Cosmological properties of a class ofΛdecaying cosmologies

We investigate some properties of flat cosmological models with a Λ term that decreases with time as Λ∝a^-m $(a$ is the scale factor and m is a parameter $0<~m<3)$. The models are equivalent to standard cosmology with matter and radiation plus an exotic fluid with the equation of state pₓ=(m/3-1)ρₓ. We study the effect of the decaying Λ term on the cosmic microwave background anisotropy and by using a seminumeric method we compute the angular power spectrum (up to $l=20)$ for different values of m and Ωₘ₀. We also investigate the constraints imposed on the models by the magnitude-redshift test in which high-redshift type Ia supernovae (SNe Ia) are used as standard candles. We obtain the $95.4%$, $90%,$ and $68%$ confidence levels on the parameters m and Ωₘ₀ and compare them with those arising from lensing statistics. Our analysis reveals that the SNe Ia constraints are stronger for low values of m and Ωₘ₀, while those from lensing statistics are more important for m1. Models with Ωₘ₀0.2 and m1.6 are in good agreement with the data.