Branes and Orbifolds are Opaque

TL;DR

The paper shows that gauge fields in extra dimensions inevitably acquire brane-localized kinetic terms via radiative corrections, leading to logarithmic divergences that render these terms independent input parameters in the effective theory. In five dimensions, these brane terms significantly distort the Kaluza-Klein spectrum and the couplings of KK modes to brane and bulk matter, with striking effects such as a light collective mode and suppressed couplings of heavy KK states to brane fields. The authors develop a detailed KK decomposition in scenarios with one or two opaque branes, including symmetric and asymmetric configurations, and analyze the resulting phenomenology, including implications for collider bounds and flavor physics in split-fermion models. Overall, the work demonstrates that brane/boundary terms are a crucial, non-predictable ingredient in bulk gauge theories with extra dimensions, capable of qualitatively altering experimental signatures and model-building possibilities.

Abstract

We examine localized kinetic terms for gauge fields which can propagate into compact extra dimensions. We find that such terms are generated by radiative corrections in both theories with matter fields confined to branes and in theories imposing orbifold boundary conditions on bulk matter. In both cases, the radiative corrections are logarithmically divergent, indicating that from an effective field theory point of view they cannot be predicted in terms of other parameters, and should be treated as independent leading order parameters of the theory. Specializing to the five dimensional case, we show that these terms may result in gross distortions of the Kaluza-Klein gauge field masses, wave functions, and couplings to brane and bulk matter. The resulting phenomenological implications are discussed.

Figures (8)

• Figure 1: Graphical solution of the eigenmass equation, $-\tan[\pi m R] = (r_c / 2 R) \times m R$ for several values of $r_c / R$.
• Figure 2: The $n=1,2,3,4$ (bottom to top) KK mode masses in units of $1/R$ and couplings relative to the zero mode coupling for the one-brane case, as a function of $r_c / R$.
• Figure 3: The $n=1$ and $n=2$ KK mode wave functions for one brane with $r_c/R=0, 1, 2,$ and $4$.
• Figure 4: The $n=1,2,3,4$ (bottom to top) KK mode masses in units of $1/R$ and KK mode couplings relative to the zero mode coupling as a function of $r_c / R$ for two branes with equal terms.
• Figure 5: The $n=1$ and $n=2$ KK mode wave functions for two branes with equal $r_1/R=0, 1, 2,$ and $4$.