  Recently, Kaplan proposed an interesting extension of QCD named Extended QCD
or XQCD with bosonic auxiliary fields [1]. While its partition function is kept
exactly the same as that of QCD, XQCD naturally contains properties of
low-energy hadrons. We apply this extension to the two-dimensional QCD in the
large $N_c$ limit ('t Hooft model) [2]. In this solvable model, it is possible
to directly examine the hadronic picture of the 2d XQCD and analyze its
renormalization group flow to understand how the auxiliary degrees of freedom
behave in the low energy region. We confirm that the additional scalar fields
can become dynamical acquiring the kinetic term, and its parity-odd part
becomes dominant in the low energy region. This renomalization of XQCD provides
an "extension" of the renormalization scheme of QCD, inserting different field
variables from those in the original theory, without any changes in physical
observables.
