Forecast Constraints on Inflation from Combined CMB and Gravitational Wave Direct Detection Experiments

TL;DR

Combining CMB polarization data with direct gravitational wave detection experiments like BBO can significantly improve constraints on inflationary parameters, breaking degeneracies and enhancing our understanding of inflation models.

Contribution

This paper demonstrates how direct detection experiments complement CMB measurements to better constrain inflationary parameters and break degeneracies.

Findings

BBO improves tensor-to-scalar ratio constraints over Planck alone.

Combining BBO with CMB data reduces parameter degeneracies.

Addition of BBO enhances constraints even for cosmic variance-limited CMB experiments.

Abstract

We study how direct detection of the inflationary gravitational wave background constrains inflationary parameters and complements CMB polarization measurements. The error ellipsoids calculated using the Fisher information matrix approach with Planck and the direct detection experiment, BBO (Big Bang Observer), show different directions of parameter degeneracy, and the degeneracy is broken when they are combined. For a slow-roll parameterization, we show that BBO could significantly improve the constraints on the tensor-to-scalar ratio compared with Planck alone. We also look at a quadratic and a natural inflation model. In both cases, if the temperature of reheating is also treated as a free parameter, then the addition of BBO can significantly improve the error bars. In the case of natural inflation, we find that the addition of BBO could even partially improve the error bars of a cosmic variance-limited CMB experiment.