D-Instanton Generated Dirac Neutrino Masses

TL;DR

This paper proposes a string theory-based mechanism using D-instantons to generate small Dirac neutrino masses in line with experimental observations, avoiding fine-tuning and Majorana masses.

Contribution

It introduces a specific stringy framework within Type IIA intersecting D-branes that naturally produces Dirac neutrino masses via D-instantons, absent in perturbation theory.

Findings

D-instantons can generate Dirac neutrino masses in the observed range

Majorana neutrino masses remain perturbatively absent

Provides a string-theoretic explanation for small neutrino masses

Abstract

We present a stringy mechanism to generate Dirac neutrino masses by D-instantons in an experimentally relevant mass scale without fine-tuning. Within Type IIA string theory with intersecting D6-branes, we spell out specific conditions for the emergence of such couplings and provide a class of supersymmetric local SU(5) Grand Unified models, based on the Z_2 x Z'_2 orientifold compactification, where perturbatively absent Dirac neutrino masses can be generated by D2-brane instantons in the experimentally observed mass regime, while Majorana masses remain absent, thus providing an intriguing mechanism for the origin of small neutrino masses due to non-perturbative stringy effects.