Supernovae as probes of cosmic parameters: estimating the bias from under-dense lines of sight

Understand

Correctly interpreting observations of sources such as type Ia supernovae (SNe Ia) require knowledge of the power spectrum of matter on AU scales - which is very hard to model accurately.

• Because under-dense regions account for much of the volume of the universe, light from a typical source probes a mean density significantly below the cosmic mean.
• The relative sparsity of sources implies that there could be a significant bias when inferring distances of SNe Ia, and consequently a bias in cosmological parameter estimation.
• While the weak lensing approximation should in principle give the correct prediction for this, linear perturbation theory predicts an effectively infinite variance in the convergence for ultra-narrow beams.