The MESS of the CMB

TL;DR

This paper introduces the MESS framework to analyze CMB data, accounting for primordial entropy effects, leading to improved fits and offering a model-independent way to study early universe perturbations.

Contribution

It presents a minimal modification to existing CMB analysis codes to incorporate a momentum-dependent effective sound speed, enabling a model-independent study of primordial entropy effects.

Findings

Improved fit to CMB data with MESS compared to models without it.

Primordial entropy modeled by MESS can explain deviations from scale invariance.

Method is compatible with existing numerical codes for CMB analysis.

Abstract

We analyze cosmic microwave background (CMB) data taking into account the effects of a momentum dependent effective sound speed (MESS). This approach allows to study the effects of primordial entropy in a model independent way, and its implementation requires a minimal modification of existing CMB fitting numerical codes developed for single scalar field models. We adopt a phenomenological approach, and study the effects a local variation of the MESS around the scale where other analysis have shown some deviation from an approximately scale invariant curvature perturbation spectrum. We obtain a substantial improvement of the fit with respect to a model without MESS, showing that primordial entropy modeled by MESS can be an explanation of these deviations.