Neutralino States Research Articles

SUSY GUTs dark matter

We examine the cosmology of the lightest neutralino (χ) in a minimal SUSY GUT model. Our analysis incorporates the ensuing relations among the squark, slepton, and gaugino masses, and takes into account the recent experimental constraints on the parameter space. We consider a general neutralino state and compute its cosmological relic density resulting from pair annihilation into all allowed final states. Our analysis reveals a rich structure of resonances due to s-channel exchanges, and shows that some previous studies using pure neutralino states in “nearly” pure regions of parameter space give rather poor estimates for mχ < MW. We show that in the regions of parameter space favored by cosmology, the neutralino is a “nearly” pure bino state with mχ⪆ 100 GeV. The SUSY GUTs mass relations then imply m∼l ⪆ 200 GeV and mq,g ⪆ 600 GeV, all well within the reach of future hadron colliders.

CP violation via electroweak gauginos and the electric dipole moment of the electron.

The effective Lagrangian which exhibits explicitly the transmission of the CP-violating phases induced via the electroweak gaugino masses below the scale of the spontaneous breaking of SU(2${)}_{\mathit{L}}$\ifmmode\times\else\texttimes\fi{}${\mathrm{U}}_{\mathit{y}}$(1) electroweak gauge symmetry is deduced. The formalism is used to compute the one-loop electric dipole moment of the electron including the full set of neutralino states. Contributions of neutralinos other than the photino are found to be significant. It is shown that the current data excludes maximal CP violation in the electroweak sector except for selectron masses \ensuremath{\gtrsim}200 GeV and photino masses \ensuremath{\gtrsim}750 GeV.

A new aspect of the mass density of relic neutralinos

Abstract A cosmological constraint to the low energy minimal supersymmetric model, in which the lightest neutralino state is stable, is reconsidered. We show that the mass relation between squarks and sleptons imposed by the model can be essential in estimating the mass density of relic neutralinos. The mass relation leads to drastically different and smaller allowed regions of parameter space. If the lightest neutralino is gaugino-like and lighter than W, the condition Ω requires that the squark and gluino are nearly degenerate in mass.

Supersymmetry phenomenology and the nature of the lightest supersymmetric particle.

We show that in addition to the photinolike and Higgsino-like states usually considered as candidates for the lightest supersymmetric particle (LSP), there is yet one more state in the neutralino sector which could be the LSP in minimal supergravity models. In this paper, we study how the phenomenology of supersymmetry is altered depending on the nature of the LSP. Within the framework of minimal supergravity models, we demonstrate that if the mass of the LSP is small compared to that of the W boson, the lightest chargino and the next to lightest neutralino states are always lighter than ${M}_{W}$ and ${M}_{Z}$ independent of the soft-supersymmetry-breaking gaugino masses. We show that the W- and Z-boson decay widths into these particles depends quite significantly on the nature of the LSP. We further show that the bound on the scalar-electron mass of the ASP detector at the SLAC storage ring PEP is considerably weakened if the LSP is the new state discussed above, even if this state is dominantly a gaugino. Finally, we briefly study the phenomenology of the LSP in the context of superstring-inspired E(6) models.

Signals of supersymmetry at the Z 0 resonance

Abstract The Z0 boson can have a sizeable branching ratio into a pair of neutralinos (the fermionic superpartners of the neutral gauge and Higgs bosons). All the subsequent decays of the heavier neutralinos lead to very distinctive signatures in e+e− collisions at the Z0 pole. This may even be an efficient way to produce the Higgs boson. We study the various branching ratios as functions of the parameters of the underlying supersymmetric theory, making no ad hoc assumptions on the actual composition of the physical neutralino states.