Generalized Chen-Wu type cosmological model

Recent measurements require modifications in conventional cosmology by way of introducing components other than ordinary matter into the total energy density in the universe. On the basis of some dimensional considerations in line with quantum cosmology, Chen and Wu [W. Chen and Y. Wu, Phys. Rev. D 41, 695 (1990)] have argued that an additional component, which corresponds to an effective cosmological constant $\Lambda ,$ must vary as $a^{-2}$ in the classical era. Their decaying-$\Lambda$ model assumes inflation and yields a value for $q_0,$ which is not compatible with observations. We generalize this model by arguing that the Chen-Wu ansatz is applicable to the total energy density of the universe and not to $\Lambda$ alone. The resulting model, which has a coasting evolution (i.e., $a\propto t),$ is devoid of the problems of horizon, flatness, monopole, cosmological constant, size, age and generation of density perturbations. However, to avoid serious contradictions with big bang nucleosynthesis, the model has to make the predictions ${\Omega }_m=4/3\mathrm{}$ and ${\Omega }_{\Lambda }=2/3,$ which in turn are at variance with current observational values.