Constraining Inflation with Cosmic Microwave Background Polarization

TL;DR

The paper argues that CMB polarization provides tighter, more robust constraints on inflationary parameters than temperature data alone, enabling finer discrimination among single-field slow-roll models. It links inflationary potentials to observable spectra via the slow-roll parameters and employs a Fisher-matrix framework to forecast MAP and Planck capabilities, including reionization effects. The key result is that polarization reduces degeneracies with reionization and can detect very small tensor-to-scalar ratios (down to r ~ 0.01) with modest sensitivity improvements, potentially distinguishing between different small-field potentials. These findings underscore polarization as a crucial tool for precision tests of inflation and motivate enhanced or ground-based experiments to push beyond Planck's capabilities.

Abstract

Observations of the polarization of the cosmic microwave backround (CMB) have the potential to place much tighter constraints on cosmological parameters than observations of the fluctuations in temperature alone. We discuss using CMB polarization to constrain parameters relevant for distinguishing among popular models for cosmological inflation, using the MAP and Planck satellite missions as example cases. Of particular interest is the ability to detect tiny contributions to the CMB anisotropy from tensor modes, which is fundamentally limited by cosmic variance in temperature-only observations. The ability to detect a tensor/scalar ratio $r \sim 0.01$ would allow precision tests of interesting inflation models, and is possible with a modest increase in sensitivity over that planned for the Planck satellite, or potentially by ground-based experiments.

Figures (8)

• Figure 1: Typical temperature/polarization spectra for the fiducial case $n = 0.9$, $r = 0.7$, $\tau_{\rm ri} = 0.05$.
• Figure 2: The parameter space divided into regions for small-field, large-field and hybrid models. The linear case is the dividing line between large- and small-field.
• Figure 3: $2-\sigma$ error ellipses for MAP (no reionization), with $n = 0.9$ and $r = 0.7$. The T only and T+P ellipses overlap almost exactly in this case.
• Figure 4: Error ellipses for Planck (no reionization), with $n = 0.9$ and $r = 0.7$. In this case, polarization results in a noticeable increase in sensitivity.
• Figure 5: Error ellipses for MAP ($\tau_{\rm ri} = 0.05$). With reionization, the T-only error is much larger than for the case with no reionization, but the T+P case is mostly unaffected.