Primordial perturbations with pre-inflationary bounce

TL;DR

This paper develops a stable bounce inflation model using EFT, showing it can explain large-scale suppression and a dip in the CMB spectrum, with results sensitive to bounce physics.

Contribution

It introduces a ghost-free, stable bounce inflation model with detailed perturbation evolution, explaining CMB anomalies better than previous models.

Findings

Large-scale suppression in perturbation spectrum

Better fit to CMB dip at multipole l~20

Valley depth depends on bounce physics

Abstract

Based on the effective field theory (EFT) of nonsingular cosmologies, we build a stable model, without the ghost and gradient instabilities, of bounce inflation (inflation is preceded by a cosmological bounce). We perform a full simulation for the evolution of scalar perturbation, and find that the perturbation spectrum has a large-scale suppression (as expected), which is consistent with the power deficit of the cosmic microwave background (CMB) TT-spectrum at low multipoles, but unexpectedly, it also shows itself one marked lower valley, which actually provides a better fit to the dip at multipole $l\sim 20$. The depth of valley is relevant with the physics around the bounce scale, which is model-dependent.