Optimizing future experimental probes of inflation

TL;DR

This paper investigates the degeneracy problem in inflationary models, showing that future measurements of isocurvature modes or tensor spectral index are crucial for accurately reconstructing the inflationary potential.

Contribution

It demonstrates the limitations of future observational probes in resolving degeneracies in inflation models, emphasizing the importance of specific observables for potential reconstruction.

Findings

Degeneracy remains high without additional observables.

Future measurements of isocurvature modes improve potential reconstruction.

Tensor spectral index measurements significantly aid in breaking degeneracies.

Abstract

The discovery of many novel realizations of the inflationary universe paradigm has led to a degeneracy problem: many different inflationary Lagrangians generate the same perturbation spectra. Resolving this problem requires the future discovery of additional observables, beyond the scalar adiabatic and tensor two-point functions on CMB scales. One important source of degeneracy arises in models where the density perturbation is generated by a non-inflationary degree of freedom, for example, through curvatons or modulated reheating. We consider the curvaton scenario as representative of this class, and analyze the degeneracy with single field, canonical inflation that results if the curvaton goes undetected by future observations. We perform Monte Carlo potential reconstructions in the absence of distinguishing observables, such as non-Gaussiantities or isocurvature modes. The resulting degeneracy is considerable and the improved measurements of spectral parameters from future probes like CMBPol, offer little to better the situation. Given a degeneracy-breaking observation, the observables must still be inverted to obtain the inflationary potential, with different observations resulting in reconstructions of varying quality. We find that a future detection of isocurvature modes or a precision measurement of the tensor spectral index will enable the most successful reconstructions in the presence of curvatons.