BICEP's acceleration

TL;DR

The paper explores how BICEP2's detection of primordial B-modes, combined with Planck data, constrains the inflationary acceleration history, potential shape, and reveals features in the primordial power spectrum.

Contribution

It introduces a Monte Carlo method to derive posterior distributions of inflationary acceleration profiles and the primordial power spectrum from current CMB data.

Findings

Significant feature in the scalar primordial spectrum at $k\sim 10^{-3}$ Mpc$^{-1}$

Consistent with previous detection of scalar power suppression

Provides constraints on the inflaton potential shape

Abstract

The recent BICEP2 detection of, what is claimed to be primordial $B$-modes, opens up the possibility of constraining not only the energy scale of inflation but also the detailed acceleration history that occurred during inflation. In turn this can be used to determine the shape of the inflaton potential $V(\phi)$ for the first time - if a single, scalar inflaton is assumed to be driving the acceleration. We carry out a Monte Carlo exploration of inflationary trajectories given the current data. Using this method we obtain a posterior distribution of possible acceleration profiles $\epsilon(N)$ as a function of $e$-fold $N$ and derived posterior distributions of the primordial power spectrum $P(k)$ and potential $V(\phi)$. We find that the BICEP2 result, in combination with Planck measurements of total intensity Cosmic Microwave Background (CMB) anisotropies, induces a significant feature in the scalar primordial spectrum at scales $k\sim 10^{-3}$ Mpc$^{-1}$. This is in agreement with a previous detection of a suppression in the scalar power.