Abstract
We present a stringy mechanism to generate Dirac neutrino masses by -instantons in an experimentally relevant mass scale without fine-tuning. Within type IIA string theory with intersecting -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 orientifold compactification, where perturbatively absent Dirac neutrino masses can be generated by -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 nonperturbative stringy effects.
- Received 2 April 2008
DOI:https://doi.org/10.1103/PhysRevD.78.066012
©2008 American Physical Society