Trans-Planckian corrections to the primordial spectrum in the infra-red   and the ultra-violet
  Due to the tremendous red-shift that occurs during the inflationary epoch in the early universe, it has been realized that trans-Planckian physics may manifest itself at energies much lower than the Planck energy. The presence of a fundamental scale suggests that local Lorentz invariance may be violated at sufficiently high energies. Motivated by this possibility, recently, different models that violate Lorentz invariance locally have been used to evaluate the trans-Planckian corrections to the inflationary density perturbation spectrum. However, certain astrophysical observations seem to indicate that local Lorentz invariance may be preserved to extremely high energies. In such a situation, to study the trans-Planckian effects, it becomes imperative to consider models that preserve local Lorentz invariance even as they contain a fundamental scale. In this work, we construct one such model and evaluate the resulting spectrum of density perturbations in the power-law inflationary scenario. While our model reproduces the standard spectrum on small scales, it naturally predicts a suppression of power on large scales. In fact, the spectrum we obtain has some features which are similar to the one that has recently been obtained from non-commutative inflation. However, we find that the amount of suppression predicted by our model is far less than that is required to fit the observations. We comment on the fact that, with a suitable choice of initial conditions, our approach can lead to corrections at the infra-red as well as at the ultra-violet ends of the spectrum. 
S. Shankaranarayanan (ICTP, Trieste) and L. Sriramkumar (HRI,   Allahabad)