Platonic solids back in the sky: Icosahedral inflation

TL;DR

This paper extends solid inflation models to include anisotropic cosmic solids with icosahedral symmetry, predicting highly anisotropic higher-point correlations and tensor functions, impacting CMB data analysis.

Contribution

It identifies icosahedral symmetry as the unique anisotropic solid inflation model consistent with observed isotropy, and explores the resulting anisotropic correlation functions.

Findings

Higher-point functions are maximally anisotropic.

Tensor two-point function can be highly anisotropic with higher-derivative couplings.

Standard detection strategies may be inefficient for these anisotropic signals.

Abstract

We generalize the model of solid inflation to an anisotropic cosmic solid. Barring fine tunings, the observed isotropy of the cosmological background and of the scalar two-point function isolate the icosahedral group as the only possible symmetry group of such a solid. In such a case, higher-point correlation functions---starting with the three-point one---are naturally maximally anisotropic, which makes the standard detection strategies highly inefficient and calls for a dedicated analysis of CMB data. The tensor two-point function can also be highly anisotropic, but only in the presence of sizable higher-derivative couplings.