Vacuum Energy Density Measured from Cosmological Data

Abstract

Within the $\hat{I}›$CDM cosmological model, the absolute value of Einstein's cosmological constant $\hat{I}›$, sometimes expressed as the gravitating mass-energy density $\ddot{I}{}_{\hat{I}}›$ 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 $\hat{I}›$CDM cosmological model are used here to make a joint Bayesian inference on the combination of conventional parameters $\hat{I}{\text{c◯}}_{\hat{I}}›h^2$ that corresponds to the absolute physical density $\ddot{I}{}_{\hat{I}}›$. In physical units, we obtain $\ddot{I}{}_{\hat{I}}›=\left(60.3\pm 1.3\right)\times 10^{-31}g/c{\mathrm{m}}^3$, 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 $\hat{I}›$CDM model include constraints on the vacuum density.

8 + 11 pages, 4 figures. Published by JCAP