D-Instanton Generated Dirac Neutrino Masses

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 Z2 × 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 nonperturbative stringy effects. Disciplines Physical Sciences and Mathematics | Physics Comments Suggested Citation: M. Cvetič and P. Langacker. (2008). "D-instanton generated Dirac neutrino masses." Physical Review D. 78, 066012. © 2008 The American Physical Society http://dx.doi.org/10.1103/PhysRevD.78.066012 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/physics_papers/93 D-instanton generated Dirac neutrino masses Mirjam Cvetič* and Paul Langacker Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, USA Institute for Advanced Study, Princeton, New Jersey, USA (Received 2 April 2008; published 18 September 2008) 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 Z2 Z2 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 nonperturbative stringy effects. DOI: 10.1103/PhysRevD.78.066012 PACS numbers: 11.25.Wx, 14.60.Pq