Diagonalizing the visible adjoint geometry
A basis discipline for spectra and mass terms.
Bosons
Which components look like gauge bosons after pullback
How to derive spacetime fields $X$ can actually see.
What the bosons are
In this instantiation, "bosons" are not extra fields on $X$; they are the ambient connection, curvature, and torsion data on $Y^{14}$, seen through restriction and pullback.