Robust cosmological constraints on axion-like particles
  Axion-like particles with masses in the keV-GeV range have a profound impact
on the cosmological evolution of our Universe, in particular on the abundance
of light elements produced during Big Bang Nucleosynthesis. The resulting
limits are complementary to searches in the laboratory and provide valuable
additional information regarding the validity of a given point in parameter
space. A potential drawback is that altering the cosmological history may
potentially weaken or even fully invalidate these bounds. The main objective of
this article is therefore to evaluate the robustness of cosmological
constraints on axion-like particles in the keV-GeV region, allowing for various
additional effects which may weaken the bounds of the standard scenario.
Employing the latest determinations of the primordial abundances as well as
information from the cosmic microwave background we find that while bounds can
indeed be weakened, very relevant robust constraints remain.
