Phenomenological Aspects of Supersymmetric Standard Models without Grand Unification

When the GUT relation on gaugino masses is relaxed, the mass and composition of the lightest neutralino are different from those in the GUT case. We discuss its phenomenological implications on the relic abundance of the neutralinos and on superparticle searches. In particular, we focus on the case where the neutral component of Winos dominates the lightest neutralino. It turns out the Wino-LSP is not a candidate for the dark matter. Address after September 1, 1992: TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., V6T 2A3, Canada In supersymmetric (SUSY) SU(5) grand-unified theories [1] and many other SUSY GUTs, a one-loop renormalization group (RG) [2] analysis gives us the following relation for the gaugino mass parameters M1 : M2 : M3 = 5/3g 2 1 : g 2 2 : g 2 3 ≃ 1 : 2 : 7, (1) where gi (i =1, 2, 3) are the gauge coupling constants of the gauge groups U(1)Y , SU(2)L and SU(3)C , respectively, andMi (i =1, 2, 3) the corresponding gaugino mass parameters. Note that this relation holds, independent of the particle content between the electroweak scale and the GUT scale. Therefore, eq. (1) provides an important test of the idea of the GUTs. There are, however, many well-motivated models in which the relation (1) is not satisfied. Examples include SU(3)C × SU(2)L × U(1)Y string models [3] and a flipped SU(5) model [4] whose gauge structure is SU(5)× U(1)X . In the former, M1, M2 and M3 are unknown parameters which will be determined by string dynamics, whereas in the latter, M1 is independent of the others. Indeed in the flipped SU(5) it has been argued [5] that, using a RG analysis, |M1| ≫ |M2| is favored to achieve the correct gauge symmetry breaking SU(5)×U(1)X → SU(3)C ×SU(2)L×U(1)Y → SU(3)C ×U(1)em. In this paper, we will consider phenomenological aspects of SUSY standard models without the GUT relation (1) which is assumed in most of the literature (see however refs. [6, 7, 8]). In particular, we are concerned with the mass ratio r ≡ M1/M2, since it is an important parameter in the neutralino mass matrix as we will explain later. We assume, as usual, that the lightest neutralino is also the lightest superparticle (LSP). To clarify its properties is thus important in SUSY phenomenology from the viewpoints of both accelerator physics and cosmology, especially when the LSP is stable due to a Z2 symmetry called R-parity. In this paper we will mainly discuss the case