A minimal set of invariants as a systematic approach to higher order gravity models: Physical and Cosmological Constraints

TL;DR

This paper systematically evaluates higher order gravity models based on minimal curvature invariants against cosmological observations, identifying models that fit data well but exhibit superluminal mode propagation issues.

Contribution

It introduces a systematic approach using minimal invariants for higher order gravity models and assesses their physical and observational viability.

Findings

Models fit supernova, CMB, and BAO data closely to LCDM.

Some models exhibit superluminal mode propagation.

Physical viability constraints limit the parameter space.

Abstract

We compare higher order gravity models to observational constraints from magnitude-redshift supernova data, distance to the last scattering surface of the CMB, and Baryon Acoustic Oscillations. We follow a recently proposed systematic approach to higher order gravity models based on minimal sets of curvature invariants, and select models that pass some physical acceptability conditions (free of ghost instabilities, real and positive propagation speeds, and free of separatrices). Models that satisfy these physical and observational constraints are found in this analysis and do provide fits to the data that are very close to those of the LCDM concordance model. However, we find that the limitation of the models considered here comes from the presence of superluminal mode propagations for the constrained parameter space of the models.