Cosmology seminar: Claudio Llinares: What scalar fields can say about the shape of dark matter halos

 Scalar fields are still not observed in nature.  Nevertheless there is
an increasing interest in the possibility that they do actually exist
and that they can explain the accelerated expansion of the universe.  At
present, there is a broad spectrum of theories that fulfill this
requirement and at the same time have no effects at very small scales,
which makes them able to pass solar system tests.  In order to test if
these scalar fields indeed exist, we need to find predictions at
intermediate scales in between those involved in the expansion of the
universe and the solar system (i.e. galaxies and galaxy clusters
scales).  I will summarize some of the properties of two particular
families of scalar-tensor theories (symmetron and chameleon models) and
I will show why observations of the shape of dark matter halos could
help to distinguish between them.