First evidence of running cosmic vacuum: challenging the concordance model (1602.02103v5)

Abstract: Despite the fact that a rigid $\Lambda$-term is a fundamental building block of the concordance $\Lambda$CDM model, we show that a large class of cosmological scenarios with dynamical vacuum energy density $\rho_{\Lambda}$ and/or gravitational coupling $G$, together with a possible non-conservation of matter, are capable of seriously challenging the traditional phenomenological success of the $\Lambda$CDM. In this paper, we discuss these "running vacuum models" (RVM's), in which $\rho_{\Lambda}=\rho_{\Lambda}(H)$ consists of a nonvanishing constant term and a series of powers of the Hubble rate. Such generic structure is potentially linked to the quantum field theoretical description of the expanding Universe. By performing an overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+BBN+CMB$ (in which the WMAP9, Planck 2013 and Planck 2015 data are taken into account), we find that the class of RVM's appears significantly more favored than the $\Lambda$CDM, namely at an unprecedented level of $\gtrsim4.2\sigma$. Furthermore, the Akaike and Bayesian information criteria confirm that the dynamical RVM's are strongly preferred as compared to the conventional rigid $\Lambda$-picture of the cosmic evolution.

Evidence of Dynamical Cosmic Vacuum: A Statistical Challenge to ΛCDM

The paper presents an analytical and observational paper on dynamical vacuum models, termed running vacuum models (RVMs), and their capacity to challenge the conventional ΛCDM model. The authors demonstrate that a dynamically evolving cosmic vacuum energy density and gravitational couplings, considered broadly within the framework of quantum field theory (QFT) in curved spacetime, can provide a superior fit to cosmological observations compared to the traditionally static Λ-term of the ΛCDM model.

Main Findings and Methodology

The central thesis of the paper is the exploration of the RVMs, where the vacuum energy density is described as a function comprising a constant term and powers of the Hubble rate, H(t). The gravitational coupling, G, is also treated as a variable dependent on the cosmic expansion rate. To test these models, the authors use a comprehensive set of cosmological data, including SNIa, BAO, H(z), LSS, BBN, and CMB observations, integrating data from major surveys and compilations such as Planck and WMAP.

Strong statistical evidence supports the RVMs over the ΛCDM model. The level of statistical significance reached in this analysis is notable, with a reported preference for RVMs over ΛCDM at a level greater than 4σ. Detailed fits to the observed data reveal that RVM models are markedly favored over the ΛCDM when evaluated using information criteria like AIC and BIC, with ΔAIC and ΔBIC values consistently indicating strong evidence against the ΛCDM.

Implications of the Study

The implications of this research are profound both theoretically and practically. Theoretically, the paper opens avenues for further exploration of quantum effects on the cosmological evolution, addressing one of the significant theoretical conundrums, the old cosmological constant problem. Practically, the evidence supporting dynamical vacuum models suggests a need to revisit canonical assumptions regarding dark energy and the expansion dynamics of the Universe. This could lead to refined predictive models that better align theory with observational data.

The authors take a meticulous approach to model fitting, ensuring the choice of data sets, and their combinations are such that offer the most robust testing grounds for their hypothesis. The combination of high-quality BAO, LSS, and CMB data contributes significantly to their findings, underscoring the importance of using comprehensive datasets in cosmological research.

Prospects for Future Research

Looking ahead, the characterization of cosmic vacuum dynamics as proposed by the RVMs could spearhead new theoretical directions or extensions to general relativity and quantum field theories. It may also foster greater integration between cosmological data and particle physics experiments, particularly in areas studying quantum gravity effects and fundamental forces in the Universe.

Observationally, upcoming surveys with higher precision, such as those from the European Euclid mission or the Vera Rubin Observatory, could further test and refine these findings. Advances in AI and computational methods could also enhance data modeling and integration techniques, providing clearer insights into the nature of cosmic vacuum dynamics.

Conclusion

This paper makes significant strides toward understanding the evolution of the Universe and provides compelling evidence against the static vacuum assumption of the ΛCDM model. By leveraging a rigorous analysis and high-quality datasets, the authors convincingly advocate for the potential dominance of running vacuum models in describing cosmic evolution, marking a pivotal step in cosmological research.