Kleidis, KostasKuiroukidis, ApostolosPapadopoulos, Demetrios B.Verdaguer, Enric2015-06-162024-09-272015-06-162024-09-272011-09-15http://journals.aps.org/prd/abstract/10.1103/PhysRevD.84.124044https://repository2024.ihu.gr/handle/123456789/1313In a previous paper [K. Kleidis, D. B. Papadopoulos, E. Verdaguer, and L. Vlahos, Phys. Rev. D 78, 024027 (2008).] we considered the possibility that (within the early-radiation epoch) there has been (also) a short period of a significant presence of cosmic strings. During this radiation-plus-strings stage the Universe matter-energy content can be modeled by a two-component fluid, consisting of radiation (dominant) and a cosmic-string fluid (subdominant). It was found that, during this stage, the cosmological gravitational waves—that had been produced in an earlier (inflationary) epoch—with comoving wave numbers below a critical value (which depends on the physics of the cosmic-string network) were filtered, leading to a distorsion in the expected (scale-invariant) cosmological gravitational wave power spectrum. In any case, the cosmological evolution gradually results in the scaling of any long-cosmic-string network and, hence, after a short time interval, the Universe enters into the late-radiation era. However, along the transition from an early-radiation epoch to the late-radiation era through the radiation-plus-strings stage, the time dependence of the cosmological scale factor is modified, something that leads to a discontinuous change of the corresponding scalar curvature, which, in turn, triggers the quantum-mechanical creation of gravitons. In this paper we discuss several aspects of such a process, and, in particular, the observational consequences on the expected gravitational-wave power spectrum.enAttribution-NonCommercial-NoDerivatives 4.0 Διεθνέςhttp://creativecommons.org/licenses/by-nc-nd/4.0/Άρθρο σε επιστημονικό περιοδικό10.1103/PhysRevD.84.124044