# Weak-lensing peak counts

### What are peak counts?

Weak-lensing peaks are local maxima of a lensing map. They are direct traces of dark-matter halos which are very massive structures in the Universe.

As the population of halos (mass function) depends strongly on cosmology, peaks help constraining cosmological parameters. Promising results from peaks have already been shown in literature.

### A new model for prediction

We have developped a prediction model for weak-lensing peak counts using a stochastic forward approach. The summary of the algorithm is as follows:

We have shown that in this way, the prediction agrees well with $N$-body simulations.

Three advantages can be outlined from this model:

• Fast - only few seconds for creating a 25-deg$^2$ field, without MPI or GPU programming
• Flexible - straightforward to include observational effects (e.g. photo-$z$ errors, masks) and additional features (e.g. intrinsic alignment, baryonic effects)
• Full PDF information - allow more flexible constraint methods such as varying covariances, $p$-value evaluation, approximate Bayesian computation, etc.