Density perturbations in nonminimally coupled gravity: symptoms of Lagrangian density ambiguity

2025/05/15 by Varela, Miguel Barroso, Bertolami, Orfeu · 3 citations
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc)

paper · doi:10.48550/arxiv.2505.10291

Abstract

The evolution of density perturbations is analysed in a modified theory of gravity with a nonminimal coupling between curvature and matter. We consider the broken degeneracy between the choices of matter Lagrangian for a perfect fluid, L_m=-ρ and L_m=p, and determine the differences between their effects on the effective gravitational constant. We review the result for L_m=-ρ in the quasistatic approximation and show how it can lead to unphysical singular behaviour for late-time dominating models. This divergent regime can be avoided when considering the fully non-quasistatic perturbative equations, although the higher-order nature of the nonminimally coupled theory and the requirement of a physically viable effective gravitational constant strongly constrains the magnitude of these modifications to the action. We find that both of these issues can be removed when considering L_m=p at late times due to the pressureless nature of non-relativistic matter and provide predictions for inverse power-law models.

Citations

• Consistent energy-momentum trace couplings of fluids
• DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints
• Investigating Late-Time Dark Energy and Massive Neutrinos in Light of DESI Y1 BAO
• DESI 2024 VI: cosmological constraints from the measurements of baryon acoustic oscillations
• Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies
• The Pantheon+ Analysis: Cosmological Constraints
• Planck 2018 results
• Homogeneous spherically symmetric bodies with a nonminimal coupling between curvature and matter: the choice of the Lagrangian density for matter
• Modern Cosmology
• Stability of a cosmological model with dynamical cancellation of vacuum energy
• Realistic cosmological model with dynamical cancellation of vacuum energy
• Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
• Action functionals for relativistic perfect fluids
• Perfect Fluids in General Relativity: Velocity Potentials and a Variational Principle

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