Seesaw Neutrinos from the Heterotic String

TL;DR

It is argued that this situation is quite common in heterotic orbifolds, where no large GUT representations are needed to generate the Majorana mass terms and the total number of right-handed neutrinos can be very large, up to O(100).

Abstract

We study the possibility of realizing the neutrino seesaw mechanism in the E8XE8 heterotic string. In particular, we consider its Z_6 orbifold compactifications leading to the supersymmetric standard model gauge group and matter content. We find that these models possess all the necessary ingredients for the seesaw mechanism, including the required Dirac Yukawa couplings and large Majorana mass terms. We argue that this situation is quite common in heterotic orbifolds. In contrast to the conventional seesaw of grand unified theories (GUTs), no large GUT representations are needed to generate the Majorana mass terms. The total number of right--handed neutrinos can be very large, up to O(100).

Figures (1)

• Figure 1: Couplings involving fields localized at different fixed points in 10D preserve the symmetry corresponding to the intersection of the local gauge groups $G_i$.