# 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.

Published Sep. 12, 2014 11:09 AM - Last modified Sep. 21, 2014 10:34 AM