  PAMELA and, more recently, AMS-02, are ushering us into a new era of greatly
reduced statistical uncertainties in experimental measurements of cosmic-ray
fluxes. In particular, new determinations of traditional diagnostic tools such
as the boron-to-carbon ratio (B/C) are expected to significantly reduce errors
on cosmic-ray diffusion parameters, with important implications for
astroparticle physics, ranging from inferring primary source spectra to
indirect dark matter searches. It is timely to stress, however, that the
conclusions obtained crucially depend on the framework in which the data are
interpreted as well as from some nuclear input parameters. We aim at assessing
the theoretical uncertainties affecting the outcome, with models as simple as
possible while still retaining the key dependencies. We compare different
semi-analytical, two-zone model descriptions of cosmic-ray transport in the
Galaxy. We test for the effect of a primary source contamination in the boron
flux by parametrically altering its flux, as well as for nuclear cross section
uncertainties. Our study on preliminary results from AMS-02 suggests that,
differently for instance from the leptonic case, realistic modelling of the
geometry of the Galaxy and of the source distribution are of minor importance
to correctly reproduce B/C data at high energies and thus, to a large extent,
for the extraction of diffusion parameters. The Ansatz on the lack of primary
injection of boron represents the most serious bias, and requires
multi-messenger studies to be addressed. If this uncertainty could be lifted,
nuclear uncertainties would still represent a serious concern, which degrade
the systematic error on the inferred parameters to the 20% level, or three
times the estimated experimental sensitivity. In order to reduce this, a new
nuclear cross section measurement campaign is probably required.

High Energy Astrophysical Phenomena