How to constrain inflationary parameter space with minimal priors

TL;DR

This paper compares analytical and numerical methods for constraining inflationary parameters using CMB and LSS data, highlighting the importance of priors and recommending exact numerical approaches for accuracy.

Contribution

It systematically evaluates the impact of priors and approximation methods on inflationary parameter constraints, emphasizing the need for exact numerical calculations.

Findings

Priors can alter bounds on inflationary parameters by up to a factor of two.

Analytical approximations are sufficiently accurate within the minimal prior region.

Exact numerical methods are recommended for self-consistent cosmological data analysis.

Abstract

We update constraints on the Hubble function H(phi) during inflation, using the most recent cosmic microwave background (CMB) and large scale structure (LSS) data. Our main focus is on a comparison between various commonly used methods of calculating the primordial power spectrum via analytical approximations and the results obtained by integrating the exact equations numerically. In each case, we impose naive, minimally restrictive priors on the duration of inflation. We find that the choice of priors has an impact on the results: the bounds on inflationary parameters can vary by up to a factor two. Nevertheless, it should be noted that within the region allowed by the minimal prior of the exact method, the accuracy of the approximations is sufficient for current data. We caution however that a careless minimal implementation of the approximative methods allows models for which the assumptions behind the analytical approximations fail, and recommend using the exact numerical method for a self-consistent analysis of cosmological data.