Tensor to scalar ratio in nonminimal φ4 inflation

We reconsider nonminimal λφ4 chaotic inflation which includes the gravitational coupling term ξRφ2, where φ denotes a gauge singlet inflaton field and R is the Ricci scalar. For ξ>>1, we require, following recent discussions, that the energy scale λ1/4mP/√(ξ) for inflation should not exceed the effective UV cutoff scale mP/ξ, where mP denotes the reduced Planck scale. The predictions for the tensor-to-scalar ratio r and the scalar spectral index ns are found to lie within the Wilkinson Microwave Anisotropy Probe 1-σ bounds for 10-12 < or approx. λ < or approx. 10-4 and 10-3 < or approx. ξ < or approx. 102. In contrast, the corresponding predictions of minimal λφ4 chaotic inflation lie outside the Wilkinson Microwave Anisotropy Probe 2-σ bounds. We also find that r > or approx. 0.002, provided the scalar spectral index ns≥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.