Matter Swapping between Two Branes: A Local Type IIB D3-D7-D3 Realization of Charged-Fermion Mixing via E3 Instantons

RESUMO

Effective infrared two-sheeted descriptions of fermion mixing between braneworlds have emerged in several distinct realizations and lead to testable matter-swapping effects, motivating low-energy searches and cosmological applications. The recurrence of the same low-energy fermion operator motivates asking whether this structure can also arise from a D-brane mechanism. We construct a local Type IIB D3$_+$-D7-D3$_-$/E3 realization in which direct interbrane mixing is perturbatively forbidden but generated non-perturbatively by a suitable E3 instanton sector. The resulting low-energy interaction reproduces the characteristic pseudoscalar structure of the two-sheeted fermion operator, together with its scalar companion, while D7 Wilson transport provides the required gauge-invariant relative connection. The construction therefore provides a local string realization of the same operator structure, subject to the stated instanton and zero-mode conditions. The analysis further provides a concrete model-building roadmap toward a compact phenomenological realization: the compactification must achieve electromagnetic sequestering of the two fermion sectors and support a sufficiently light non-uniform D7 gauge mode capable of mediating a long-range relative interaction. In such a complete compactification, the mixing parameter $g$ would in principle become computable from microscopic string data and directly testable against low-energy constraints.