  After taking into account both the pion and sigma meson exchange potential,
we have performed a dynamical calculation of the $D^0\bar{D}^{\ast0}$ system.
The $\sigma$ meson exchange potential is repulsive from heavy quark symmetry
and numerically important for a loosely bound system. Our analysis disfavors
the interpretation of X(3872) as a loosely bound molecular state if we use the
experimental $D^\ast D\pi$ coupling constant $g=0.59$ and a reasonable cutoff
around 1 GeV, which is the typical hadronic scale. Bound state solutions with
negative eigenvalues for the $D\bar{D}^\ast$ system exist only with either a
very large coupling constant (two times of the experimental value) or a large
cutoff ($\Lambda \sim 6$ GeV or $\beta \sim 6$ GeV$^2$). In contrast, there
probably exists a loosely bound S-wave $B\bar{B}^\ast$ molecular state. Once
produced, such a molecular state would be rather stable since its dominant
decay mode is the radiative decay through $B^\ast\to B \gamma$. Experimental
search of these states will be very interesting.

High Energy Physics - Phenomenology;High Energy Physics - Experiment;High Energy Physics - Lattice;Nuclear Theory