  The gravitational lensing signal produced by a galaxy or a galaxy cluster is
determined by its total matter distribution, providing us with a way to
directly constrain their dark matter content. State-of-the-art numerical
simulations successfully reproduce many observed properties of galaxies and can
be used as a source of mock observations and predictions. Many gravitational
lensing studies aim at constraining the nature of dark matter, discriminating
between cold dark matter and alternative models. However, many past results are
based on the comparison to simulations that did not include baryonic physics.
Here we show that the presence of baryons can significantly alter the
predictions: we look at the structural properties (profiles and shapes) of
elliptical galaxies and at the inner density slope of subhaloes. Our results
demonstrate that future simulations must model the interplay between baryons
and alternative dark matter, to generate realistic predictions that could
significantly modify the current constraints.
