Primordial Gravitational Waves in Running Vacuum Cosmologies

TL;DR

This paper explores how a running vacuum energy model in cosmology influences primordial gravitational wave production, revealing distinctive high-frequency signatures that could be detected with future gravitational wave experiments and CMB polarization measurements.

Contribution

It introduces a detailed analysis of gravitational wave spectra in a running vacuum cosmology, highlighting differences from standard models at high frequencies and suggesting observational tests.

Findings

Gravitational wave spectrum similar to standard models at low frequencies

Distinct high-frequency signatures above 100 kHz

Potential for new observational tests with future detectors

Abstract

We investigate the cosmological production of gravitational waves in a nonsingular flat cosmology powered by a "running vacuum" energy density described by $\rho_{\Lambda}\equiv\rho_{\Lambda}(H)$, 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 {\bf 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 ($\nu \gtrsim 100$ kHz). This remarkable signature of a "running vacuum" cosmology combined with the proposed high frequency gravitational wave detectors and measurements of the CMB polarization (B-modes) may provide a new window to confront more conventional models of inflation.