# A kind of prediction from string phenomenology: extra matter at low energy

## TL;DR

This paper explores string-derived supersymmetric models predicting extra matter at low energies, aiming to reconcile unification scale discrepancies and analyze fermion mass patterns with potential flavor issues.

## Contribution

It demonstrates how orbifold heterotic string models can naturally include extra Higgses and vector-like triplets, addressing unification scale mismatch and fermion mass structures.

## Key findings

- Predicts three families of Higgses and vector-like triplets at low energies.
- Shows that viable models with controlled flavor-changing neutral currents exist.
- Provides a framework for understanding fermion masses and mixing angles in string-derived models.

## Abstract

We review the possibility that the Supersymmetric Standard Model arises from orbifold constructions of the E_8 x E_8 Heterotic Superstring, and the phenomenological properties that such a model should have. In particular, trying to solve the discrepancy between the unification scale predicted by the Heterotic Superstring (g_{GUT}x5.27x10^{17} GeV) and the value deduced from LEP experiments (2x10^{16} GeV), we will predict the presence at low energies of three families of Higgses and vector-like colour triplets. Our approach relies on the Fayet-Iliopoulos breaking, and this is also a crucial ingredient, together with having three Higgs families, to obtain in these models an interesting pattern of fermion masses and mixing angles at the renormalizable lebel. Namely, after the gauge breaking some physical particles appear combined with other states, and the Yukawa couplings are modified in a well controlled way. On the other hand, dangerous flavour-changing neutral currents may appear when fermions of a given charge receive their mass through couplings with several Higgs doublets. We will address this potential problem, finding that viable scenarios can be obtained for a reasonable light Higgs spectrum.