Massive Fields as Systematics for Single Field Inflation

TL;DR

Massive fields during inflation can significantly bias the inflationary parameter estimates, especially when their mass is comparable to the Hubble scale, posing challenges for precise inflation model selection.

Contribution

This paper analyzes how massive fields influence inflationary observables and highlights their potential to cause significant shifts in the $n_s$-$r$ diagram, affecting model discrimination.

Findings

Massive fields with mass ~ H can bias inflationary parameters.

Significant shifts occur when massive fields have mass ~ 70H.

Systematics from massive fields challenge future precision in inflation studies.

Abstract

During inflation, massive fields can contribute to the power spectrum of curvature perturbation via a dimension-5 operator. This contribution can be considered as a bias for the program of using $n_s$ and $r$ to select inflation models. Even the dimension-5 operator is suppressed by $\Lambda = M_p$, there is still a significant shift on the $n_s$-$r$ diagram if the massive fields have $m\sim H$. On the other hand, if the heavy degree of freedom appears only at the same energy scale as the suppression scale of the dimension-5 operator, then significant shift on the $n_s$-$r$ diagram takes place at $m=\Lambda \sim 70H$, which is around the inflationary time-translation symmetry breaking scale. Hence, the systematics from massive fields pose a greater challenge for future high precision experiments for inflationary model selection. This result can be thought of as the impact of UV sensitivity to inflationary observables.