What if the masses of the first two quark families are not generated by the standard model Higgs boson?

Abstract

We point out that in the standard model there is meaningful quark mixing even in the extreme chiral (EC) limit, where only the third generation of quarks acquires mass. This mixing is in general expected to be of order 1 and the fact that jV 13 j 2 þ jV 23 j 2 ≈ 1.6 × 10 −3 implies a novel fine-tuning problem in the SM which we point out for the first time. We propose a possible way of avoiding this fine-tuning by introducing a symmetry S which leads to V CKM ¼ 1, with only the third generation of quarks acquiring mass. We consider two scenarios for generating the mass of the first two quark generations and full quark mixing based on the assumption that the masses of the first two quark families are not generated by the standard Higgs. One consists of the introduction of a second Higgs doublet which is neutral under S. The second scenario consists of assuming new physics at a high energy scale, contributing to the masses of light quark generations, in an effective field theory approach. This last scenario leads to couplings of the Higgs particle to ss and cc which are significantly enhanced with respect to those of the SM. In both schemes, one has scalar-mediated flavor-changing neutral currents which are naturally suppressed. Flavor-violating top decays are predicted in the second scenario at the level Brðt → hcÞ ≥ 5 × 10 −5 .

Self-consistent Dark Matter simplified models with an s-channel scalar mediator

“…Moreover, in [91] there is a claim of the presence of fine-tuning in the CKM matrix, given the smallness of |V 13 | 2 + |V 23 | 2 . This framework complied with one of the possible explanations of this alignment present in the CKM matrix proposed in [91] -however the magnitude of FCNC both at tree and loop level of this model should be analysed and may provide additional constrains on the allowed values of . The BGL model induces such FCNC at tree level with couplings for the second doublet given by 16 the off-diagonal elements of…”

Higgs bosons with large couplings to light quarks

“…• Flavorful 2HDMs [136][137][138][139][140][141][142]: there are also models in the literature where the SM-like…”

Rare top decays as probes of flavorful Higgs bosons

“…The SM flavor puzzle can be partially addressed by introducing an additional source of EWSB that is responsible for generating mass for the first and second generation fermions, as proposed in [18] (see also [19][20][21][22]). Arguably the simplest realization of this scenario is a Two Higgs Doublet Model (2HDM), in which one Higgs doublet (approximately identified as the 125 GeV Higgs boson) couples mainly to the third generation, while the second Higgs doublet couples mainly to the first and second generations.…”