- The paper introduces modified f(R) and F(G) gravity models that unify early inflation with the current ΛCDM epoch while addressing instability challenges.
- It employs tuning of the effective cosmological constant to bridge high-energy inflation and low-energy cosmic acceleration consistent with observations.
- The models successfully mitigate classical instabilities and deviations from Newton’s law, paving the way for experimental validation in cosmology.
Unifying Inflation and LambdaCDM Epoch through Modified f(R) Gravity
The paper under examination posits a significant exploration into the field of modified f(R) gravity, proposing innovative models that aim to coherently describe both early-time inflation and late-time acceleration of the universe. The primary objective is to present versions of these theories capable of passing local gravitational tests, such as those in the Solar System, while remaining consistent with broader cosmological observations.
Overview and Motivation
The paper intricately crafts two models of f(R) gravity and an F(G) gravity model, aiming for a unified explanation encompassing the vast dynamical range from inflation to the current accelerating expansion. Modified gravity, rooted in broader theories like string/M-theory, presents a compelling avenue for addressing the enigma of dark energy without invoking exotic forms of matter. Given the complexities associated with traditional f(R) constructions, these models also address the prevailing challenges, such as classical instabilities and deviations from Newton's law at cosmological scales, ensuring that they maintain coherence with accepted physical laws and astronomical data.
- Modified f(R) Model: The first proposed framework modifies existing formulations to naturally integrate early universe inflation with the late-time cosmic acceleration adhering to the ΛCDM model. The key feature here is its resilience against classical instabilities and adherence to Solar System tests, albeit with potential anti-gravity scenario development, necessitating adjustments to circumvent this issue.
- Viable F(G) Gravity: The authors extend their investigation to F(G) gravity, leveraging the Gauss-Bonnet invariant. This model effectively avoids problems like violations of the Newtonian limit and introduces no instabilities or anti-gravity regimes, a notable advancement over previous attempts.
Notable Results
Noteworthy is the achievement of the models to reproduce the characteristic features of the ΛCDM model while mitigating known limitations of earlier f(R) models, such as matter instability and large-scale deviations of gravitational properties. Particularly, the expressions are carefully tuned for the effective cosmological constant to evolve from high values in the early universe, facilitating inflation, to the current observed small values, enabling late-time acceleration. Quantitative predictions, such as the absence of significant deviations in the Newtonian gravitational force, underscore the viability of the approaches within current parameter constraints.
Implications and Future Directions
These proposals bear theoretical significance as they bridge two critical cosmological epochs under a singular, mathematically consistent framework without the need for dark energy constituents. Practically, they provoke further research into the subtle variations of modulated gravity theories, opening avenues for experimental verification as future precision gravitational and cosmological observations become available.
Further explorations could refine these models to accommodate observational advancements and address the subtleties of cosmic structure formation and the precise dynamics of scalar perturbations. Ultimately, these developments could potentiate a paradigm shift in understanding gravitational interactions on cosmological scales. The ongoing quest will be to generalize these models to ensure robustness across broader conditions and observational datasets, providing a stepping stone towards a comprehensive gravitational theory.