Gravitinos may explain early universe

17 Jun 2002

Recent measurements suggest that Big Bang nucleosynthesis (BBN) estimates for D and He-3 abundance in the cosmos are too high, and that the theory (or the observations) must be amended. BBN details how nuclei, especially deuterium, helium, and lithium, were made in the early minutes of the universe. Along with the microwave background and the mutual recession of galaxies, the observed abundance of primordial He, D, and Li is one of the chief supports of big bang cosmology.

Physicists at Berkeley and the University of Tokyo tackle this problem by invoking a hypothetical exotic particle. In an upcoming article in Physical Review Letters, the researchers theorize that the presence of such a particle with the right mass and lifetime in the early universe might, in the act of decaying, have provided a torrent of gamma rays. The gamma rays dismembered deuterium (into two hydrogens) and He-3 (into H and D), bringing their numbers into line with modern measurements. He-4, more tightly bound that He-3, would be relatively immune to the marauding gammas.

If this scenario is correct, the particle in question might well have been a "gravitino," the fermion cousin of the graviton. Gravitinos are ordained as part of "supersymmetry," a theory which holds that all known fermions (such as electrons or quarks) have hypothetical boson counterparts and vice versa.