Majorana neutrino masses by D-brane instanton effects in magnetized orbifold models

Abstract

We study Majorana neutrino masses induced by D-brane instanton effects in magnetized orbifold models. We classify possible cases, where neutrino masses can be induced. Three and four generations are favored in order to generate neutrino masses by D-brane instantons. Explicit mass matrices have specific features. Their diagonalizing matrices correspond to the bimaximal mixing matrix in the case with even magnetic fluxes, independently of the modulus value τ . On the other hand, for odd magnetic fluxes, diagonalizing matrices correspond nearly to the tri-bimaximal mixing matrix near τ = i, while they become the bimaximal mixing matrix for larger Imτ . For even fluxes, neutrino masses are modular forms of the weight 1 on T 2 /Z 2 , and they have symmetries such as S 4 and ∆ (96) × Z 3 .

On Stringy Origin of Minimal Flavor Violation

“…where h i denote the conformal dimensions of vertex operators V i , corresponding to massless modes. Here, we rely on the perturbative calculation for n-point couplings, but non-perturbative effects such as D-brane instanton effects in Type IIA string theory lead to a similar structure of n-point couplings [8] protected by non-anomalous symmetries [9], where the coefficient includes the instanton action factor e −Sinstanton . The explicit forms of n-point couplings are known on toroidal backgrounds, but it is challenging to derive npoint couplings on more general backgrounds such as Calabi-Yau threefolds.…”

Yukawa textures in modular symmetric vacuum of magnetized orbifold models

“…The charged lepton masses are given by Dirac mass matrix as the quarks, but we need to study Majorana masses for the neutrino sector. For example, in [88], Majorana masses for right-handed neutrino induced by non-perturbative effects of D-brane instanton effects were studied systematically in magnetized orbifold models. We would also study it and examine the realization of both quark and lepton flavors elsewhere.…”

Modular symmetry anomaly and non-perturbative neutrino mass terms in magnetized orbifold models

“…Next, let us review the flavor structure of the Majorana neutrino masses generated by D-brane instanton effects in the magnetized orbifold models [57]. The D-brane instanton is an instantonlike solution of string theory.…”

“…Actually, from such compactifications, realistic quark masses and mixing angles as well as charged lepton masses have been studied [49][50][51][52]. In D-brane models, D-brane instanton effects induce new terms such as righthanded Majorana neutrino mass terms [53][54][55], and explicit forms were also studied in magnetized models [56,57]. We study the modular symmetry anomaly and breaking symmetries due to neutrino mass terms induced by D-brane instanton effects.…”