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 lambda(0) approximate to 0.7 and Omega(0) approximate to 0.3. However, it is well known that the m-z relation depends not only on lambda(0) and Omega(0) (with H-0 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 lambda(0) and Omega(0) depends on this density when it is characterized by the parameter eta (0 <= eta <= 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 eta, both with and without constraints on lambda(0) and Omega(0) in addition to those from the m-z relation for Type Ia supernovae.