Nearly massless axion-like particles are of interest for astrophysical
observations, and some constraints on their parameter space do exist in the
literature. Here, we propose to put new constraints on these particles using
polarisation and, in particular, the polarisation differences observed between
different quasar classes.Comment: Contributed to the "7th Patras Workshop on Axions, WIMPs and WISPs",
Mykonos June 26 - July 1 201
