Construction of Realistic Standard--like Models in the Free Fermionic Superstring Formulation

TL;DR

This paper constructs realistic superstring models in the free fermionic formulation, achieving three generations, suppressed proton decay, and realistic mass hierarchies, with specific gauge and matter content.

Contribution

It introduces a restricted class of free fermionic superstring models with realistic features, including three generations, suppressed proton decay, and hierarchical fermion masses.

Findings

Models have exactly three chiral generations.

Proton decay operators are suppressed by gauged U(1) symmetries.

The models naturally explain the top-bottom mass hierarchy.

Abstract

I discuss in detail the construction of realistic superstring standard--like models in the four dimensional free fermionic formulation. The analysis results in a restricted class of models with unique characteristics: (i) Three and only three generations of chiral fermions with their superpartners and the correct Standard Model quantum numbers. (ii) Proton decay from dimension four and dimension five operators is suppressed due to gauged $U(1)$ symmetries. (iii) There exist Higgs doublets from two distinct sectors, which can generate realistic symmetry breaking. (iv) These models explain the top--bottom mass hierarchy. At the trilinear level of the superpotential only the top quark gets a non vanishing mass term. The bottom quark and the lighter quarks and leptons get their mass terms from non renormalizable terms. This result is correlated with the requirement of a supersymmetric vacuum at the Planck scale. (v) The models predict the existence of small hidden gauge groups, like $SU(3)$, with matter spectrum in vector representations.