Late-time reconstruction of non-minimally coupled gravity with a smoothness prior

TL;DR

This paper develops a non-parametric, model-independent method to reconstruct non-minimally coupled gravity effects from cosmological data, revealing hints of non-minimal coupling and phantom crossing in dark energy.

Contribution

It introduces a smoothness prior for stable, model-agnostic reconstruction of non-minimal gravity functions from diverse cosmological observations.

Findings

2.8σ hint for non-minimal coupling from data

Preference for dark energy equation of state crossing -1

Non-minimal coupling stabilizes dark energy perturbations

Abstract

We present a non-parametric, model-independent reconstruction of the cosmological background and perturbation dynamics in non-minimally coupled theories of gravity. Within the Effective Field Theory of dark energy framework, we reconstruct the time-dependent cosmological constant, $\Lambda(t)$, and the non-minimal coupling function, $\Omega(t)$, from cosmological data. To ensure stability, we apply a correlated smoothness prior that restricts the reconstruction to the space of sufficiently smooth functions. Using CMB, DESI BAO, Type Ia supernovae, CMB-ISW lensing cross-correlations, and large-scale 3x2pt DES Year 3 data, we find a $2.8\sigma$ hint for a non-minimal coupling. For the dark energy equation of state, our results indicate a preference for the existence of crossing of the phantom divide, $w_{DE}=-1$, at $z<0.8$. The non-minimal coupling effect stabilizes dark energy perturbations, providing a viable physical interpretation of the phantom crossing scenario. Our work paves the way for model-agnostic searches for signatures of modified gravity in cosmological data.