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Abstract: The spectrum of the gravitational wave background originating from quantumfluctuations during inflation is calculated numerically for various inflationmodels over a wide range of frequencies. We take into account four ingredients: the scalar field dynamics during inflation making no use of the slow-rollapproximation, the fermionic decay of the scalar field with a small couplingconstant during the reheating process, the change of the effective number ofdegrees of freedom g * in the radiation-dominated era, and the anisotropicstress of free-streaming neutrinos. By numerically solving the evolution ofgravitational waves during and after inflation up to the present, all of theseeffects can be examined comprehensively and accurately over a broad spectrum,even at very high frequencies. We find that the spectrum shows i a largedeviation from the spectrum less accurate obtained by Taylor expanding aroundthe CMB scale using the slow-roll approximation ii a characteristic frequencydependence due to the reheating effect, and iii damping due to the g *changes and the neutrino anisotropic stress. We suggest that future analysis ofthe gravitational wave background should take into consideration the fact thatanalytical estimates using the Taylor expansion overestimate the amplitude ofthe spectrum.



Author: Sachiko Kuroyanagi, Takeshi Chiba, Naoshi Sugiyama

Source: https://arxiv.org/







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