121161161
String model building in the free fermionic formulation
Abstract We consider the rules for string model building in the free fermionic formalism. Valid spin-structures on the string world-sheet correspond to automorphisms of the Lie algebra of the world-sheet supercharge. After reviewing and clarifying the model building rules we classify all such automorphisms. We then classify the mutually commuting sets of such automorphisms that are needed for model building. Finally we show how to construct all models with N = 4, N = 2, or N = 1 space-time supersymmetry. In four dimensional models, N = 1 space-time supersymmetry can only be achieved if the Lie algebra of the world-sheet supercharge is SU(2) 6 .
121122277
Fermion masses and phenomenology in SO(10) or SU(5) superstring compactifications
Abstract Symmetry breaking patterns and phenomenology of the SO(10) and SU(5) compactifications of the E 8 ×E 8 ′ heterotic superstring recently proposed by Witten are examined with regard to the fermion mass matrix. Under some circumstances there exist constraints due to the presence of relatively light charged leptons.
85558805
Cosmological constraints on heavy weakly interacting fermions
Abstract The masses and lifetimes of very heavy weakly interacting fermions which appear in many grand unified gauge models are constrained by the requirement that their decays in the hot big bang early universe should not generate excessive entropy which would dilute n B / n γ below its observed value.
118268870
Some Topics in Grand Unified Models and the Cosmological Baryon Asymmetry
In part I of this thesis some of the parameters relevant to the production of a cosmological baryon number asymmetry are considered in the context of grand unified models. General expressions for the average baryon number generated in the free decays of bosons are derived . The CP violation necessary for the generation of a baryon excess is discussed for a variety of SU(5) models. The kinematics of baryon number production in an illustrative SO(10) model is discussed in detail. In part II a viable SO(10) model is constructed which reproduces the phenomenological fermion mass and mixing angle values. A detailed discussion of the beta function for this model is presented. This analysis includes the effects of scalars.
120353647
Can the family group be a global symmetry
Abstract We consider the possibility that the family group may be a spontaneously broken continuous global symmetry. In the context of grand unification, the couplings of the associated Goldstone bosons to fermions can be sufficiently suppressed so as to satisfy the phenomenological bounds. For a maximal family symmetry this requires a large number of Higgs fields.
120861006
PECCEI-QUINN SYMMETRIES WITHOUT DOMAINS
In general, the unbroken discrete subgroup of a Peccei-Quinn symmetry gives rise to a domain problem: the formation of unacceptable domain walls in the course of the evolution of the early universe. In this paper, we construct an SU(5) model in which the unbroken discrete subgroup of a Peccei-Quinn symmetry is a trivial Z/sub 1/. That means that there is no domain problem for this model. It is pointed out that in models with more than one global U(1) symmetry it is easy to achieve a solution to the domain problem.
118943918
Real-Time Detection of Gravitational Microlensing
Real-time detection of microlensing has moved from proof of concept in 1994 (Udalski et al. 1994a, Alcock et al.1994) to a steady stream of events this year. Global dissemination of these events by the MACHO and OGLE collaborations has made possible intensive photometric and spectroscopic follow up from widely dispersed sites confirming the microlensing hypothesis (Benetti 1995). Improved photometry and increased temporal resolution from follow up observations greatly increases the possibility of detecting deviations from the standard point-source, point-lens, inertial motion microlensing model. These deviations are crucial in understanding individual lensing systems by breaking the degeneracy between lens mass, position and velocity. We report here on GMAN (Global Microlensing Alert Network), the coordinated follow up of MACHO alerts.