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

Abstract

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 investigating whether this structure can also arise from a D-brane mechanism. We investigate a local Type IIB D3${}_{+}$--D7--D3${}_{-}$/E3 mechanism for generating perturbatively forbidden interbrane mixing. Under explicitly stated microscopic conditions, the E3 instanton generates fermion mixing with both scalar and pseudoscalar components. The pseudoscalar component reproduces the characteristic mixing structure of the two-sheeted fermion operator, while D7 Wilson transport supplies the gauge-invariant relative connection between the two brane sectors. We establish the corresponding gauge matching for transitions between stationary states at resonance. The analysis also provides a model-building roadmap toward a compact phenomenological realization. Such a realization requires electromagnetic sequestering of the two fermion sectors and a sufficiently light non-uniform D7 gauge mode capable of mediating a long-range relative interaction. In such a compactification, the mixing parameter $g$ would be determined by microscopic instanton data and matter-field normalization, providing a connection to low-energy constraints.

arXiv comment27 pages, 2 figures, Expanded analysis of E3-instanton charged zero modes, including an explicit orbifold example and RR charge cancellation. Clarified gauge-matching conditions and the limitations of the local construction