The varying cosmological constant: a new approximation to the Friedmann equations and universe model
Abstract
We investigate the timedependent nature of the cosmological constant, Λ, of the Einstein Field Equation (EFE). Beginning with the EinsteinHilbert action as our fundamental principle we develop a modified version of the EFE allowing the value of Λ to vary as a function of time, Λ(t), indirectly, for an expanding universe. We follow the evolving Λ presuming fourdimensional spacetime and a flat universe geometry and present derivations of Λ(t) as functions of the Hubble constant, matter density, and volume changes which can be traced back to the radiation epoch. The models are more detailed descriptions of the Λ dependence on cosmological factors than previous, allowing calculations of the important parameters, Ω_{m} and Ω_{r}, to deep lookback times. Since we derive these without the need for extra dimensions or other special conditions our derivations are useful for model evaluation with astronomical data. This should aid resolution of several difficult problems of astronomy such as the best value for the Hubble constant at present and at recombination.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 May 2018
 DOI:
 10.1093/mnras/sty221
 Bibcode:
 2018MNRAS.476..451O
 Keywords:

 equation of state;
 cosmological parameters;
 dark energy;
 distance scale;
 cosmology: theory