Precision calculations of the gravitational wave background spectrum from inflation

Abstract

The spectrum of the gravitational wave background originating from quantum fluctuations during inflation is calculated numerically for various inflation models over a wide range of frequencies. We take into account four ingredients : the scalar field dynamics during inflation making no use of the slow-roll approximation, the fermionic decay of the scalar field with a small coupling constant during the reheating process, the change of the effective number of degrees of freedom g_* in the radiation-dominated era, and the anisotropic stress of free-streaming neutrinos. By numerically solving the evolution of gravitational waves during and after inflation up to the present, all of these effects can be examined comprehensively and accurately over a broad spectrum, even at very high frequencies. We find that the spectrum shows (i) a large deviation from the spectrum less accurate obtained by Taylor expanding around the CMB scale using the slow-roll approximation (ii) a characteristic frequency dependence due to the reheating effect, and (iii) damping due to the g_* changes and the neutrino anisotropic stress. We suggest that future analysis of the gravitational wave background should take into consideration the fact that analytical estimates using the Taylor expansion overestimate the amplitude of the spectrum.

15 pages, 7 figures, accepted for publication in PRD, This version contains major revisions over the previous version, with added calculations of neutrino anisotropic stress; typos corrected

References in corpus (11)

• Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations
• Theory and Numerics of Gravitational Waves from Preheating after Inflation
• A Gravitational Wave Background from Reheating after Hybrid Inflation
• A stochastic background of gravitational waves from hybrid preheating
• Probing reheating temperature of the universe with gravitational wave background
• Search for a stochastic background of 100-MHz gravitational waves with laser interferometers
• Laser-interferometric Detectors for Gravitational Wave Background at 100 MHz : Detector Design and Sensitivity
• The inflationary gravitational-wave background and measurements of the scalar spectral index
• Stochastic gravitational wave background from cold dark matter halos
• Effective Search Templates for a Primordial Stochastic Gravitational Wave Background
• Optimal Location of Two Laser-interferometric Detectors for Gravitational Wave Backgrounds at 100 MHz