We consider a simple model of modified gravity interacting with a single scalar field φ with weakly coupled exponential potential within the framework of non-Riemannian spacetime volume-form formalism. The specific form of the action is fixed by the requirement of invariance under global Weyl-scale symmetry. Upon passing to the physical Einstein frame we show how the non-Riemannian volume elements create a second canonical scalar field u and dynamically generate a non-trivial two-scalar-field potential Ueff (u , φ) with two remarkable features: (i) it possesses a large flat region for large u describing a slow-roll inflation; (ii) it has a stable low-lying minimum w.r.t. (u , φ) representing the dark energy density in the "late universe". We study the corresponding two-field slow-roll inflation and show that the pertinent slow-roll inflationary curve φ = φ (u) in the two-field space (u , φ) has a very small curvature, i.e., φ changes very little during the inflationary evolution of u on the flat region of Ueff (u , φ). Explicit expressions are found for the slow-roll parameters which differ from those in the single-field inflationary counterpart. Numerical solutions for the scalar spectral index and the tensor-to-scalar ratio are derived agreeing with the observational data.
Nuclear Physics B
- Pub Date:
- February 2020
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- General Relativity and Quantum Cosmology;
- High Energy Physics - Theory
- 13 pages. 2 Fig. arXiv admin note: text overlap with arXiv:1906.06691 , v.2 14 pages, typos corrected, additional explanations