  In a QCD-like string model based on D6 flavor branes in the presence of D4
color branes wrapping one of the compactified dimension on an $S^1$, the shape
of meson strings in the five dimensional curved space as well as the potential
between quark and anti-quark are investigated. The flavor branes on which both
ends of a meson string live are assumed to be separated in this five
dimensional space, depending on the values of the constituent quark masses. It
is shown in this picture that the meson string with different flavors on both
ends changes its shape at a critical distance. There is, however, no critical
distance for the meson with the same flavors. At this critical distance the
potential between quark and anti-quark with different flavors gives a point of
reflection and changes its shape around this point. Accordingly, the attractive
force between quark and anti-quark seems to become stronger when the distance
of flavor branes connecting meson strings becomes larger. This indicates quark
systems with different flavors can form high-density states.

High Energy Physics - Phenomenology