Abstract
We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry in the cosmos, but also provide time-dependent contributions to the vacuum energy density of ``running-vacuum'' type, which drive the Universe's evolution. According to this scenario, during the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induces gravitational anomalies, which couple to the [Kalb-Ramond (KR)] axion field emerging from the antisymmetric tensor field of the massless gravitational multiplet of the string. Such anomalous $CP$-violating interactions have two important effects. First, they lead to contributions to the vacuum energy density of the form appearing in the ``running vacuum model'' (RVM) framework, which are proportional to both, the square and the fourth power of the effective Hubble parameter, ${H}^{2}$ and ${H}^{4}$ respectively. The ${H}^{4}$ terms may lead to inflation, in a dynamical scenario whereby the role of the inflaton is played by the effective scalar-field (``vacuumon'') representation of the RVM. Second, there is an undiluted KR axion at the end of inflation, which plays an important role in generating matter-antimatter asymmetry in the cosmos, through baryogenesis via leptogenesis in models involving heavy right-handed neutrinos. As the Universe exits inflation and enters a radiation-dominated era, the generation of chiral fermionic matter is responsible for the cancellation of gravitational anomalies, thus restoring diffeomorphism invariance for the matter/radiation (quantum) theory, as required for consistency. Chiral U(1) anomalies may remain uncompensated, though, during matter/radiation dominance, providing RVM-like ${H}^{2}$ and ${H}^{4}$ contributions to the Universe energy density. Finally, in the current era, when the Universe enters a de Sitter phase again, and matter is no longer dominant, gravitational anomalies resurface, leading to RVM-like ${H}^{2}$ contributions to the vacuum energy density, which are however much more suppressed, as compared to their counterparts during inflation, due to the smallness of the present era's Hubble parameter ${H}_{0}$. In turn, this feature endows the observed dark energy with a dynamical character that follows the RVM pattern, a fact which has been shown to improve the global fits to the current cosmological observations as compared to the concordance $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model with its rigid cosmological constant, $\mathrm{\ensuremath{\Lambda}}>0$. Our model favors axionic dark matter, the source of which can be the KR axion. The uncompensated chiral anomalies in late epochs of the Universe are argued to play an important role in this, in the context of cosmological models characterized by the presence of large-scale cosmic magnetic fields at late eras.
Highlights
AND MOTIVATION: RUNNING VACUUM MODEL FOR THE UNIVERSEOver the last two decades, a plethora of cosmological observations [1] have drastically changed our perception of the Universe
In this article we have provided a string-inspired theoretical framework in which, during the early phase of the Universe, there are important contributions to the vacuum energy density which are related to the CP-violating gravitational anomalies of a primordial space-time of string theory
The gravitational anomalies, whose presence in general would cause diffeomorphism-invariance breaking in the quantum theory, do not constitute any inconsistency, as would be the case if matter were present, since the anomalies describe the exchange of energy solely among gravitational d.o.f
Summary
Over the last two decades, a plethora of cosmological observations [1] have drastically changed our perception of the Universe. III A that, in the radiation or matter era, after the exit from inflation, the generation of chiral matter would lead to a cancellation of gravitational anomalies, as would be “conventionally” required for the “consistency” of the matter and radiation quantum field theory, without the need to employ a generalized stress-energy tensor [Eq (39)] In such a case, the axion fields would only couple at most to chiral or in general triangle anomalies, which do not contribute to the stress tensor, due to their topological form [see the discussion in Sec. III A, after Eq (99)], and, the conventional local covariant conservation of the matter/radiation stress tensor is guaranteed for any metric background.
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.
