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We demonstrate that any scaling source in the radiation era produces a background of gravitational waves with an exact scale-invariant power spectrum. Cosmic defects, created after a phase transition in the early universe, are such a scaling source. We emphasize that the result is independent of the topology of the cosmic defects, the order of phase transition, and the nature of the symmetry broken, global or gauged. As an example, using large-scale numerical simulations, we calculate the scale-invariant gravitational wave power spectrum generated by the dynamics of a global O(N) scalar theory. The result approaches the large N theoretical prediction as N-2, albeit with a large coefficient. The signal from global cosmic strings is 0(100) times larger than the large N prediction. [ABSTRACT FROM AUTHOR]

We study the energy distribution and equation of state of the universe between the end of inflation and the onset of radiation domination (RD), considering observationally consistent single-field inflationary scenarios, with a potential 'flattening' at large field values, and a monomial shape V (ϕ) ∝ | ϕ | p around the origin. As a proxy for (p)reheating, we include a quadratic interaction g 2 ϕ 2 X 2 between the inflaton ϕ and a light scalar 'daughter' field X , with g 2 > 0. We capture the non-perturbative and non-linear nature of the system dynamics with lattice simulations, obtaining that: i) the final energy transferred to X depends only on p , not on g 2 ; i i) the final transfer of energy is always negligible for 2 ≤ p < 4 , and of order ∼ 50 % for p ≥ 4 ; i i i) the system goes at late times to matter-domination for p = 2 , and always to RD for p > 2. In the latter case we calculate the number of e-folds until RD, significantly reducing the uncertainty in the inflationary observables n s and r. [ABSTRACT FROM AUTHOR]