A Cosmological Window on Trans-Planckian Physics
  In the framework of inflation, scales which nowadays correspond to large scale structures were smaller than the Planck length at the beginning of inflation. Therefore, measurements of CMBR anisotropy or surveys of galaxies and of clusters of galaxies could help us to probe physics beyond the Planck scale. In these proceedings, we study how the inflationary observables depend on trans-Planckian physics. It is found that there exist cases where adiabaticity can be violated and the primordial spectrum of the quantum cosmological perturbations modified. These cases correspond to rather drastic alterations of the dispersion relation. There exist also modifications of the standard physics which leave the power spectrum unchanged and therefore which are compatible with the data. In this sense, the presently available observations already constrain trans-Planckian physics. 
Jerome Martin and Robert H. Brandenberger