Theory space and stability analysis of General Relativistic cosmological solutions in modified gravity
Year: 2026
Type: article
Abstract: Some aspects of two General Relativistic cosmological solutions, an exact $$\Lambda $$ Λ CDM-like cosmological solution $$j=1$$ j = 1 ( j is cosmographic jerk parameter), and a specifically designed toy cosmological solution $$j=1+3\varepsilon (q-1/2)$$ j = 1 + 3 ε ( q - 1 / 2 ) ( q is cosmographic deceleration parameter, $$0<|\varepsilon |<1$$ 0 < | ε | < 1 ) that is capable of accommodating a phantom crossing scenario as suggested by DESI DR2, are studied within the context of f ( R ) gravity, by portraying them as a flow in the 2-dimensional theory space spanned by the quantities $$r=\frac{R f'}{f}, m=\frac{R f''}{f'}$$ r = R f ′ f , m = R f ′ ′ f ′ . For the f ( R ) theories exactly reproducing a background $$\Lambda $$ Λ CDM-like expansion history $$j=1$$ j = 1 , it is shown by means of a cosmographic reconstruction approach that the curvature degree of freedom need not necessarily behave like an effective cosmological constant, and that cosmologies under different possible such theories lead to different possible values of $$\Omega _{m0}$$ Ω m 0 . With the theory space analysis, it is also shown that $$\Lambda $$ Λ CDM-mimicking f ( R ) cosmologies that asymptote to General Relativistic $$\Lambda $$ Λ CDM in the limit $$q\rightarrow 1/2$$ q → 1 / 2 , are prone to instability under small homogeneous and isotropic perturbation, casting a doubt on achieving an exact
Source: The European Physical Journal C
Authors: Saikat Chakraborty, Piyabut Burikham
Institution: Chulalongkorn University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Awards: G6460652345, G654486882
OpenAlex ID: W7138134703