Realistic Yukawa Structures from Orientifold Compactifications
Mirjam Cvetič, James Halverson, Robert Richter
TL;DR
The paper systematically evaluates globally consistent MSSM D-brane quivers from three- and four-stack constructions, focusing on how perturbatively forbidden Yukawas can be generated by D-brane instantons while avoiding unwanted terms. It develops and applies top-down (tadpole and massless hypercharge) and bottom-up (spectrum, Yukawas, neutrino masses) constraints, revealing that only a small subset of quivers meet all phenomenological requirements. The analysis distinguishes several hypercharge embeddings and realizes that many instanton-induced couplings either fail to produce realistic mass textures or induce R-parity violation or large mu-terms. It also shows that neutrino masses can be accommodated either via a seesaw mechanism with Majorana masses generated non-perturbatively or through highly suppressed Dirac masses, depending on the quiver, with several viable examples identified, especially in the four-stack and Sp(2) realizations. Overall, the work provides a focused map of MSSM quivers with realistic Yukawa structures that can guide future explicit string model-building efforts.
Abstract
We perform a systematic analysis of globally consistent D-brane quivers which realize the MSSM, and analyze them with respect to their Yukawa couplings. Often, desired couplings are perturbatively forbidden due to the presence of global U(1) symmetries. We investigate the conditions under which D-brane instantons will induce these missing couplings without generating other phenomenological drawbacks, such as R-parity violating couplings or a mu-term which is too large. Furthermore, we systematically analyze which quivers allow for a mechanism that can account for the small neutrino masses and other experimentally observed hierarchies. We show that only a small fraction of the globally consistent D-brane quivers exhibits phenomenology compatible with experimental observations.