Inspired by the Standard Model of particle physics, we discuss a mechanism for constructing chiral, anomaly-free gauge theories. The gauge symmetries and particle content of such theories are identified using subgroups and complex representations of simple anomaly-free Lie groups, such as $SO(10)$ or $E_6$. We explore, using mostly $SO(10)$ and the $\mathbf{ 16}$ representation, several of these "imperfect copies" of the Standard Model, including $U(1)^N$ theories, $SU(5)\otimes U(1)$ theories, $SU(4)\otimes U(1)^2$ theories with 4-plets and 6-plets, and chiral $SU(3)\otimes SU(2)\otimes U(1)$. A few general properties of such theories are discussed, as well as how they might shed light on nonzero neutrino masses, the dark matter puzzle, and other phenomenologically relevant questions.
Categories: hep-ph