Elusive exotic states

The existence of flavor exotic $QQ\bar{q}\bar{q}$ molecular-type states is investigated. An attractive force between two {\it pseudoscalar} $H = (Q\bar{q})$ heavy meson is generated by (correlated) two-pion exchange. The emergence of a (loosely) bound state depends crucially on the value of the coupling constant $g$ of the $H^*H\pi$ vertex. For a $g$ value calculated from the experimental upper limit on the width of the $D^*$ meson the considered mechanism alone is strong enough to generate a bound state in the $BB$ system while the $DD$ system is very close to become bound. Such states, if exist, are stable with respect to strong interactions. They may be observed as stable scalar particles with the mass $M\approx 2\,m_H$ and flavor quantum number $\pm 2$.Comment: 10 pages including 4 figures. RevTex and epsfig.sty are used. Accepted for publication in Phys. Lett.

Factorization Contributions and the Breaking of the ΔI=1/2\Delta I=1/2 Rule in Weak ΛNρ\Lambda N\rho and ΣNρ\Sigma N\rho Couplings

We compute the modified factorization contributions to the $\Lambda\rightarrow N\rho$ and $\Sigma\rightarrow N\rho$ couplings and demonstrate that these contributions naturally include $\Delta I=3/2$ terms which are comparable ($\simeq 0.4$ to $-0.8$ times) in magnitude to the corresponding $\Delta I=1/2$ terms. As a consequence, we conclude that models which treat vector meson exchange contributions to the weak conversion process $\Lambda N\rightarrow NN$ assuming such weak couplings to satisfy the $\Delta I=1/2$ rule are unlikely to be reliable.Comment: 13 pages, uses REVTEX Entire manuscript available as a ps file at http://www.physics.adelaide.edu.au/theory/home.html . Also available via anonymous ftp at ftp://adelphi.adelaide.edu.au/pub/theory/ADP-95-5.T172.ps To appear in Physical Review