Hitoshi Murayama

Cosmological constraints on the light stable gravitino

Abstract Cosmological constraints when the gravitino is the lightest superparticle are studied. From the condition that the relic gravitinos should not overclose the universe, the upper bound on the reheating temperature of the universe is found to be 102–1010 GeV in a range of gravitino mass 10−5–10 GeV. Furthermore, if the decay of the next-to-the-lightest superparticle produces sizable high energy photons, constraints from the light element (D, 3He, 4He) photodestruction exclude a range of the gravitino mass.

Probing the symmetry-breaking pattern using sfermion masses

Abstract We study the mass spectrum of superparticles within supersymmetric grand unified models. For gaugino masses, it is pointed out that the GUT relation in the SU (5) model is applicable to a more general case where a grand-unified gauge group breaks dowm to the standard model gauge group by several steps. We also show that the mass spectrum of squarks and sleptons carries the information on the breaking pattern of the gauge symmetry. It is demonstrated in some SO (10) models how the scalar mass spectrum distinguishes various SO (10) breaking patterns from each other.

NEUTRINO DARK MATTER WITH A GALACTIC-RANGE NEW FORCE

We propose a new force of the galactic range acting among massive neutrinos to weaken the phase space constraint for the neutrino dark halo. As a consequence we find that the neutrino with mass 10 eV becomes a candidate for the galaxy dark halo to explain the observed flat rotation curves. Cosmological consequence of the new force is briefly discussed. It is, furthermore, pointed out that the new force can be naturally incorporated into the see-saw model for the neutrino mass.

Weinberg angle without grand unification.

We assume that strong and electroweak interactions become strong at very high energies. With this assumption, we compute the low-energy gauge coupling constants [alpha][sub [ital i]]([ital m][sub [ital Z]]) as a function of the cutoff scale, taking the supersymmetric standard model with 3+2[ital n] families of quark and lepton multiplets. We find that only the five-family case ([ital n]=1) is consistent with the experimental values of the gauge coupling constants. This suggests the presence of a pair of families at [similar to]1 TeV.