Abstract
Nontrivial strong dynamics often leads to the appearance of chiral composites. In phenomenological applications, these can either play the role of Standard Model particles or lift chiral exotics by partnering with them in mass terms. As a consequence, the RG flow may change the effective number of chiral generations, a phenomenon we call generation flow. We provide explicit constructions of globally consistent string models exhibiting generation flow. Since such constructions were misclassified in the traditional model searches, our results imply that more care than usually appreciated has to be taken when scanning string compactifications for realistic models.
Highlights
Infrared (IR) physics often differ considerably from the UV degrees of freedom
When a subgroup of such global symmetry is identified with a GUT or the SM gauge group, a new, composite, chiral generation may emerge in the IR or, alternatively, an existing chiral generation may become massive
In this approach, which we will refer to as the Nelson-Strassler (NS) mechanism, the RG flow leads to the appearance of light chiral composites in the IR increasing the effective number of chiral generations
Summary
For phenomenological purposes we are interested in gauging SU(6) global symmetry of the s-confining model discussed in the previous subsection (more precisely we are interested in gauging a subgroup of SU(6), such as a GUT SU(5) or the SM group SU(3)×SU(2)×U(1)) To this end, one must introduce a set of spectator fields charged under SU(6) but not SU(2)s (so that the s-confining dynamics remains unaffected) to ensure a cancellation of the cubic SU(6) anomaly. This is because SU(2)s is not yet confined in the UV and the matter fields transform in chiral representations of the full SU(6) × SU(2)s symmetry, while the representations of IR degrees of freedom are chiral under SU(6) In the latter case, the chiral properties of the model change as the theory flows from the UV to the IR. The existence of generation flow offers immense opportunities for model building both in field theory (section 3) and string theory (section 4)
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