
crete spacetime symmetries, and where it stops short of the physical electromagnetic charge. This
paper fills that gap at the level of root-system structure, and is careful to claim nothing beyond it.
Scope: structure, not dynamics. Every result below is a statement about the D
4
and F
4
root
systems, their automorphisms, and their representations. No action, Hilbert space, quantization,
gauge field, or S-matrix is constructed; no dynamics is proposed; and the recovery of continuum 4D
Lorentz invariance from the discrete lattice — a prerequisite for any “lattice = vacuum” program
— is a recognized open problem that this paper does not solve; Section 11 establishes only the
rotational part, that anisotropy is forbidden below sixth order. The grading label studied here is
therefore a discrete label with a physical motivation, not the electromagnetic charge of a constructed
U(1); the distinction is maintained throughout, and the identification of the two is listed among
the open problems. Because the label is Z
3
-valued, it can fix charge only modulo one; the integer
part, which separates +2/3 from −1/3, must come from elsewhere. The companion paper obtains
+2/3 by a translation-winding argument that lies outside the grading [2]; whether the two routes
describe the same charge is left open.
No charge commuting with the twisted su(3) can live in the bond algebra: Theorem 1 below
shows that its commutant in so(8) is trivial. The candidate examined instead is structural: the
grading label lives in the diamond-type extension of the lattice — the glue classes of D
∗
4
/D
4
, where
the matter representations and the trapped-node defects of Section 1.1 both sit. The results below
are what that proposal derives, computed blind: the structure was worked out first, and com-
parison with Standard Model assignments was made only afterward and is labeled as comparison
throughout.
Sections 2–5 work inside the bond algebra so(8): they rebuild the twist, show that it leaves no
room for a charge commuting with the twisted su(3), derive the grading label and its conjugation
rule, and end at a fence — within so(8), color-triplet matter is incompatible with the grading.
Sections 6–8 add matter to the algebra. Bonds and matter close into f
4
, the label becomes, up to
conjugation, a coweight, and the enlarged fixed subalgebra contains exactly one color under which
the charged matter is a triplet. Sections 9–12 state the coupling fence, the falsifiers, the isotropy of
the lattice, and what is and is not derived.
2 Setup
The D
4
root system is the set of 24 vectors ±e
i
± e
j
, 1 ≤ i < j ≤ 4, each of squared length 2.
Its twelve spatial roots ±e
i
± e
j
with i, j ≤ 3 are the twelve FCC nearest-neighbor bond directions
of a constant-time slice. The automorphism group of the root system, generated by reflections in
the 24 roots together with reflections in the 24 short vectors ±e
i
and (±1, ±1, ±1, ±1)/2, has order
1152, the Weyl group of F
4
; we verified this by explicit closure. It contains 80 elements of order 3.
Standard background on D
4
, its glue, and triality is in Refs. [4, 6].
Fix the stacking axis (1, 1, 1). The six spatial roots orthogonal to it span what we call the
geometric A
2
, the regular A
2
subalgebra of these bond roots, and the plane they span is the color
plane. Exactly two order-3 automorphisms of the root system fix these six roots pointwise (one pair
per stacking axis; eight in all across the four axes); call one of them τ . It acts as the identity on the
color plane and as a rotation by 2π/3 on the orthogonal plane spanned by u = (1, 1, 1, 0)/
√
3 and
e
4
. The Weyl group of D
4
has order 192, so the quotient Aut(D
4
)/W (D
4
) has order 6; τ lies outside
W (D
4
) and induces an outer automorphism of so(8), which is triality. The 18 remaining roots fall
into six τ -orbits of three, each orbit containing one spatial and two temporal roots. The twist is
σ = Ad
e
2πi ρ·H/3
◦ τ with ρ = e
1
− e
3
the Weyl vector of the geometric A
2
(simple roots e
1
− e
2
3