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arXiv · 2603.09656

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

Wen-Xuan Ma·Chun-E Fu
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Abstract

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.

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Wen-Xuan Ma, Chun-E Fu. 2026-03-10. Kaluza-Klein mode mixing in braneworlds: constraints on scalar absorption and physical degrees of freedom. https://arxiv.org/abs/2603.09656

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