  It has been shown that non-Abelian solitonic vortex string supported in
four-dimensional (4D) N=2 supersymmetric QCD (SQCD) with the U(2) gauge group
and $N_f=4$ quark flavors becomes a critical superstring. This string
propagates in the ten-dimensional space formed by a product of the flat 4D
space and an internal space given by a Calabi-Yau noncompact threefold, namely,
the conifold. The spectrum of low lying closed string states was found and
interpreted as a spectrum of hadrons in 4D N=2 SQCD. In particular, the lowest
string state appears to be a massless BPS baryon associated with the
deformation of the complex structure modulus $b$ of the conifold. It was
recently shown that the Coulomb branch of the associated string sigma model
which opens up at strong coupling can be described by N=2 Liouville theory.
Building on these results we switch on quark masses in 4D N=2 SQCD and study
the interpolation of the initial U(2) SQCD with $N_f=4$ quarks to the final
SQCD with the U(4) gauge group and $N_f=8$ quarks. To find the true string
vacuum which arises due to the mass deformation we solve the effective
supergravity equations of motion associated with the deformed world sheet
Liouville theory. We show that the massless BPS baryon $b$ survives the
deformation and that finding of the spectrum of low lying massive hadrons in
the final SQCD is linked to the Calogero problem.
