Vacuum Energy Density Measured from Cosmological Data

Within the $Λ$CDM cosmological model, the absolute value of Einstein's cosmological constant $Λ$, sometimes expressed as the gravitating mass-energy density $ρ_Λ$ of the physical vacuum, is a fundamental constant of nature, whose accurate measurement plays a central role in testing some proposed theories of quantum gravity. Several combinations of currently public cosmological data and an assumed flat $Λ$CDM cosmological model are used here to make a joint Bayesian inference on the combination of conventional parameters $Ω_Λh^2$ that corresponds to the absolute physical density $ρ_Λ$. In physical units, we obtain $ρ_Λ= \left(60.3\pm{1.3}\right)\times 10^{-31}{\rm g/cm^3}$, the most accurate constraint to date, with an absolute calibration of cosmological measurements based on CMB temperature. Significantly different values are obtained with calibrations that use a local distance scale, mainly connected to systematic differences in the value of the Hubble constant. It is suggested that future comprehensive cosmological parameter studies assuming the $Λ$CDM model include constraints on the vacuum density.

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