Robustness of the inflationary perturbation spectrum to trans-Planckian physics

It is investigated if predictions of the inflationary scenario regarding spectra of scalar and tensor perturbations generated from quantum vacuum fluctuations are robust with respect to a modification of the dispersion law for frequencies beyond the Planck scale. For a large class of such modifications of special and general relativity, for which the WKB condition is not violated at super-high frequencies, the predictions remain unchanged. The opposite possibility is excluded by the absence of large amount of created particles due to the present Universe expansion. Creation of particles in the quantum state minimizing the energy density of a given mode at the moment of Planck boundary crossing is prohibited by the latter argument, too (contrary to creation in the adiabatic vacuum state which is very small now).