Abstract
In previous works, we have derived a Running Vacuum Model (RVM) for a string Universe, which provides an effective description of the evolution of 4-dimensional string-inspired cosmologies from inflation till the present epoch. In the context of this “stringy RVM” version, it is assumed that the early Universe is characterised by purely gravitational degrees of freedom, from the massless gravitational string multiplet, including the antisymmetric tensor field. The latter plays an important role, since its dual gives rise to a ‘stiff’ gravitational axion “matter”, which in turn couples to the gravitational anomaly terms, assumed to be non-trivial at early epochs. In the presence of primordial gravitational wave (GW) perturbations, such anomalous couplings lead to an RVM-like dynamical inflation, without external inflatons. We review here this framework and discuss potential scenarios for the generation of such primordial GW, among which the formation of unstable domain walls, which eventually collapse in a non-spherical-symmetric manner, giving rise to GW. We also remark that the same type of “stiff” axionic matter could provide, upon the generation of appropriate potentials during the post-inflationary eras, (part of) the Dark Matter (DM) in the Universe, which could well be ultralight, depending on the parameters of the string-inspired model. All in all, the new (stringy) mechanism for RVM inflation preserves the basic structure of the original (and more phenomenological) RVM, as well as its main advantages: namely, a mechanism for graceful exit and for generating a huge amount of entropy capable of explaining the horizon problem. It also predicts axionic DM and the existence of mild dynamical Dark Energy (DE) of quintessence type in the present universe, both being “living fossils” of the inflationary stages of the cosmic evolution. Altogether the modern RVM appears to be a theoretically sound (string-based) approach to cosmology with a variety of phenomenologically testable consequences.
Highlights
In the string-inspired effective gravitational field theory for the very early Universe, proposed in [1,2,3], and further discussed from the point of view of the swampland criteria and the weak gravity conjecture in [4], it was assumed that the only degrees of freedom present are those from the massless bosonic gravitational multiplet of thestring, consisting of dilaton, gravitons and antisymmetric tensor (Kalb–Ramond (KR)) fields
We propose the possibility that there is a pre-inflationary era of stiffaxionic-matter dominance, which upon condensation of primordial gravitational waves (GW), leads— through the gravitational anomalous couplings of the axions—to “stringy Running Vacuum Model (RVM)-inflation”
We discussed a stringy version of the Running-Vacuum-Model (RVM) (“stringy RVM”), which provides an effective description for the evolution of a string-inspired cosmological model from the Big-Bang to the present era
Summary
In the string-inspired effective gravitational field theory for the very early Universe, proposed in [1,2,3], and further discussed from the point of view of the swampland criteria and the weak gravity conjecture in [4], it was assumed that the only degrees of freedom present are those from the massless bosonic gravitational multiplet of the (super)string, consisting of dilaton, gravitons and antisymmetric tensor (Kalb–Ramond (KR)) fields. The original RVM[5,6,7,8,9,10,11]—see [12,13,14,15] for detailed reviews—constitutes a theoretically (renormalisation-group inspired) and phenomenologically compelling alternative to the standard concordance ΛCDM model, providing an effective description of the cosmological evolution of the Universe from inflation till the present era It helps alleviate the current tensions with the data, as shown in a variety of fitting analyses [22,23,24,25,26,27,28,29].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
