Review of free-fermionic 4d string models

TL;DR

This paper reviews four-dimensional free-fermionic string models, focusing on their low-energy predictions, model building techniques, and implications for supersymmetry breaking and extra dimensions.

Contribution

It provides a comprehensive overview of free-fermionic string constructions and discusses their potential phenomenological implications and unique features.

Findings

Presence of fractional electric charge states

Calculation of string unification scale

Prediction of a large extra dimension at TeV scale

Abstract

I review the main properties of four-dimensional strings constructed with free-fermions on the world-sheet. In particular I discuss possible model independent low energy predictions related to the existence of states with fractional electric charges, the computation of the string unification scale, the string model building, and the perturbative approach to supersymmetry breaking which makes the spectacular prediction of a new large dimension at the TeV scale.