The m-z relation for Type Ia supernovae, locally inhomogeneous cosmological models, and the nature of dark matter

The m-z relation for Type Ia supernovae is one of the key pieces of evidence supporting the cosmological `concordance model' with λ[SUB]0[/SUB] ≈ 0.7 and Ω[SUB]0[/SUB] ≈ 0.3. However, it is well known that the m-z relation depends not only on λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] (with H[SUB]0[/SUB] as a scale factor) but also on the density of matter along the line of sight, which is not necessarily the same as the large-scale density. I investigate to what extent the measurement of λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] depends on this density when it is characterized by the parameter η (0 ≤ η ≤ 1), which describes the ratio of density along the line of sight to the overall density. I also discuss what constraints can be placed on η, both with and without constraints on λ[SUB]0[/SUB] and Ω[SUB]0[/SUB] in addition to those from the m-z relation for Type Ia supernovae.