  Accretion of fields by black holes is a subject of great interest in physics.
It is known that accretion plays a fundamental role in active galactic nuclei
and in the evolution of black holes. Accretion of fundamental fields is often
related to the study of absorption cross section. Basically all black holes for
which absorption of fields has been studied so far present singularities.
However, even within general relativity, it is possible to construct regular
black holes: objects with event horizons but without singularities. Many
physically motivated regular black hole solutions have been proposed in the
past years, demanding the understanding of their absorption properties. We
study the absorption of planar massless scalar waves by Bardeen regular black
holes. We compare the absorption cross section of Bardeen and
Reissner--Nordstr\"om black holes, showing that the former always have a bigger
absorption cross section for fixed values of the field frequency and of the
normalized black hole charge. We also show that it is possible for a Bardeen
black hole to have the same high-frequency absorption cross section of a
Reissner--Nordstr\"om black hole. Our results suggest that, in
mid-to-high-frequency regimes, regular black holes can have compatible
properties with black holes with singularities, as far as absorption is
concerned.

General Relativity and Quantum Cosmology