Planck Scale Effects and Suppression of Power on the Large Scales in the Primordial Spectrum

By Shankaranarayanan Subramaniam, HEP Group, the Abdus Salam International Centre for Theoretical Physics (ICTP)

The enormous red-shifting of the modes during the inflationary epoch suggests that physics at the very high energy scales may modify the primordial perturbation spectrum. With the anisotropies in the Cosmic Microwave Background (CMB) being measured more and more accurately, it has been realized that, may be, we are on the threshold of observing Planck scale effects in the CMB. Motivated by this possibility, over the last few years, considerable amount of attention has been devoted to evaluating the Planckian corrections in the ultra-violet end of the inflationary perturbation spectrum. Most of these efforts have involved considering high energy models that violate Lorentz invariance locally. However, certain astrophysical observations seem to indicate that Lorentz invariance may be preserved to extremely high energies. In such a situation, to study the Planck scale effects, it becomes important to consider models that preserve Lorentz invariance even as they contain a fundamental scale. 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 {\it naturally}\/ predicts a suppression of power on large scales &em; a feature that seems to be necessary to explain lower power in the quadrupole and the octopole moments of the CMB. We find that the spectrum we obtain is very similar in form to the one that has recently been obtained from non-commutative inflation. Interestingly, 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.