working on fundamental physics at Heidelberg University, Zentrum für Astronomie. my scientific interests include cosmology, the formation and evolution of the cosmic large-scale structure, gravitational lensing and CMB-anisotropies as a probe of fundamental physics, and cosmostatistics

recent projects

intrinsic alignments

2017

Weak lensing operates under the assumption of intrinsically uncorrelated galaxy shapes, which might not be true because galaxies experience correlated tidal gravitational fields and share a similar angular momentum generation. We have worked on tidal interaction models for galaxies to derive ellipticity correlations for investigating their contaminating effect in weak lensing parameter inference. Starting from models of tidal shearing and tidal torquing for the orientation of elliptical and spiral galaxies, we are constructing more elaborate models for predicting and investigating intrinsic alignments.

integrated Sachs-Wolfe effect

2017

The iSW-effect is a secondary CMB-anisotropy and can be used to measure the equation of state of dark energy. Our results on the iSW-effect include the extension to nonlinearly evolving structures (Rees-Sciama-effect), the interpretation of the iSW-effect as a higher-order lensing phenomenon and cross-correlations with the weak lensing field. Using data from the European Planck-satellite, we have obtained independent measurements on the existence and properties of dark energy, in cooperation with P. Vielva (Santander) and C. Hernandez-Monteagudo (Teruel).

cosmic inflation

2017

Cosmic inflation is an early phase of accelerated expansion that solves the flatness-problem in FLRW-cosmologies and is a mechanism for introducing fluctuations in the distribution of matter. Of particular interest to us are inflationary non-Gaussianities and their measurement in future large-scale structure surveys. The best way of measuring higher-order non-Gaussianities is still unclear; while there is a clear way of computing polyspectra from covariant perturbation theory, their estimation from data quickly becomes a combinatorial problem, for which we use advanced sampling methods.

statistical inference and information geometry

2017

Modern cosmology is a statistical science and we are interested in questions related to the information content of large-scale structure surveys, in particular in the nonlinear regime, selection of models and the effect of systematical errors on the parameter estimation and model selection process. In particular, we investigate what properties about gravity are in principle knowable from cosmological surveys, how non-Gaussian structures can be described in an efficient way, how information about fundamental physics can be extracted from non-Gaussian structures (in cooperation with J. Hamann, Sydney), and how a non-ideal cosmological observer obtains biased measurements (with G.F. Lewis and K. Bolejko, Sydney).

constructive cosmology

2017

Constructive gravity asserts that there is a clear path of constructing a gravitational interaction for particles that is determined completely by their non-gravitational interactions. Our group works in cooperation with F.P. Schuller (Erlangen) and M.C. Werner (Kyoto) on cosmological tests of constructive gravity, and we work on astrophysical and cosmological applications of area-metric gravity.

Euclid

2015

The European Euclid mission is a space-based large-scale structure survey, where we are involved in the weak lensing programme, where we construct and test models of intrinsic alignments of galaxies, which result due to tidal interaction with the large-scale structure or by correlations in the initial conditions of structure formation. In addition, our group was active in computing second order effects in gravitational lensing, parameter estimation biases and the information content of Gaussian and non-Gaussian weak lensing maps.

weak gravitational lensing

2009

Weak lensing refers to the weak distortion of the light bundles reaching us from distant galaxies caused by tidal gravitational fields in the cosmic large-scale structure. Weak lensing is an excellent tool for investigating gravity on large scales, and we have worked on tomographic methods, cross-correlations and higher-order statistics of the weak lensing signal, as well as effects gravitational light deflection at second order.