Strong CP, Up-Quark Mass, and the Randall-Sundrum Microscope

Abstract
The fermion mass hierarchy can be obtained with O(1) parameters in the Randall-Sundrum (RS) model, via exponential bulk profiles. In particular, a tiny up quark mass m_u << MeV does not require a chiral symmetry or fine-tuning in this setup. Therefore, the RS model can provide a natural geometric resolution of the strong CP problem, while addressing the hierarchy and flavor puzzles. In simple realizations, this hypothesis can be tested at future colliders, like the LHC, by measuring the spectrum of level-1 Kaluza-Klein (KK) quarks. In this sense, these KK states act as a "microscope" for probing light fermion masses.

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