Smoking guns of a bounce in modified theories of gravity through the spectrum of the gravitational waves

Abstract

We present an inflationary model preceded by a bounce in a metric theory a lá $f(R)$ where $R$ is the scalar curvature of the space-time. The model is asymptotically de Sitter such that the gravitational action tends asymptotically to a Hilbert-Einstein action, therefore modified gravity affects only the early stages of the universe. We then analyse the spectrum of the gravitational waves through the method of the Bogoliubov coefficients by two means: taking into account the gravitational perturbations due to the modified gravitational action in the $f(R)$ setup and by simply considering those perturbations inherent to the standard Hilbert-Einstein action. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e. corresponding to modes that are currently entering the horizon.

13 pages, 7 figures. Extensively expanded version. References added. Version accepted in PRD

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• Bounce universe from string-inspired Gauss-Bonnet gravity
• Bouncing cosmology from warped extra dimensional scenario
• Cyclic cosmology in modified gravity
• The interacting multiverse and its effect on the cosmic microwave background
• Scalar perturbations in the late Universe: viability of the Chaplygin gas models
• Interacting Quintessence in a New Scalar-Torsion Gravity
• $f(\mathcal{G},\text{T})$ Gravity Bouncing Universe with Cosmological Parameters
• Chaplygin Gas Hořava-Lifshitz Quantum Cosmology
• Pre-inflation from the multiverse: Can it solve the quadrupole problem in the cosmic microwave background?
• The energy spectrum of gravitational waves in a loop quantum cosmological model
• Gravitational waves from two scalar fields unifying the dark sector with inflation
• A model-independent compact dynamical system formulation for exploring bounce and cyclic cosmological evolutions in $f(R)$ gravity
• Gravitational waves from warm inflation in the weak dissipative regime