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Quadratic kernels and their ultraviolet limit · Part 4

A Wilson Yang–Mills Construction: A Natural-Language Mathematical Exposition

restores the finite-torus normalizations; and Section 5.20 gives reciprocal-shift and reflection compatibility. Together these prove the analytic predictor and its actual stationary response, including the harmonic fibre.

The regular dual predictor on two-forms

Continue the filled-potential-response notation. Let Hf(q) and Hc(p) be the fine and coarse pulse
metrics, d = d1(p) and δ = dL
1 (q0). The adjoint d∗on real momentum is continued analytically
using −p. Write Fr(q) = hingesr(q) for the patch multiplier on r-forms, and Vr(q) = fluxr(q) for
its transposed symbol at −q. Define
Source page 37.
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Continue the filled-potential-response notation. Let Hf(q) and Hc(p) be the fine and coarse pulse
metrics, d = d1(p) and δ = dL
1 (q0). The adjoint d∗on real momentum is continued analytically
using −p. Write Fr(q) = hingesr(q) for the patch multiplier on r-forms, and Vr(q) = fluxr(q) for
its transposed symbol at −q. Define
Λ = m(q0)−1 mask2
�RL(q0,a)−1,
y = |m(q0)|2hc/hf(q0),
xa = Ta/ga,
B = Hf(q0)
diagpairs(xa + xc) −S mask2(x)
,
M = diag(ga).
Source page 37.
Searchable transcription
Λ = m(q0)−1 mask2
RL(q0,a)−1,
y = |m(q0)|2hc/hf(q0),
xa = Ta/ga,
B = Hf(q0)
diagpairs(xa + xc) −S mask2(x)
,
M = diag(ga).

Here diagpairs sums the two coordinate entries in each two-form orientation. The principal wire is the regular expression

W0 = yV2(q0)
+
BΛdM −Hf(q0)Λd diag(Ta)
d∗.
Source page 37.
Searchable transcription
W0 = yV2(q0)
+
BΛdM −Hf(q0)Λd diag(Ta)
d∗.

For a vector x = (xa), let mask2(x) have diagonal entries xaxc at orientation {a, c}, and let diagpairs(xa + xc) have entries xa + xc. The entrywise identity

I −mask2(1 −Sx) = S
diagpairs(xa + xc) −S mask2(x)

Source page 37.
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I −mask2(1 −Sx) = S
diagpairs(xa + xc) −S mask2(x)

and covariance identity (3) prove
Source page 37.
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and covariance identity (3) prove
SB = Hf(q0) −yV2(q0)Hc(p)F2(q0),
Source page 37.
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SB = Hf(q0) −yV2(q0)Hc(p)F2(q0),
by substitution in each two-form diagonal entry. Together with F2(q0)Λ = I and F2(q0)δ =
dF1(q0), this identifies W0 with the original stationary dual expression for p ̸= 0. Every factor of
the displayed regular expression is uniformly analytic, so it extends the response through zero.
For l ̸= 0, set Rl = blow2
l hf(ql) and yl = |m(ql)|2hc/Rl, and put
Source page 37.
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by substitution in each two-form diagonal entry. Together with F2(q0)Λ = I and F2(q0)δ =
dF1(q0), this identifies W0 with the original stationary dual expression for p ̸= 0. Every factor of
the displayed regular expression is uniformly analytic, so it extends the response through zero.
For l ̸= 0, set Rl = blow2
l hf(ql) and yl = |m(ql)|2hc/Rl, and put
N = S2I −SHc(p)dMd∗.
Source page 37.
Searchable transcription
N = S2I −SHc(p)dMd∗.

The remaining wire branches are

Wl = Hf(ql)dL
1 (ql) diag(Dl,a)V1(ql)d∗
+ylV2(ql)N.
Source page 37.
Searchable transcription
Wl = Hf(ql)dL
1 (ql) diag(Dl,a)V1(ql)d∗
+ylV2(ql)N.

These are the nonprincipal dual branches, called stake in the source. The identities portD = scaleD, portR = scaleR and N = S2(I −cloud) on the regular set identify them with the original dual response. Their nonzero-alias divisor is separated, so no principal denominator is inverted. The lower bound gives R−1 l = O(grade(l)−4) and Dl = O(grade(l)−2) with the common analytic bounds. Signal and smoothing-flux factors then give C decayj(l), as for the bounded principal branch. Section 5.20 gives the reciprocal-shift and reflection identities needed for Fourier export. The algebra here identifies the regular symbols themselves.

Cumulative filters and propagation of the quadratic covariance

The cumulative-filter calculation closes the quadratic argument. Each one-step identity is composed along the same scale history, and the weighted alias sums remain absolutely convergent. The resulting covariance is therefore attached to the constructed history, rather than to an independently chosen continuum kernel. These identities are later used as the fixed linear comparison in the nonlinear predictor and in the free hierarchy.

A finite linear history begins at smoothing order j. It is either empty, or consists of a patch with odd block side L ≥3, new order J with j ≤J ≤j + 1, followed by a history beginning at J. Let Mv be the product of its block sides, with M∅= 1. For the centered one-dimensional box filter pL, write

3
Y
AL(p) =
ν=0
pL(pν).
Source page 38.
Searchable transcription
3
Y
AL(p) =
ν=0
pL(pν).

Its exact composition identity for odd sides is

ALM(p) = AL(Mp)AM(p).
Source page 38.
Searchable transcription
ALM(p) = AL(Mp)AM(p).
Define an extra filter recursively by E∅= 1 and
Source page 38.
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Define an extra filter recursively by E∅= 1 and
E(L,J;v)(p) = ALMv(p)J−jEv(p),
Sv(p) = AMv(p)jEv(p).
Source page 38.
Searchable transcription
E(L,J;v)(p) = ALMv(p)J−jEv(p),
Sv(p) = AMv(p)jEv(p).
The composition identity gives
Source page 38.
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The composition identity gives
S(L,J;v)(p) = AL(Mvp)JSv(p).
(QF1)
Source page 38.
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S(L,J;v)(p) = AL(Mvp)JSv(p).
(QF1)

The exponent J −j is zero or one. Thus extra smoothing factors enter at the successive cumulative lengths, while the principal filter has exactly the original exponent j.

The filters are entire, periodic under reciprocal integer translations, invariant under signed coordinate permutations, equal to one at zero, and satisfy Sv(p) = Sv(−p). These statements follow first for the finite box sums, then for AL, Ev, Sv by finite products and induction.

There is a bound independent of both the number of steps and the total dilation. On the strip | Im pν| ≤z/L0, a box filter satisfies

|AM(p)| ≤e4zM/L0.
Source page 38.
Searchable transcription
|AM(p)| ≤e4zM/L0.

When M ≤L0, at real principal momenta p/L0 in the fixed domain one also has

|AM(p/L0)| ≥e−4cboxM/L0.
Source page 38.
Searchable transcription
|AM(p/L0)| ≥e−4cboxM/L0.

For a history of total mass Mv ≤L0, induction using each block side at least three gives

|Ev(p)| ≤e8zMv/L0,
|Ev(p/L0)| ≥e−8cboxMv/L0.
(QF2)
Source page 38.
Searchable transcription
|Ev(p)| ≤e8zMv/L0,
|Ev(p/L0)| ≥e−8cboxMv/L0.
(QF2)

To check the induction, a new extra factor costs 4zMv/L0 in the upper exponent, and the preceding bound costs at most 8zMv/(3L0). Their sum is at most 8zMv/L0. If no extra factor occurs, monotonicity of the mass suffices. The lower bound has exactly the same calculation with negative exponents and cbox in place of z.

At an alias indexed by l, the principal box estimate is

|AM(aliasl(p))| ≤B4 mix(l)−1.
Source page 38.
Searchable transcription
|AM(aliasl(p))| ≤B4 mix(l)−1.

Combining this with (QF2), with L0 = Mv, proves

|Sv(aliasl(p))| ≤B4je8z mix(l)−j.
(QF3)
Source page 39.
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|Sv(aliasl(p))| ≤B4je8z mix(l)−j.
(QF3)

At the real principal alias the lower bound is

|Sv(p/Mv)| ≥e−4jcbox−8cbox > 0.
(QF4)
Source page 39.
Searchable transcription
|Sv(p/Mv)| ≥e−4jcbox−8cbox > 0.
(QF4)

These bounds are uniform over all finite histories, with constants depending on the initial order only. In particular all alias-filter functions have a common holomorphic neighborhood and the indicated uniform alias decay. Include now the longitudinal edge box filter rM(pa), and set

Dv,a(p) = Sv(p)rMv(pa),
PL,J,a(p) = AL(p)JrL(pa),
Y (f)(p) = f(p)f(−p).
Source page 39.
Searchable transcription
Dv,a(p) = Sv(p)rMv(pa),
PL,J,a(p) = AL(p)JrL(pa),
Y (f)(p) = f(p)f(−p).

The exact rail composition and (QF1) imply

D(L,J;v),a(p) = PL,J,a(Mvp)Dv,a(p).
(QF5)
Source page 39.
Searchable transcription
D(L,J;v),a(p) = PL,J,a(Mvp)Dv,a(p).
(QF5)

On real momenta Dv,a(−p) = Dv,a(p), so Y (Dv,a) = |Dv,a|2 ≥0. For any scalar symbol f, define its propagated alias sum by

Fv,af(p) = M−2
v
X
l∈(Z/MvZ)4
Y (Dv,a)(aliasl(p))f(aliasl(p)).
(QF6)
Source page 39.
Searchable transcription
Fv,af(p) = M−2
v
X
l∈(Z/MvZ)4
Y (Dv,a)(aliasl(p))f(aliasl(p)).
(QF6)
The normalization is M−2
v . Define LL,J,a by the same formula for one patch. The radix bijection
between aliases of LMv and pairs of aliases of L and Mv, together with (QF5), gives the exact
identity
F(L,J;v),af = LL,J,a(Fv,af).
(QF7)
Source page 39.
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The normalization is M−2
v . Define LL,J,a by the same formula for one patch. The radix bijection
between aliases of LMv and pairs of aliases of L and Mv, together with (QF5), gives the exact
identity
F(L,J;v),af = LL,J,a(Fv,af).
(QF7)
Indeed substitute the nested alias formula in the sum, factor out the outer Y (PL,J,a) by periodicity,
and use (LMv)−2 = L−2M−2
v . The empty history has F∅,af = f.
Every renormalization step adds an independent local covariance k−1. Let Nv be the sum of
the covariances of these noises propagated through their respective prefixes. More explicitly the
empty history has no prefixes; extending a history introduces the empty prefix and extends each
old prefix by the new patch. Thus
Source page 39.
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Indeed substitute the nested alias formula in the sum, factor out the outer Y (PL,J,a) by periodicity,
and use (LMv)−2 = L−2M−2
v . The empty history has F∅,af = f.
Every renormalization step adds an independent local covariance k−1. Let Nv be the sum of
the covariances of these noises propagated through their respective prefixes. More explicitly the
empty history has no prefixes; extending a history introduces the empty prefix and extends each
old prefix by the new patch. Thus
N∅= 0,
N(L,J;v),a = 1 + LL,J,aNv,a.
Source page 39.
Searchable transcription
N∅= 0,
N(L,J;v),a = 1 + LL,J,aNv,a.

If λ(p) is the initial Wilson quadratic divisor, the cumulative diagonal covariance is

Dv,a = Fv,a(λ−1) + k−1Nv,a.
Source page 39.
Searchable transcription
Dv,a = Fv,a(λ−1) + k−1Nv,a.

Linearity and (QF7) prove the feedback equation

D(L,J;v),a = LL,J,aDv,a + k−1.
(QF8)
Source page 39.
Searchable transcription
D(L,J;v),a = LL,J,aDv,a + k−1.
(QF8)

This formula accounts for every earlier noise; retaining only the final noise would give a different covariance. All sums are finite. Real nonnegativity follows term by term when k > 0, and reciprocal periodicity, evenness and covariance under signed coordinate permutations follow by the corresponding permutation of aliases.

Separating the principal alias in (QF6) yields the pole decomposition

Dv,a(p) = Y (Dv,a)(p/Mv)
λMv(p)
+ Hv,a(p) + k−1Nv,a(p),
(QF9)
Source page 40.
Searchable transcription
Dv,a(p) = Y (Dv,a)(p/Mv)
λMv(p)
+ Hv,a(p) + k−1Nv,a(p),
(QF9)
where λMv includes the M2
v scaling of the principal divisor and
Source page 40.
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where λMv includes the M2
v scaling of the principal divisor and
Hv,a(p) =
X
Y (Dv,a)(aliasl(p))
M2v λ(aliasl(p))
.
l̸=0
Source page 40.
Searchable transcription
Hv,a(p) =
X
Y (Dv,a)(aliasl(p))
M2v λ(aliasl(p))
.
l̸=0

This is an algebraic identity on the regular set of the denominators. The auxiliary divided symbols are not asserted to be continuous extensions at harmonic momenta. Their regular parts and their harmonic reconstruction are handled by the pole-removal construction already given above. Both H and the propagated noise are nonnegative on real regular momenta, and (QF4) supplies the uniform nonvanishing principal numerator required there.

The one-dimensional filters in this construction are literal normalized finite sums:

M−1
X
u=0
eiuz,
pM(z) = 1
M−1
X
rM(z) = 1
u=0
ei(u−⌊M/2⌋)z.
M
M
Source page 40.
Searchable transcription
M−1
X
u=0
eiuz,
pM(z) = 1
M−1
X
rM(z) = 1
u=0
ei(u−⌊M/2⌋)z.
M
M

Partitioning the indices 0, . . . , LM −1 as Mu + v proves rL(Mz)rM(z) = rLM(z). For odd sides the centers satisfy M⌊L/2⌋+ ⌊M/2⌋= ⌊LM/2⌋, proving the corresponding identity for p. The principal lower bound used in (QF2) has coefficient one in front of its exponential, which is essential for arbitrarily long histories. To derive it, choose a disk on which

c−|z| ≤|eiz −1| ≤c+|z|.
Source page 40.
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c−|z| ≤|eiz −1| ≤c+|z|.

Such positive constants exist because the ratio extends continuously with nonzero value at zero, and the disk excludes the other zeros. The geometric-sum identity

MrM(z)(eiz −1) = eiMz −1
Source page 40.
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MrM(z)(eiz −1) = eiMz −1

gives |pM(z)| = |rM(z)| ≥c0 for real z with M|z| in that disk, where c0 = min(1, c−/c+) > 0. If M ≤L0 and L0|z| ≤R0, the centered finite sum also gives

|pM(z) −1| ≤c+R0 M/L0.
Source page 40.
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|pM(z) −1| ≤c+R0 M/L0.

Put x = M/L0, k0 = c+R0, and u = |pM(z)|. Then u ≥c0 and u + k0x ≥1. Since ey ≥1 + y,

uek0x/c0 ≥u + uk0x/c0 ≥u + k0x ≥1.
Source page 40.
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uek0x/c0 ≥u + uk0x/c0 ≥u + k0x ≥1.

Thus u ≥e−(k0/c0)x. This proves the stated principal estimate with cbox = k0/c0, without multiplying a fixed prefactor less than one at every step. The complex-strip upper bound follows simply by bounding every exponential in the centered average by eM| Im z|.

Source: A Wilson Yang–Mills Construction: A Natural-Language Mathematical Exposition. Both papers belong to one Zenodo record. No external funding.