Small exotic molecules with bosonic constituents

We study the stability and the properties of the ground state of neutral systems containing up to four positively charged bosons and their antiparticles. Examples are the di-pionium molecule (π+ π-)2, which is almost identical to the positronium molecule (e+e-)2, the tri-pionium (π+π- )3, and the quadri-pionium (π+π-)4 molecules. We briefly compare our results on the energy to those on the large-N limit of (π+π-)N. We also show that the annihilation probability can be calculated accurately with simple wave functions when one uses the generalized Schwinger rule. (author)