  The perfect fit of the matter fields of the Standard Model (SM) into the
$SU(5)$ multiplets has strongly supported the idea of the Grand Unified Theory
(GUT) for decades. In this paper, we discuss a novel framework which explains
why the SM matter fields form the apparently complete $SU(5)$ multiplets. In
the new framework, the apparent matter unification inevitably results from
chiral $SU(5)$ gauge theory even if the quarks and leptons are not embedded
into the common $SU(5)$ multiplets. We call this class of models the "fake
GUT". The novel phenomenological prediction of the fake GUT is more variety of
the nucleon decay modes than the conventional GUT, which reflects the rich
structure of the origin of the matter fields.

High Energy Physics - Phenomenology