Varying Lambda Theory Revisited

摘要

We revisit the variable. theory recently developed by Alexander et al. [1, 2]. We implement it to explain the current expansion of the Universe. The varying. theory reduces one degree of freedom. The varying. term (cosmological term) follows the energy density of the Universe. We consider such a theory which does not respect self-dual symmetry. The Bianchi identity enforces the. term to be a constant for a theory without torsion. However, torsion can incorporate a varying. term in the action. We consider a form of the action which has such a varying Lambda term, and the presence of only nonrelativistic matter energy density. We fit the luminosity distance according to the model and compare it with that in the Lambda CDM model and find their close behavior. However, we find a current value of matter energy density rho(m0) larger than the critical energy density. Using the supernova data from Union 2.1 compilation, we further consider a different set of parameters, for which kappa rho(m0)/3H(0)(2) becomes close to unity but, however, greater. For this set of parameters, we find a negative value in the effective equation of state, however, the model has a very different pattern of the Hubble parameter from the standard scenario.