N. Frusciante, S. Peirone

Abstract
The Effective Field Theory (EFT) framework for dark energy (DE) provides an effective description for cosmological perturbations of genuine departures from General Relativity (GR). It encompasses any dark energy and modified gravity (MG) models with one additional scalar degree of freedom (DoF) through a variety of geometrical operators compatible with the residual symmetries of unbroken spatial diffeomorphisms. The operators are organised in powers of the number of perturbations and spatial derivatives, and each of them multiplies a time-dependent function, called EFT function.

Hybrid Metric-Palatini Gravity and Cosmology. An Update by the CANTATA Network.
Emmanuel N. Saridakis, Ruth Lazkoz, Vincenzo Salzano, Paulo Vargas Moniz, Salvatore Capozziello, Jose Beltrán Jiménez, Mariafelicia De Laurentis, Gonzalo J. Olmo

Springer Nature, Page 465
2021 December

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