Reconciliation of High Energy Scale Models of Inflation with Planck

TL;DR

This paper investigates how unknown high-scale physics affecting initial conditions of inflation can alter observable predictions, potentially reconciling simple inflation models with Planck data.

Contribution

It demonstrates that certain initial states influenced by high-energy physics can significantly modify inflationary observables, especially tensor-to-scalar ratio, aligning models with observational data.

Findings

Initial states can significantly alter power spectra amplitude.

Modification in bispectrum remains small for these initial states.

High-scale physics can suppress tensor-to-scalar ratio, reconciling models with Planck data.

Abstract

The inflationary cosmology paradigm is very successful in explaining the CMB anisotropy to the percent level. Besides the dependence on the inflationary model, the power spectra, spectral tilt and non-Gaussianity of the CMB temperature fluctuations also depend on the initial state of inflation. Here, we examine to what extent these observables are affected by our ignorance in the initial condition for inflationary perturbations, due to unknown new physics at a high scale $M$. For initial states that satisfy constraints from backreaction, we find that the amplitude of the power spectra could still be significantly altered, while the modification in bispectrum remains small. For such initial states, $M$ has an upper bound of a few tens of $H$, with $H$ being the Hubble parameter during inflation. We show that for $M\sim 20 H$, such initial states always (substantially) suppress the tensor to scalar ratio. In particular we show that a general choice of initial conditions can satisfactorily reconcile the simple $1/2 m^2 \phi^2$ chaotic model with the Planck data.