Graduated dark energy: Observational hints of a spontaneous sign switch in the cosmological constant
Abstract
We study the cosmological constant (Λ ) in the standard Λ cold dark matter model by introducing the graduated dark energy (gDE) characterized by a minimal dynamical deviation from the null inertial mass density of the Λ in the form ρinert∝ρλ<0 with λ <1 being a ratio of two odd integers, for which its energy density ρ dynamically takes negative values in the finite past. For large negative values of λ , it creates a phenomenological model described by a smooth function that approximately describes the Λ spontaneously switching sign in the late Universe to become positive today. We confront the model with the latest combined observational datasets of Planck +baryon acoustic oscillations +supernova +H . It is striking that the data predict bimodal posterior probability distributions for the parameters of the model along with large negative λ values; the new maximum significantly excludes the Λ , and the old maximum contains the Λ . The improvement in the goodness of fit for the Λ reaches highly significant levels, Δ χmin2=6.4 , for the new maxima, while it remains at insignificant levels, Δ χmin2≲0.02 , for the old maxima. We show that, in contrast to the old maxima, which do not distinguish from the Λ , the new maxima agree with the model-independent H0 measurements, high-precision Ly -α data, and model-independent O m h2 diagnostic estimates. Our results provide strong hints of a spontaneous sign switch in the cosmological constant and lead us to conjecture that the Universe has transitioned from anti-de Sitter vacua to de Sitter vacua, at a redshift z ≈2.32 , and triggered the late-time acceleration, and suggests looking for such mechanisms in string theory constructions.
- Publication:
-
Physical Review D
- Pub Date:
- March 2020
- DOI:
- 10.1103/PhysRevD.101.063528
- arXiv:
- arXiv:1912.08751
- Bibcode:
- 2020PhRvD.101f3528A
- Keywords:
-
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- General Relativity and Quantum Cosmology;
- High Energy Physics - Phenomenology;
- High Energy Physics - Theory
- E-Print:
- 14 pages, 7 figures, 2 tables