The refractive index of relic gravitons

Abstract

The dynamical evolution of the refractive index of the tensor modes of the geometry produces a specific class of power spectra characterized by a blue (i.e. slightly increasing) slope which is directly determined by the competition of the slow-roll parameter and of the rate of variation of the refractive index. Throughout the conventional stages of the inflationary and post-inflationary evolution, the microwave background anisotropies measurements, the pulsar timing limits and the big-bang nucleosythesis constraints set stringent bounds on the refractive index and on its rate of variation. Within the physically allowed region of the parameter space the cosmic background of relic gravitons leads to a potentially large signal for the ground based detectors (in their advanced version) and for the proposed space-borne interferometers. Conversely, the lack of direct detection of the signal will set a qualitatively new bound on the dynamical variation of the refractive index.

30 pages, 7 figures

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Cited by in corpus (20)

• Primordial backgrounds of relic gravitons
• Cosmological constraints on slow-roll inflation: an update
• Intermittent null energy condition violations during inflation and primordial gravitational waves
• Propagating Speed of Primordial Gravitational Waves
• Propagating speed of primordial gravitational waves and inflation
• Inflation, the Hubble Tension and Early Dark Energy: an alternative overview
• Towards a reliable calculation of relic radiation from primordial gravitational waves
• Inflationary Potential as seen from Different Angles: Model Compatibility from Multiple CMB Missions
• Higher-Curvature Corrections and Tensor Modes
• Primordial tensor non-Gaussianities from general single-field inflation with non-Bunch-Davies initial states
• Tracking the Multifield Dynamics with Cosmological Data: A Monte Carlo approach
• Post-inflationary thermal histories and the refractive index of relic gravitons
• Glauber theory and the quantum coherence of curvature inhomogeneities
• The propagating speed of relic gravitational waves and their refractive index during inflation
• Modified gravity as a diagravitational medium
• Quantum coherence of relic gravitons and Hanbury Brown-Twiss interferometry
• The refractive index of the relic gravitons and the nHz band
• Relic gravitons and pulsar timing arrays: a theoretical viewpoint
• Flat spectra of cosmic gravitons in the nHz and audio bands
• Relic gravitons at intermediate frequencies and the expansion history of the Universe