
(Proposition 2); signed, it is the photon’s electric field. Neither carries the coupling, and the second
fails for a reason that applies to any low-level link variable (Proposition 3).
Proposition 2. Let
E
link
=
P
4
s
e
over the four served bonds, unsigned,
s
e
=
±
1
2
. The divergence
of
E
at a node is twice the signed sum of the twelve bonds incident on it, and at a void twice the
signed sum of the twelve bonds of the octahedron. The zero-divergence condition is “six up, six down”
on the twelve bonds of every check, and the code’s Z
2
checks are its parity.
Each incident bond uses two links at the node, one per path. The rest is bookkeeping, verified on
the lattice. The proposition says that the code’s checks are the mod-2 reduction of a
U
(1) constraint
the same bonds can carry. It does not say that this constraint is the photon’s Gauss law, and it is
not. In the dual description of Section 4, the photon’s Gauss law is the signed divergence at each
tetrahedral void, six bonds each, and its electric field on a
⟨
100
⟩
link is the signed circulation of the
bond field around the dual plaquette that link pierces, the four served bonds with orientation signs.
The unsigned cube-edge constraint of the proposition, lifted to
U
(1), is a different theory on the
same bonds (Appendix E): it has planar subsystem conservation laws and an anisotropic dispersion
(
ω
2
/k
2
= 2 along [100] with one flat polarization, 0
.
5 and 1
.
5 along [110]), not Maxwell’s. The
signed tetrahedral-divergence lift reproduces
ω
2
/k
2
= 1 for both polarizations in every direction to
five figures. So the code and the photon share the bonds but not the constraint: the code’s checks
are the parity of a U(1) structure that is not the photon.
Proposition 3. Low-level quantum-link variables cannot carry the observed coupling; substantially
more than three flux levels are required, and the link variable must be effectively rotor-like. Projector
Monte Carlo on the photon’s Gauss-law sector gives, for three electric-flux levels per
⟨
100
⟩
link,
α
−1
= 14 at
L
= 6 and 20
±
6 at
L
= 8, consistent with exact diagonalization at
L
= 2 (12
.
5); two
levels (
E
=
±
1
2
) give 7 at
L
= 6 (5
.
1 at
L
= 2). The infinite-volume value is of order 20–30. The
observed value at the confinement scale is 135.5.
The ring-exchange model of Appendix B with the electric flux on each
⟨
100
⟩
link restricted to
{−
1
,
0
,
1
}
is a spin-1 quantum link model on the node–void lattice; the five-level served-qubit sum
is bounded by the two- and three-level cases and the spin-2 case. Its ground state is positive in the
flux basis, so a projector Monte Carlo has no sign problem, and the transverse electric structure
factor at the smallest wavevector gives
p
J/U
=
S
T
/λ
k
directly, with no estimate and no calibration.
Exact diagonalization at
L
= 2, with
U
from the winding sector and
J
from a magnetic twist, gives
p
J/U
= 0
.
41 (spin-
1
2
) and 0
.
99 (spin-1); the Monte Carlo at
L
= 6 and 8 gives the values in the
proposition, with the
L
= 8 uncertainty set by the spread of the three lattice axes rather than the
nominal error. The two methods agree with each other and disagree by a factor of four with the
Gaussian sum-rule estimate of Appendix C, which is therefore retained only as a bound on level
counts. Methods, axis values and the k
2
extrapolation are in Appendix E.
The conclusion is the one emergent-gauge-theory studies reach for spin models generally [
23
,
10
]:
a
U
(1) built from low-level link variables is strongly coupled,
α ∼
0
.
1. Reaching 1
/
135 would need
p
J/U ≃
11 against the 1–2 found at two and three levels. How many levels that corresponds to is
not sharply determined here: the fluctuation bound of Appendix C gives at least seven, and that
bound is unreliable as an estimate, so we state only that the requirement is far above three and
the regime an effectively continuous rotor. So the link variable of the photon sector is a rotor, as
Definition 1 states, and its weak coupling is not a property of its state space but of its energy scales:
an explicit charging energy small against the plaquette stiffness,
U/J ≃
0
.
009. That is what (I1)–(I2)
of Section 8.1 assert and what (P2) and (P3) are shown to supply in Section 8.8, and it gives the
coupling a physical reading within the model: light couples weakly because the standing-information
8