Possible DDˉD\bar{D} and BBˉB\bar{B} Molecular states in a chiral quark model

We perform a systematic study of the bound state problem of $D\bar{D}$ and $B\bar{B}$ systems by using effective interaction in our chiral quark model. Our results show that both the interactions of $D\bar{D}$ and $B\bar{B}$ states are attractive, which consequently result in $I^G(J^{PC})=0^+(0^{++})$ $D\bar{D}$ and $B\bar{B}$ bound states.Comment: arXiv admin note: substantial text overlap with arXiv:1204.395

Once again: Instanton method vs. WKB

A recent analytic test of the instanton method performed by comparing the exact spectrum of the Lam${\acute e}$ potential (derived from representations of a finite dimensional matrix expressed in terms of $su(2)$ generators) with the results of the tight--binding and instanton approximations as well as the standard WKB approximation is commented upon. It is pointed out that in the case of the Lam${\acute e}$ potential as well as others the WKB--related method of matched asymptotic expansions yields the exact instanton result as a result of boundary conditions imposed on wave functions which are matched in domains of overlap.Comment: 10 pages, no figures. References list revised according to JHE