# Cosmology seminar: Phillip Helbig

Phillip Helbig is now working in IT at the stock exchange after having worked for several years in cosmology.

**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

$\lambda_{0} \approx 0.7$ and $\Omega_{0} \approx 0.3$. 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 $\eta$ ($0 \le \eta \le 1$),

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.