Origin of exotic-quark masses

Establish a viable mechanism for generating masses for the exotic quarks in the nonstandard anomaly-free fermion solution while avoiding the strong Yukawa couplings and nondecoupling Higgs-coupling corrections associated with generating their masses through the Standard Model Higgs mechanism.

Background

The nonstandard anomaly-free solution contains an exotic colored weak-doublet quark and two colored singlet quarks with opposite hypercharges. In a direct Standard Model realization, gauge invariance permits Yukawa-generated exotic-quark masses through the Standard Model Higgs only for q = 1/2. TeV-scale masses then require Yukawa couplings of order six or larger, placing the theory in a strong-coupling regime, while the colored fermions also produce nondecoupling contributions to the Higgs decay channels h → gg and h → γγ.

The paper discusses possible ways around this difficulty, including adding opposite-chirality partners to form a vectorlike exotic sector and introducing a separate SU(2)L′ gauge group whose symmetry-breaking scale generates the exotic-quark masses. The authors nevertheless identify the general origin of the exotic-quark masses as unresolved and requiring further investigation.