New constraints on very light pseudoscalars
  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. 
A. Payez, J. R. Cudell, D. Hutsem\'ekers
astro-ph.CO