Abstract
We consider the Yukawa couplings for quarks and leptons in the context of Pati–Salam model using intersecting D-brane models where the Yukawa coupling matrices are rank one in a simple choice of family replication. The CKM mixings can be explained by perturbing the rank 1 matrix using higher order terms involving new Higgs fields available in the model. We show that the near bi-large neutrino mixing angles can be naturally explained, choosing the light neutrino mass matrix to be type II seesaw dominant. The predicted value of Ue3 is in the range ≃0.05–0.15. In the quark sector, Vcb is naturally close to the strange/bottom quark mass ratio and we obtain an approximate relation VubVcb≃(ms/mb)2Vus. The geometrical interpretations of the neutrino mixings are also discussed.
Highlights
Understanding the masses and the mixings of quarks and leptons is one of the most important issues in particle physics
We have studied Yukawa coupling structures in the intersecting D-brane models with the Pati-Salam gauge symmetry with extra U(1) symmetries
In the quark sector, Vcb is naturally close to the strange/bottom quark mass ratio, and there exists a simple relation among the CKM mixing angles and a quark mass ratio
Summary
Understanding the masses and the mixings of quarks and leptons is one of the most important issues in particle physics. The N stack of D-branes can form U(N) gauge fields, and at the intersection between the N stack and M stack of D-branes, a massless chiral fermion belonging to (N, M ) bi-fundamental representation can appear Such a situation is very attractive to obtain quark and lepton fields in the standard model and in the models where the gauge group is given as direct group such as Pati-Salam model [10]. One interesting issue is that in the simple models, Yukawa matrices are written as factorized form yij = xLi xRj [11, 18] This originates from a geometrical reason that the left- and right-handed fermions are replicated at the intersecting points on the different tori, and the Yukawa couplings are given as an exponential form of sum of the triangle areas.
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