Trans-Planckian physics from a nonlinear dispersion relation

We study a particular nonlinear dispersion relation {omega}{sub p}(k{sub p}) - a series expansion in the physical wave number k{sub p}--for modeling first-order corrections in the equation of motion of a test scalar field in a de Sitter spacetime from trans-Planckian physics in cosmology. Using both a numerical approach and a semianalytical one, we show that the WKB approximation previously adopted in the literature should be used with caution, since it holds only when the comoving wave number k>>aH. We determine the amplitude and behavior of the corrections on the power spectrum for this test field. Furthermore, we consider also a more realistic model of inflation, the power-law model, using only a numerical approach to determine the corrections on the power spectrum.