Tensor to scalar ratio in nonminimal φ4 inflation

We reconsider nonminimal lambda phi(4) chaotic inflation which includes the gravitational coupling term xi R phi(2), where phi denotes a gauge singlet inflaton field and R is the Ricci scalar. For xi >> 1, we require, following recent discussions, that the energy scale lambda(1/4)m(P)/root 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-sigma bounds for 10(-12) less than or similar to lambda less than or similar to 10(-4) and 10(-3) less than or similar to xi less than or similar to 10(2). In contrast, the corresponding predictions of minimal lambda phi(4) chaotic inflation lie outside the Wilkinson Microwave Anisotropy Probe 2-sigma bounds. We also find that r greater than or similar to 0.002, provided the scalar spectral index n(s) >= 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.