Cosmological tests of Everpresent Λ

Everpresent Λ is a cosmological scenario in which the observed cosmological 'constant' Λ fluctuates between positive and negative values with a vanishing mean, and with a magnitude comparable to the critical density at any epoch. In accord with a longstanding heuristic prediction of causal set theory, it postulates that Λ is a stochastic function of cosmic time that will vary from one realization of the scenario to another. Herein, we consider two models of 'dark energy' that exhibit these features. Via Monte Carlo Markov chains, we explore the space of cosmological parameters and the set of stochastic realizations of these models, finding that Everpresent Λ can fit current cosmological observations as well as the ΛCDM model does. Furthermore, it removes the observational tensions that ΛCDM experiences in relation to low redshift measurements of the Hubble constant, and to the baryonic acoustic oscillations (BAO) in Lyman-α forest at -3. It does not, however, help significantly with the early growth of ultramassive black holes, or with the Lithium problem in Big Bang nucleosynthesis. Future measurements of 'dark energy' at high redshifts will further test the viability of Everpresent Λ as an alternative to the ΛCDM cosmology.