Light spin-1/2 or spin-0 dark matter particles

We recall and precise how light spin-0 particles could be acceptable dark matter candidates, and extend this analysis to spin-1/2 particles. We evaluate the (rather large) annihilation cross sections required, and show how they may be induced by a new light neutral spin-1 boson U. If this one is vectorially coupled to matter particles, the (spin-1/2 or spin-0) dark matter annihilation cross section into e(+)e(-) automatically includes a v(dm)(2) suppression factor at threshold, as desirable to avoid an excessive production of g rays from residual dark matter annihilations. We also relate dark matter annihilations with production cross sections in e(+)e(-) scatterings. Annihilation cross sections of spin-1/2 and spin-0 dark matter particles are given by exactly the same expressions. Just as for spin-0, light spin-1/2 dark matter particles annihilating into e(+)e(-) could be responsible for the bright 511 keV gamma ray line observed by INTEGRAL from the galactic bulge.