arXiv subjects

Wen-Xuan Ma

Publications and source records attributed to Wen-Xuan Ma.

4 recordsLinked to original sources

arXiv2026

Fermionic Kaluza-Klein mode mixing in braneworlds

We investigate fermionic Kaluza-Klein (KK) mode mixing in thick braneworld models subjected to generic background perturbations. Conventionally, isolated static backgrounds are completely described by a Schroedinger-like formulation, which yields an unperturbed orthogonal basis of KK eigenstates. However, generic perturbations possess a non-trivial spatial profile along the extra dimension. When the full interacting Dirac operator is expanded in this original basis, the spatial variation inevitably yields non-vanishing overlap integrals between distinct KK levels, thereby inducing off-diagonal couplings in the 4D effective mass matrix. Consequently, the original eigenstates are no longer exact physical eigenmodes of the perturbed system. To rigorously preserve the underlying 5D chiral structure and resolve the true physical states, we employ an exact Singular Value Decomposition (SVD) of the full, off-diagonal Dirac mass matrix. Our exact analysis reveals that this mode mixing introduces small but highly structured corrections to the mass eigenvalues. Specifically, parity-odd perturbation operators strictly induce same-parity mixing that preserves the macroscopic Z2 spatial symmetry, whereas parity-even operators trigger cross-parity mixing that shatters the Z2 symmetry, resulting in severe spatial polarization of the KK probability densities. Phenomenologically, such polarization shifts the wave functions toward the brane, turning probability zeros into non-zero values, which directly illuminates previously "dark" KK modes.

hep-th↗

arXiv2026

Interactions between different Kaluza-Klein modes in brane world

In brane-world theory, through Kaluza-Klein (KK) reduction, a higher-dimensional U(1) gauge field manifests on the brane as a series of vector and scalar KK modes, while a bulk fermion field manifests as left- and right-handed components. However, these conclusions rely on the common assumption that there is no interaction between different levels of KK modes. Recent experimental phenomena, such as flavor mixing in particles, suggest that such interactions should be taken into account. To address this, we propose an \emph{Orthonormal Completeness Hypothesis} (OCH) for the basis functions used to expand the higher-dimensional field. By applying the OCH, we demonstrate that the effective action of a free bulk U(1) gauge field is intrinsically gauge-invariant in brane models with codimension-$d$ ($d \geq 1$). This effective action suggests the existence of interactions between different levels of KK modes, which can only be eliminated by choosing specific basis functions, provided the warp factors satisfy special commutation relations. In general, such interactions are universally present. We show the numerical calculations for these coupling coefficients in an interesting 6D brane world. This method can be extended to fermion fields, and it is shown that interactions between different levels of left- and right-handed KK modes exist, providing new insights into phenomena such as flavor mixing.

hep-th↗

arXiv2026

Kaluza-Klein mode mixing in braneworlds: constraints on scalar absorption and physical degrees of freedom

We investigate the mixing between Kaluza-Klein (KK) modes for a bulk U(1) gauge field within braneworld models. By demanding orthonormality and completeness for the KK basis functions, we demonstrate that the decoupling of mixed sectors, specifically of the vector-scalar and scalar-scalar types, imposes stringent constraints on the warp factors of codimension-d (d>1) backgrounds. We show that the gauge invariance of the four-dimensional effective action is preserved despite such mixing, manifesting as an intrinsic property of the massive vector KK sector. However, the generic presence of vector-scalar mixing fundamentally alters the absorption mechanism of the scalar modes, dynamically shifting the physical masses of the vector KK modes away from their unperturbed eigenvalues. In (4+2)-dimensional models, the existence of two distinct scalar sectors significantly enriches the mixing dynamics. As the massive vectors absorb only specific linear combinations of these scalars, a residual set of massive scalar KK modes persists as physical degrees of freedom.

hep-th↗

arXiv2026

Massive $U(1)$ gauge field and their accompanying scalars in brane world

In brane-world scenarios, the effective action of a massless bulk $U(1)$ gauge field preserves gauge invariance via couplings between massive vector Kaluza-Klein (KK) modes and scalar KK modes. In this work, we extend this framework by introducing a term $(\nabla^M X_M)^2$ into the massless bulk $U(1)$ gauge action. This modification explicitly breaks the full gauge redundancy while preserving a residual gauge symmetry both in the bulk and on the brane. In this setup, the scalar KK modes can acquire masses from the background geometry. Notably, we find that on the 5D brane, these scalar KK modes are lighter than the vector KK modes. In contrast, on the 6D brane, two types of scalar modes emerge; the mixed interactions between them give rise to oscillations among these scalar modes.

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