We study nonlinear cosmological perturbations and their possible non-Gaussian character in an extended nonminimal inflation where gravity is coupled nonminimally to both the scalar field and its derivatives. By expansion of the action up to the third order, we focus on the nonlinearity and non-Gaussianity of perturbations in comparison with recent observational data. By adopting an inflation potential of the form 𝑉(𝜙) = (1/𝑛)𝜆𝜙𝑛, we show that, for 𝑛 = 4, for instance, this extended model is consistent with observation if 0.013 < 𝜆 < 0.095 in appropriate units. By restricting the equilateral amplitude of non-Gaussianity to the observationally viable values, the coupling parameter 𝜆 is constrained to the values 𝜆 < 0.1.
