3 v 3 9 J ul 1 99 7 RAL 97 - 007 SHEP 97 - 01 hep - ph / 9703293 String Unification , Spaghetti Diagrams and Infra - Red Fixed Points

ar X iv : h ep - p h / 97 07 46 2 v 1 2 5 Ju l 1 99 7 OUTP - 97 - 32 - P July 1997 Strong Unification

We investigate the possibility that unification occurs at strong coupling. We show that, despite the fact the couplings pass through a strong coupling regime, accurate predictions for their low energy values are possible because the couplings of the theory flow to infrared fixed points. We determine the low-energy QCD coupling in a favoured class of strong coupling models and find it is reduced...

String Unification , Spaghetti Diagrams and Infra - Red Fixed Points

We consider a scenario in which the minimal supersymmetric standard model (MSSM) is valid up to an energy scale of ∼ 10 16 GeV, but that above this scale the theory is supplemented by extra vector-like representations of the gauge group, plus a gauged U(1) X family symmetry. In our approach the extra heavy matter above the scale ∼ 10 16 GeV is used in two different ways: (1) to allow (two-loop)...

ep - p h / 98 08 42 9 v 3 2 2 Ja n 19 99 RAL - TR - 1998 - 037 DTP / 98 / 32 Cavendish - HEP - 97

SHEP 97 - 07 Infra - Red Stable Fixed Points of Yukawa Couplings in Supersymmetric Models

We provide the solutions of the fixed point conditions of the Yukawa sector for a large class of N = 1 supersymmetric theories including the minimal and next-to-minimal supersymmetric standard models and their grand unified and other extensions. We also introduce a test which can discriminate between infra-red stable, infra-red unstable and saddle point solutions, and illustrate our methods wit...

ar X iv : h ep - t h / 97 10 01 6 v 4 2 9 O ct 1 99 7 K 3 Surfaces , Igusa Cusp Form and String Theory

It has recently become apparent that the elliptic genera of K3 surfaces (and their symmetric products) are intimately related to the Igusa cusp form of weight ten. In this contribution, I survey this connection with an emphasis on string theoretic viewpoints.