
In the Selection–Stitch Model (SSM), the vacuum is a face-centered-cubic (FCC) lattice. It
grows by in-plane stitches and rare out-of-plane lifts [10], it carries a stabilizer code [11], and it
holds matter as nodes trapped in tetrahedral voids [10, 12]. A recent paper [13] showed that the
two orientations of these voids cannot be told apart in the static crystal, but become a real label
on the path of a moving defect. Giving each matter weight of the vacuum’s f
4
two copies, one per
orientation, gives the root system of E
6
. The orientation flip F reverses the label and folds e
6
back
to f
4
. It fixes one su(3), taken as color, and swaps the other two. Three conditions pick out a
charge Q, and on the 27 it gives the Standard Model charges [13].
That paper ended with one open question, the chiral projection. Its comparison with one Stan-
dard Model generation listed the weak doublets as “absent (kinematic home only)” and hypercharge
as “kinematic: Y = Q−T
3L
awaits the chiral projection” [13]. This paper takes up that question in
two parts. What exactly must be chosen to place the weak su(2) and fix hypercharge? And what
in the model makes the choice?
Main results. The logic runs in one direction. The earlier paper fixes Q [13]. This paper
classifies where the weak su(2) can sit, and the chosen place then fixes Y . (i) Of the twelve roots of
e
6
that commute with color, exactly four raise Q by one unit, two in each of the swapped factors.
If the weak su(2) is generated by a root, a hypercharge Y = Q −T
3
that commutes with color and
with the weak su(2) can be built in only two ways, up to a Weyl relabeling (Theorem 1). (ii) The
choice in the factor that acts on the charge-
2
3
quarks gives the hypercharges of one Standard Model
generation, plus the usual E
6
extra states, with no free parameter. The anomalies of the 27 cancel
(Theorem 2 and Proposition 1). (iii) The flip swaps the two choices and maps the weights of the
27 onto those of the 27. The choice is one bit, and the static crystal, which is symmetric under the
flip, cannot set it (Theorem 3 and Section 5). A hop of a defect applies the flip. On the quarks and
the charged lepton it reproduces the charge differences of a Dirac mass term (Proposition 2). (iv)
Reversing the direction in which the lattice grew acts on the roots exactly as the flip (Theorem 4).
This is a statement of covariance. It says which placement goes with which growth direction. It
becomes a selection mechanism only if the growth direction leaves a lasting physical record that
couples to the weak sector, and that is open (Section 6).
What is standard and what is new. Trinification, the 27 of E
6
, its hypercharges, its
anomaly freedom, and its left–right partners are standard parts of unified model building [6, 14, 15].
They are not claimed as new. What is new is how they arise here. The swapped factors come from
the up and down orientations of tetrahedral voids. The charge comes from the earlier construction,
and the choice between the factors is tied to the flip of those orientations and to the growth direction
of the lattice.
Scope. The results are statements about root systems, one representation, and a lattice ge-
ometry. No gauge dynamics is built. The paper does not explain why the charged bosons of the
unused factor are heavy or what supplies the Higgs quantum numbers. It does not show that void
orientation is Lorentz chirality, and it does not build the left-handed charged-current coupling of
the Standard Model. Physical names are labels for algebraic objects, as in Ref. [13]. Each claim
is marked derived (proved), computed (evaluated by the script), argued, or open. A public script
checks every computed claim (see Data Availability).
2 The Construction Used
This section lists, with explicit vectors, everything taken from Ref. [13]. The 72 roots live in
R
4
bond
⊕ R
2
class
. The 24 roots ±e
i
± e
j
of D
4
are the vacuum bonds. Each of the 24 short matter
weights s of f
4
is lifted twice, to (s, ϵ v
[s]
) with ϵ = ±1. Here v
[s]
is one of three unit vectors at
2