Possible origin of CMB temperature fluctuations: Vacuum fluctuations of Kaluza-Klein and string states during inflationary era

TL;DR

This paper proposes a novel mechanism for generating CMB temperature fluctuations through vacuum fluctuations of Kaluza-Klein and string states during inflation, especially when a large number of such fields are present.

Contribution

It introduces a new scenario where vacuum fluctuations of multiple fields contribute to CMB anisotropies, differing from the standard slow-roll inflation model.

Findings

Large number of fields enhances scalar perturbations

Model favors string scale around 10^{-5} of Planck scale

Mechanism can produce observed CMB fluctuation amplitudes

Abstract

We point out that the temperature fluctuations of cosmic microwave background (CMB) can be generated in a way that is different from the one usually assumed in slow-roll inflation. Our mechanism is based on vacuum fluctuations of fields which are at rest at the bottom of the potential, such as Kaluza-Klein modes or string excited states. When there are a large number (typically of order $N\sim 10^{14}$) of fields with small mass in unit of Hubble parameter during the inflationary era, this effect can give significant contributions to the CMB temperature fluctuations. This number $N$ makes it possible to enhance scalar perturbation relative to tensor perturbation. Comparison with the observed amplitudes suggests that models with string scale of order $10^{-5}$ of 4D Planck scale are favorable.