Repository logo

Graduated dark energy: Observational hints of a spontaneous sign switch in the cosmological constant

Accepted version



Change log


Akarsu, Ö 
Barrow, JD 
Escamilla, LA 
Vazquez, JA 


We study the cosmological constant in the standard CDM model by introducing the graduated dark energy (gDE) characterised by a minimal dynamical deviation from the null inertial mass density of the in the form inert / < 0 with < 1 being a ratio of two odd integers, for which its energy density dynamically takes negative values in the nite past. For large negative values of , it creates a phenomenological model described by a smooth function that approximately describes the spontaneously switching sign in the late universe to become positive today. We confront the model with the latest combined observational data sets of PLK+BAO+SN+H. It is striking that the data predict bimodal posterior probability distributions for the parameters of the model along with large negative values; the new maximum signi cantly excludes the , and the old maximum contains the . The improvement in the goodness of the t for the reaches highly signi cant levels, 2 min = 6:4, for the new maxima, while it remains at insigni cant levels, 2 min . 0:02, for the old maxima. We show that, in contrast to the old maxima, which do not distinguish from the , the new maxima agree with the model-independent H0 measurements, high-precision Ly- data, and model-independent Omh2 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 AdS vacua to dS vacua, at a redshift z 2:32 and triggered the late-time acceleration, and suggests looking for such mechanisms in string theory constructions.



5106 Nuclear and Plasma Physics, 5107 Particle and High Energy Physics, 51 Physical Sciences

Journal Title

Physical Review D

Conference Name

Journal ISSN


Volume Title



American Physical Society (APS)


All rights reserved
Science and Technology Facilities Council (ST/P000673/1)