  Weak lensing, which is the deflection of light by matter along the line of
sight, has proven to be an efficient method for constraining models of
structure formation and reveal the nature of dark energy. So far, most
weak-lensing studies have focused on the shear field that can be measured
directly from the ellipticity of background galaxies. However, within the
context of forthcoming full-sky weak-lensing surveys such as Euclid,
convergence maps (mass maps) offer an important advantage over shear fields in
terms of cosmological exploitation. While it carry the same information, the
lensing signal is more compressed in the convergence maps than in the shear
field. This simplifies otherwise computationally expensive analyses, for
instance, non-Gaussianity studies. However, the inversion of the non-local
shear field requires accurate control of systematic effects caused by holes in
the data field, field borders, shape noise, and the fact that the shear is not
a direct observable (reduced shear). We present the two mass-inversion methods
that are included in the official Euclid data-processing pipeline: the standard
Kaiser & Squires method (KS), and a new mass-inversion method (KS+) that aims
to reduce the information loss during the mass inversion. This new method is
based on the KS method and includes corrections for mass-mapping systematic
effects. The results of the KS+ method are compared to the original
implementation of the KS method in its simplest form, using the Euclid Flagship
mock galaxy catalogue. In particular, we estimate the quality of the
reconstruction by comparing the two-point correlation functions and third- and
fourth- order moments obtained from shear and convergence maps, and we analyse
each systematic effect independently and simultaneously...
