PhD defense by Jeppe Trøst Nielsen – University of Copenhagen

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PhD defense by Jeppe Trøst Nielsen

Title:Testing Cosmological Models

The concordance model of cosmology is remarkable for its apparent simplicity, and vast range of predictions. Yet its two most well known and infamous ingredients, dark energy and inflation, have so far avoided all attempts at direct observation. Even so, theorists invent ever more exotic models, and experiments must keep up at an ever increasing pace, preserving both precision and accuracy in the analysis.

In this thesis I compute corrections to large scale structure observables, corrections we expect solely due to general relativity. The calculations can be perceived in two ways. The pessimist will say these effects are unwanted systematics in the search for primordial physics, the optimist will see it as a chance to test general relativity to ever increasing precision. Regardless, these effects must be computed as part of the interpretation of coming observations.


I calculate the predicted bispectrum in galaxy number counts from general relativistic effects. This includes in particular lensing, which will systematically shift the observed bispectrum for observations of large scale structure. Furthermore, I develop and explore a scheme for fast computation of the galaxy number count spectra, in the flat-sky approximation.


The last part of the work is a numerical analysis of the resulting spectra. I analyse both the potential observability of individual bispectra, and their correction due to general relativistic effects. It is clear from the results that lensing must be carefully included in any attempt at accurately extracting primordial bispectra.