Understanding large scale CMB anomalies with the generalized non-minimal derivative coupling during inflation

TL;DR

This paper investigates how a generalized non-minimal derivative coupling during inflation can explain large-scale anomalies in the CMB, proposing specific models that improve fit over standard cosmology and discussing future observational constraints.

Contribution

It introduces a model-independent framework for GNMDC during inflation and demonstrates its potential to account for CMB anomalies with improved fit over the standard model.

Findings

Hilltop-quartic model with GNMDC improves fit to CMB data

Future CMB experiments will further constrain GNMDC parameters

Model-independent constraints on GNMDC functions derived

Abstract

We study the observational implications of a class of inflationary models wherein the inflaton is coupled to the Einstein tensor through a generalized non-minimal derivative coupling (GNMDC). In particular, we explore whether these models can generate suitable features in the primordial spectrum of curvature perturbations as a possible explanation for the large-scale anomalies associated with the angular power spectrum of CMB temperature anisotropies. We derive model-independent constraints on the GNMDC function for such a scenario, considering both the scalar and tensor perturbations. We modify CosmoMC to accommodate our GNMDC framework and investigate different classes of inflationary models using a fully consistent numerical approach. We find that the hilltop-quartic model with a specific choice of the GNMDC function provides a considerable improvement over the best-fit reference $\Lambda$CDM model with a nearly scale-invariant power spectrum. While the large-scale structure observations should be able to provide independent constraints, future CMB experiments, such as CMB-S4 and CMB-Bharat, are expected to constrain further the parameter space of such beyond canonical single-field inflationary models.