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

Abstract

The problem of cosmological production of gravitational waves is discussed in the framework of an expanding, spatially homogeneous and isotropic FRW type Universe with time-evolving vacuum energy density. The gravitational wave equation is established and its modified time-dependent part is analytically resolved for different epochs in the case of a flat geometry. Unlike the standard ΛCDM cosmology (no interacting vacuum), we show that gravitational waves are produced in the radiation era even in the context of general relativity. We also show that for all values of the free parameter, the high frequency modes are damped out even faster than in the standard cosmology both in the radiation and matter-vacuum dominated epoch. The formation of the stochastic background of gravitons and the remnant power spectrum generated at different cosmological eras are also explicitly evaluated. It is argued that measurements of the CMB polarization (B-modes) and its comparison with the rigid ΛCDM model plus the inflationary paradigm may become a crucial test for dynamical dark energy models in the near future.PACS number: 04.30.Db, 95.36.+x,

Running vacuum cosmological models: linear scalar perturbations

“…been studied in detail in [25,42,51,52]. Whereas, the high order terms, which produce the inflationary stage, were studied by [53][54][55] among others.…”

Constraints on a special running vacuum model

“…In this kind of the models, Λ, instead of being a constant, is a function of the Hubble parameter H, and decays to matter and radiation [8]. It has been shown that the RVMs are suitable in describing the cosmological evolutions on both background and linear perturbation levels in the literature [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. In these studies, the Hubble parameter H has been used to compose many forms of Λ =…”

Constraints on running vacuum model withH(z) andfσ8

“…In this model, the cosmological constant Λ is described by a function of the Hubble parameter and decays to matter and radiation in the expansion of the universe [8]. It has been shown that the RVM is suitable in describing the cosmological evolution on both background and linear perturbation levels [21][22][23][24][25][26][27][28][29][30].…”