SUPERNOVA la CONSTRAINTS ON A TIME-VARIABLE COSMOLOGICAL “ CONSTANT”

摘要

The energy density of a scalar field Φ with potential V(Φ) ∝ Φ~-α, α ＞ 0, behaves like a time-variable cosmological constant that could contribute significantly to the present energy density. Predictions of this spatially flat model are compared to recent Type la supernova apparent magnitude versus redshift data. A large region of model parameter space is consistent with current observations. (These constraints are based on the exact scalar field model equations of motion, not on the widely used time-independent equation of state fluid approximation equations of motion.) We examine the consequences of also incorporating constraints from recent measurements of the Hubble parameter and the age of the uni- verse in the constant and time-variable cosmological constant models. We also study the effect of using a noninformative prior for the density parameter.