Cosmological Perturbations from a New-Physics Hypersurface

Within a broad class of inflationary models we critically analyse the way initial quantum fluctuations on a new-physics hypersurface (NPH) affect standard predictions for large-scale cosmological perturbations. We find that these so-called trans-Planckian effects crucially depend on the definition of the 'vacuum state', in particular on which Hamiltonian is minimized on the NPH in order to select such a state. Trans-Planckian effects can be made much smaller than previously suggested if sufficiently 'adiabatic' Hamiltonians are minimized.