Quantum noise and a low cosmic microwave background quadrupole

We propose a new scenario that cosmological density perturbation may originate from passive fluctuations of the inflaton during inflation. These fluctuations are driven dynamically by a colored quantum noise which is generated from the coupling of the inflaton to the quantum environment. They grow with time after the beginning of the inflation and become nearly scale-invariant at small scales. However, the larger-scale modes cross out the horizon earlier and do not have enough time to grow, thus resulting in a suppression of the density perturbation on large scales. This may explain the observed low quadrupole in the WMAP cosmic microwave background anisotropy data and potentially unveil the initial time of inflation