Conjugate boundary conditions, Kaluza-Klein fermions, and an extended seesaw model
- 1Kansai University
- 2Matsue College of Technology
- 3Okinawa College
Abstract
A bstract : In this paper, we discuss the conjugate boundary condition (CBC), which has recently been studied as a way of realizing a Majorana fermion within a compactified five-dimensional theory (ℳ ⁴ ⊗ S ¹ /Z ₂ ). The Majorana fermion which plays a crucial role in the seesaw scenario arises as a zero mode (lowest mode) by imposing the CBC. Although each nonzero Kaluza-Klein (KK) mode is also naively expected to be described by two Majorana fermions, we show by direct calculation that they can be combined into a Dirac spinor in the free theory or up to the level of the quadratic term in the Lagrangian. This difference comes from the fact that an accidental U(1) symmetry exists in the KK mode sector, though such a symmetry does not appear in the zero mode sector. We also point out that the compatibility between the CBC and the axial U(1) transformation plays a crucial role in the diagonalization of the KK mode.
We also investigate interactions compatible with both the CBC and the chiral orbifold projection. We find that a nontrivial bulk interaction between a CBC fermion and a chiral-orbifold fermion is allowed. As an application, we construct an extended seesaw scenario by utilizing both boundary conditions and such nontrivial bulk interactions. The resulting seesaw scenario has a different property in contrast with the conventional extended seesaw scenario; namely, the above new non-trivial interactions cause lepton number violation (LNV), while the Majorana mass term in our model does not violate lepton number.
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BibTeX
@article{abe2026conjugate,
title = {{Conjugate boundary conditions, Kaluza-Klein fermions, and an extended seesaw model}},
author = {Yugo Abe and Yuki Adachi and Yukihiro Fujimoto},
journal = {Journal of High Energy Physics},
year = {2026},
month = oct,
doi = {10.1007/jhep10(2026)094},
url = {https://link.springer.com/10.1007/JHEP10(2026)094},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Conjugate boundary conditions, Kaluza-Klein fermions, and an extended seesaw model
AU - Yugo Abe
AU - Yuki Adachi
AU - Yukihiro Fujimoto
PY - 2026
DA - 2026/10/08
JO - Journal of High Energy Physics
DO - 10.1007/jhep10(2026)094
UR - https://link.springer.com/10.1007/JHEP10(2026)094
AB - A bstract : In this paper, we discuss the conjugate boundary condition (CBC), which has recently been studied as a way of realizing a Majorana fermion within a compactified five-dimensional theory (ℳ ⁴ ⊗ S ¹ /Z ₂ ). The Majorana fermion which plays a crucial role in the seesaw scenario arises as a zero mode (lowest mode) by imposing the CBC. Although each nonzero Kaluza-Klein (KK) mode is also naively expected to be described by two Majorana fermions, we show by direct calculation that they can be combined into a Dirac spinor in the free theory or up to the level of the quadratic term in the Lagrangian. This difference comes from the fact that an accidental U(1) symmetry exists in the KK mode sector, though such a symmetry does not appear in the zero mode sector. We also point out that the compatibility between the CBC and the axial U(1) transformation plays a crucial role in the diagonalization of the KK mode. We also investigate interactions compatible with both the CBC and the chiral orbifold projection. We find that a nontrivial bulk interaction between a CBC fermion and a chiral-orbifold fermion is allowed. As an application, we construct an extended seesaw scenario by utilizing both boundary conditions and such nontrivial bulk interactions. The resulting seesaw scenario has a different property in contrast with the conventional extended seesaw scenario; namely, the above new non-trivial interactions cause lepton number violation (LNV), while the Majorana mass term in our model does not violate lepton number.
SN - 1029-8479
ER -