$, where $m_P$ denotes the reduced Planck scale. The predictions for the tensor-to-scalar ratio $r$ and the scalar spectral index $n_s$ are found to lie within the Wilkinson Microwave Anisotropy Probe $1\mathrm{\text{−}}\sigma$ bounds for ${10}^{-12}\lesssim \lambda \lesssim {10}^{-4}$ and ${10}^{-3}\lesssim \xi \lesssim {10}^2$. In contrast, the corresponding predictions of minimal $\lambda {\varphi }^4$ chaotic inflation lie outside the Wilkinson Microwave Anisotropy Probe $2\mathrm{\text{−}}\sigma$ bounds. We also find that $r\gtrsim 0.002$, provided the scalar spectral index $n_s\ge 0.96$. In estimating the lower bound on $r$, we take into account possible modifications due to quantum corrections of the tree level inflationary potential.

• Received 4 June 2010

DOI:https://doi.org/10.1103/PhysRevD.82.043502