Towards model agnostic F(R) gravity inflation
Oikonomou V.K.
October 2025Institute of Physics
Journal of Cosmology and Astroparticle Physics
2025#2025Issue 10
In this work we construct a formalism that can reveal the general characteristics of classes of viable F(R) inflationary theories. The assumptions we make is that the slow-roll era occurs, and that the de Sitter scalaron mass m2(R) of the F(R) gravity is positive or zero, for both the inflationary and late-time quasi de Sitter eras, a necessary condition for the stability of the de Sitter spacetime. In addition, we require that the de Sitter scalaron mass is also a monotonically increasing function of the Ricci scalar, or it has an extremum. Also the F(R) gravity function is required to depend on the two known fundamental scales in cosmology, the cosmological constant Λ and the mass scale m2s = κ2ρ3(0) m , with ρ(0)m denoting the energy density of the cold dark matter at the present epoch, that is F(R) = F(R,Λ,m2s). Using these general assumptions we provide the general features of viable classes of F(R) gravity inflationary theories which remarkably can also simultaneously describe successfully the dark energy era. This unique feature of a unified description of the dark energy and inflationary eras stems from the requirement of the monotonicity of the de Sitter scalaron mass m2(R). These viable classes are either deformations of the R2 model or α-attractors type theories. The analysis of the viability of a general F(R) gravity inflationary theory is reduced in evaluating the parameter x = RFFRRRRR and the first slow-roll index of the theory, either numerically or approximately. We also disentangle the power-law F(R) gravities from power-law evolution and we show that power-law F(R) gravities can be viable theories of inflation, for appropriate values of the power-law exponent. Finally we highlight the phenomenological importance of exponential deformations of the R2 model of the form F(R) = R+ MR22 + λReϵ(R Λ)β + λΛnϵ, which emerge naturally as viable inflationary models which also describe successfully the dark energy era.
dark energy theory , inflation , modified gravity
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Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
L.N. Gumilyov Eurasian National University, Astana, 010008, Kazakhstan
Department of Physics
L.N. Gumilyov Eurasian National University
10 лет помогаем публиковать статьи Международный издатель
Книга Публикация научной статьи Волощук 2026 Book Publication of a scientific article 2026