Possible manifestations of the existence of a fourth-generation neutrino

A fourth generation of fermions predicted by the phenomenological heterotic string models can possess a new, strictly conserved charge. Among other th ings, this leads to the hypothesis of the existence of a fourth massive sta ble neutrino. A comparison of this hypothesis with the data obtained in the DAMA underground experiment to search for massive weakly-interacting cosmi c particles with hidden mass and with the EGRET measurements of the >1 GeV galactic gamma-ray background gives a value m approximate to 50 GeV for the possible mass of the fourth neutrino. It is shown that the hypothesis can be checked in accelerator experiments. The positron signal from annihilatio n of massive relic neutrinos in the galaxy is calculated. A search for this signal is is within the reach of planned cosmic-ray investigations. (C) 19 99 American Institute of Physics. [S0021-3640(99)00206-6].