Robustness of the inflationary perturbation spectrum to trans-Planckian physics

Abstract

It is inspected whether the predictions of the inflationary scenario regarding the spectra of scalar and tensor perturbations generated by quantum vacuum fluctuations are robust with respect to the 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 ultrahigh frequencies, the predictions remain unchanged. The opposite possibility is excluded because of the absence of a large amount of particles created due to the Universe expansion. The creation of particles in the quantum state minimizing the energy density of a given mode at the moment of Planck boundary crossing is also prohibited by the latter argument (contrary to the creation in the adiabatic vacuum state, which is very small now).