Deformed Intersecting D6-Brane GUTS II

Abstract

By employing D6-branes intersecting at angles in $D = 4$ type I strings, we construct {\em five stack} string GUT models (PS-II class), that contain at low energy {\em exactly the Standard model} with no extra matter and/or extra gauge group factors. These classes of models are based on the Pati-Salam (PS) gauge group $SU(4)_C \times SU(2)_L \times SU(2)_R$. They represent deformations around the quark and lepton basic intersection number structure. The models possess the same phenomenological characteristics of some recently discussed examples (PS-A and PS-I class) of four stack PS GUTS. Namely, there are no colour triplet couplings to mediate proton decay and proton is stable as baryon number is a gauged symmetry. Neutrinos get masses of the correct sizes. Also the mass relation $m_e = m_d$ at the GUT scale is recovered. The conditions for the non-anomalous U(1)'s to survive massless the Green-Schwarz mechanism are equivalent, to the conditions, coming from the presence of N=1 supersymmetry, in sectors involving the presence of {\em extra} branes and also required to guarantee the existence of the Majorana mass term for the right handed neutrinos. These conditions are independent from the number of {\em extra} U(1) branes. We also discuss the relative size of the leading worldsheet instanton correction to the trilinear Yukawa couplings in a general GUT model.