Fingerprints of Primordial Universe Paradigms as Features in Density Perturbations

Abstract

Experimentally distinguishing different primordial universe paradigms that lead to the Big Bang model is an outstanding challenge in modern cosmology and astrophysics. We show that a generic type of signals that exist in primordial universe models can be used for such purpose. These signals are induced by tiny oscillations of massive fields and manifest as features in primordial density perturbations. They are capable of recording the time-dependence of the scale factor of the primordial universe, and therefore provide direct evidence for specific paradigm.

Figures (2)

• Figure 1: The first type of fingerprints for different paradigms: multiple oscillations. From top to bottom: $p=10$ (inflation), $p=2/3$ (matter contraction), $p=0.2$ (Ekpyrosis), $p=-0.2$ (slow expansion). The red/dark spectra correspond to $m_\sigma/H = 10,20,120$ excited by a common sharp feature; the green/ligh spectra correspond to $m_\sigma/H=30,150$ excited by another common sharp feature.
• Figure 2: The second type of fingerprints for different paradigms: in conjunction with sharp feature. From top to bottom: $p=10$ (inflation), $p=2/3$ (matter contraction), $p=0.2$ (Ekpyrosis), $p=-0.2$ (slow expansion). The Green/light spectra are generated by a sharp feature at $K=k_0=100$ and have sinusoidal running; the blue/dark spectra correspond to two massive fields ($m_\sigma= 25,60$) excited by this sharp feature and have resonant running.