Grand Unification with Intermediate Scale Gauge Symmetries
Abstract
Using the values of the gauge coupling constants at the scale M_{Z} derived from recent data from the CERN e^+e^ - collider LEP, we consider the breaking of the non-supersymmetric grand unification group SO(10) to the standard model gauge group through several chains. Some chains are ruled out from experimental constraints. We determine the intermediate and unification scales for chains containing one intermediate breaking scale by use of two -loop renormalization group equations with appropriate matching conditions. For the allowed chains, the intermediate scale is high, in the range of 10^9-10 ^{11} GeV. We also determine the range of intermediate and unification scales for chains containing two intermediate stages. We identify chains where new chargeless gauge bosons are possible at relatively low energy ({~}1 TeV), but as expected find none where extra light charged gauge bosons can occur. However in a supersymmetric version of SO(10) with a judicious choice of Higgs content, we find that, contrary to commonly held belief, the SU(2) _{R} breaking scale can be low and hence new charged bosons may be within the reach of existing or future colliders. We also look at an example of a larger group, SU(16), that provides the possibility for a rich low energy gauge structure. In addition, we investigate the status of predictive fermion mass ansatze which make use of the grand unification scale conditions m_{e} = m_ {d}/3, m_mu = 3m_{s }, and | V_{cb }| = sqrt{m_{c}/m _{t}} in non-supersymmetric SO(10) grand unification. The gauge symmetry below an intermediate symmetry breaking scale M_ {I} is assumed to be that of the standard model with either one Higgs doublet or two Higgs doublets. We find in both cases that a maximum of four standard model parameters may be predicted within 1sigma experimental ranges in addition to predicting the top mass. We also discuss the possibility of third generation Yukawa coupling unification in the two Higgs standard model which leads to a greater predictive ability but also requires a large top quark mass (>180 GeV) and constrains alpha_{3c}(M_{Z }) to be near its lower 1sigma bound.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......108K
- Keywords:
-
- BOSONS;
- QUARK;
- Physics: Elementary Particles and High Energy