We consider the breaking of the grand unification group SO(10) to the standard model gauge group through several chains containing one intermediate breaking scale. Using the values of the gauge coupling constants at the scale M z derived from recent data from the CERN ef e-collider LEP, we determine the intermediate and the unification scales using two-loop renormalization group equations with appropriate matching conditions. Some chains are ruled out from experimental constraints. For the allowed ones, the intermediate scale is high, in the range of 1 0~-1 0~~ GeV. PACS number(s): 12.10.Dm, 12.15.C~ Recently it has been emphasized [I, 21 that the precision of data from the CERN e+e-collider LEP allows the extraction of the three coupling constants of the standard model very accurately, and this enables an extrapolation to high energies with very small errors. In these papers it was shown that if one extrapolates the couplings without change of particle content (i.e., with three families of fermions and one doublet of Higgs boson) or the group structure in the intervening energy scale, these couplings do not come together at a single point. Although this result is not unexpected, the statistical significance has been greatly improved. For example, LEP data imply [3] where cui = g:/4~, and gl, gz, 93 denote the normalized gauge coupling constants for the U(l)y, S U (~) L , and SU(3), factors, respectively. Now, if we take the central values for crl and a 2 , we need cr,(Mz) cz 0.07 in order to achieve unification. This is more than seven standard deviations removed from the mean value.In Refs.[I] and [2] it was further pointed out that the minimal supersymmetric model, with the supersymmetry-breaking scale MsusY N

We consider the breaking of the grand unification group SO(10) to the standard model gauge group through several chains containing two intermediate stages.Using the values of the gauge coupling constants at a scale M z derived from recent data from the CERN e+e-collider LEP, we determine the range of their intermediate and unification scales. In particular, we identify those chains that permit new gauge structure at relatively low energy (= 1 TeV). PACS number (s): 12.10.Dm, 12.15.Cc, 14.80.Er Recently, SO(10) [l] breaking chains with one intermediate stage [2] have been examined in light of the latest LEP data [3] from the CERN e+e-collider LEP. These data give 47 2892 -

We consider an arbitrary supersymmetric U͑1͒ gauge factor at the TeV scale, under which the two Higgs superfields H 1,2 of the standard model are nontrivial. We assume that there is a singlet superfield S such that H 1 H 2 S is an allowed term in the superpotential. We discuss first the generic consequences of this hypothesis on the structure of the two-doublet Higgs sector at the electroweak energy scale, as well as Z-ZЈ mixing and the neutralino sector. We then assume the existence of a grand unified symmetry and universal soft supersymmetry-breaking terms at that scale. We further assume that the additional U͑1͒ is broken radiatively via a superpotential term of the form hh c S, where h and h c are exotic color-triplet fields which appear in E 6 models. We show that the U͑1͒-breaking scale and the parameter tan␤ϵv 2 /v 1 are then both predicted as functions of the H 1 H 2 S coupling.

Contrary to commonly held belief, we show that one can obtain a low value for M#, the SU(2)H breaking scale, in grand unification theories based on SO(10). This possibility emerges in the supersymmetric version of SO(10) with a judicious choice of Higgs content. The unification scale is found to be consistent with the constraint from proton decay. This result is first explicitly demonstrated using the one-loop renormalization group equations, and then a full two-loop analysis is carried out.It is commonly believed [1,2] that the group SU(2).R has to be broken at a large energy scale MR ~ 10 10 GeV if it is to emerge from a grand unified symmetry such as SO(10). This is also assumed to be true for the supersymmetric (SUSY) version of SO( 10) [1,2]. Consequently, additional gauge bosons that could possibly be produced at supercollider energies are thought to originate only from additional U(l) factors which lead to Z' bosons [3]. The phenomenology of new charged W bosons at supercolliders is therefore less frequently investigated [4], We will show in this Letter that although the above result is true for the simplest Higgs structure, if this sector is suitably enlarged, the scale for the right-handed gauge bosons, MR, could be made arbitrarily low. We will consider only the supersymmetric version in detail, with some brief remarks on the nonsupersymmetric case given at the end of our discussion.We investigate the break chainwhere, as an example of our notation, 2^ represents SU(2)i,. Here, we have set the "effective" super symmetry breaking scale to be Mz, and will comment on this later. In Ref.[5], it was shown that if both 2JJ2R\B-L^C singlets of the 210 representation, together with the ^L^BXB-L&C singlet of the 45 representation, acquire vacuum expectation values (VEVs) then this is sufficient to break supersymmetric SO(10) down to supersymmetric 2L2RIB-L%C without D parity. The breaking at MR can be performed either by the Higgs fields in the 1260126 representation or in the 16 © 16 representation and we consider both these possibilities in our discussion below. We further assume that ordinary electroweak breaking at the Z scale is achieved as usual by a complex 10 representation. For the purpose of generating fermion masses, we assume that the entire bi-doublet of the 10 representation has a mass at the scale of Mz> [We remind the reader that a bi-doublet corresponds to the (2,2,0,1) representation of 2L2R1B-L^C] Also, we assume that the SU(2)# triplets of the 126 and 126 representations and the SU^)^ doublets of 16 and 16 representations have masses at the scale MR. All other Higgs multiplets are given masses of order MJJ as follows from the survival hypothesis. We make the important observation that in this symmetry breaking pattern pseudo Goldstone bosons do not appear [5].First let us examine the one-loop equations:The 6j's are the one-loop beta functions, which for the supersymmetric case are given byfor n g generations, the gauge group SU(iV), and the complex Higgs fields contribution which is parametri...

The totality of neutrino-oscillation phenomena appears to require the existence of a light singlet neutrino. As pointed out recently, this can be naturally accommodated with a specific extra U(1) factor contained in the superstring-inspired E 6 model and its implied particle spectrum. We analyze this model for other possible consequences. We discuss specifically the oblique corrections from Z-Z' mixing, the phenomenology of the two-Higgs-doublet sector and the associated neutralino sector, as well as possible scenarios of gauge-coupling unification.