  In the case of three quark flavors, (pseudo)scalar diquarks transform as
antiquarks under chiral transformations. We construct four spin-1/2 baryonic
multiplets from left- and right-handed quarks as well as left- and right-handed
diquarks. The fact that two of these multiplets transform in a "mirror" way
allows for chirally invariant mass terms. We then embed these baryonic
multiplets into the Lagrangian of the so-called extended Linear Sigma Model,
which features (pseudo)scalar and (axial-)vector mesons, as well as glueballs.
Reducing the Lagrangian to the two-flavor case, we obtain four doublets of
nucleonic states. These mix to produce four experimentally observed states with
definite parity: the positive-parity nucleon $N(939)$ and Roper resonance
$N(1440)$, as well as the negative-parity resonances $N(1535)$ and $N(1650)$.
We determine the parameters of the nucleonic part of the Lagrangian from a fit
to masses and decay properties of the aforementioned states. Studying the limit
of vanishing quark condensate, we conclude that $N(939)$ and $N(1535)$, as well
as $N(1440)$ and $N(1650)$ form pairs of chiral partners.
