Abstract
We argue that extensions of the SM with a warped extra dimension, together with a new {mathbb {Z}}_2-odd scalar singlet, provide a natural explanation not only for the hierarchy problem but also for the nature of fermion bulk masses and the observed dark matter relic abundance. In particular, the Kaluza-Klein excitations of the new scalar particle, which is required to naturally obtain fermion bulk masses through Yukawa-like interactions, can be the leading portal to any fermion propagating into the bulk of the extra dimension and playing the role of dark matter. Moreover, such scalar excitations will necessarily mix with the Higgs boson, leading to modifications of the Higgs couplings and branching ratios, and allowing the Higgs to mediate the coannihilation of the fermionic dark matter. We study these effects and explore the viability of fermionic dark matter in the presence of these new heavy scalar mediators both in the usual freeze-out scenario and in the case where the freeze-out happens during an early period of matter domination.
Highlights
Fermion masses in warped extra dimension (WED) compactified on a S1/Z2 orbifold need to have a dynamical origin, since the fivedimensional (5D) bulk masses must be Z2-odd functions on the orbifold [8,9]
We argue that extensions of the Standard Model (SM) with a warped extra dimension, together with a new Z2-odd scalar singlet, provide a natural explanation for the hierarchy problem and for the nature of fermion bulk masses and the observed dark matter relic abundance
We have demonstrated that the addition of a Z2-odd scalar field developing a vacuum expectation value (VEV) in extra-dimensional models can account for the origin of the 5D fermion masses, and provide a unique window into any 5D fermionic dark sector
Summary
Fermion masses in WED compactified on a S1/Z2 orbifold need to have a dynamical origin, since the fivedimensional (5D) bulk masses must be Z2-odd functions on the orbifold [8,9]. The most natural solution to this problem is to dynamically generate these masses with the help of a Z2-odd bulk scalar field. If such scalar field develops a vacuum expectation value (VEV) with a non-trivial profile along the extra dimension, fermion bulk masses can arise dynamically through Yukawa-like interactions. We have explored this possibility in detail in [10], studying in particular its phenomenological consequences. In the more general case of a Higgs boson in the bulk of the extra
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