  The electroweak Higgs boson has been discovered in ongoing experiments at the
LHC, leading to a mass of this particle of 126 GeV. This Higgs boson mediates
the generation of mass for elementary particles, including the mass of
elementary (current) quarks. These current-quark masses leave 98% of the mass
of the atom unexplained. This large fraction is mediated by strong interaction,
where instead of the Higgs boson the $\sigma$ meson is the mediating particle.
Though already discovered in 1957 by Schwinger, the $\sigma$ meson has been
integrated out in many theories of hadron properties because it had not been
observed and was doubted to exist. With the observation of the $\sigma$ meson
in recent experiments on Compton scattering by the nucleon at MAMI (Mainz) it
has become timely to review the status of experimental and theoretical
researches on this topic.
