Primordial gravitational waves in running vacuum cosmologies

Abstract

We investigate the cosmological production of gravitational waves in a nonsingular flat cosmology powered by a "running vacuum" energy density described by ρ Λ ≡ ρ Λ (H), a phenomenological expression potentially linked with the renormalization group approach in quantum field theory in curved spacetimes. The model can be interpreted as a particular case of the class recently discussed by Perico et al. (Phys. Rev. D 88, 063531, 2013) which is termed complete in the sense that the cosmic evolution occurs between two extreme de Sitter stages (early and late time de Sitter phases). The gravitational wave equation is derived and its time-dependent part numerically integrated since the primordial de Sitter stage. The generated spectrum of gravitons is also compared with the standard calculations where an abrupt transition, from the early de Sitter to the radiation phase, is usually assumed. It is found that the stochastic background of gravitons is very similar to the one predicted by the cosmic concordance model plus inflation except at higher frequencies (ν 100 kHz). This remarkable signature of a "running vacuum" cosmology combined with the proposed high frequency gravitational wave detectors and measurements of the CMB polarization (Bmodes) may provide a new window to confront more conventional models of inflation.

Production of primordial gravitational waves in a simple class of running vacuum cosmologies

“…This is one of the main aims of the present paper. Recent similar studies have appear in the literature Similar recent studies have appeared in the literature [35].…”

Gravitational Waves in Decaying Vacuum Cosmologies

“…Using the Einstein equations and the above solutions we can obtain the corresponding energy densities: 34) withρ I ≡ 3H 2 I /8πG. These expressions reproduce the energy densities for the primeval de Sitter and radiation dominated epochs, for details see Figure 5.1.…”

“…It is found that the spectrum is very similar to the one predicted by the cosmic concordance model plus inflation except for high frequencies. The first results of this part have been submitted for publication [34].…”

“…The model can be interpreted as a particular case of the large class of cosmologies which is termed complete in the sense that the cosmic evolution occurs between two extreme de Sitter stages (early and late time de Sitter phases). The first results obtained were published in [34].…”

Modern theoretical cosmological models and their observational predictions

“…• the effects of expansion on the GW group and phase velocities [409,410] • mathematical aspects and exact solutions [411][412][413][414][415] • quantum and thermodynamic properties of GWs [124,416] • general properties [414,417,418] • nonlinear effects [419] • properties of the GW energy momentum tensor [420] • collision of GWs with electromagnetic waves [421] • evolution of GWs in gravitational plasma [422] Even though these studies have properly taken into account the expansion of the background metric, they have not taken into account the effects of the gravitational field of mass distributions on the evolution of the GWs. Such a gravitational field combined with the expanding background may induce new observable effects on the spectrum of propagating gravitational waves affecting the amplitude and the frequency of such waves, due to gravitational time delay [423].…”