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Shadow Theory

Section 6 9 October 2026

A smooth scalar gate which copies the entry sign

Reading position 7 of 16

6 A smooth scalar gate which copies the entry sign

Let q=(x,z)q=(x,z) and fix A≥20A\geq20, 0<ε≤10−30<\varepsilon\leq10^{-3}. Use a smooth monotone step with all endpoint derivatives zero. On the first interval [0,ε][0,\varepsilon] interpolate from

Hb=HA(x)+Ho(z) H_b=H_A(x)+H_{\rm o}(z)

to

Hq=−Δq+14qTKqq,Kq=(13/8−5/8−5/813/8). H_q=-\Delta_q+\tfrac14q^\mathsf TK_q q,\qquad K_q=\begin{pmatrix}13/8&-5/8\\-5/8&13/8\end{pmatrix}.

Keep HqH_q until 2π−ε2\pi-\varepsilon, then interpolate to Ha=Ho(x)+HA(z)H_a=H_{\rm o}(x)+H_A(z) on the final interval. The ramp intervals are contained in the duration 2π2\pi. They are not appended to the commensurate time.

The two normal frequencies of HqH_q are 11 and 3/23/2. Consequently its unmodified duration-2π2\pi wave operator is −i SWAPxz-i\,\mathrm{SWAP}_{xz}. The smooth gate just defined is a different propagator; no exact factor scratch reset will be inferred from that observation. Its true entrance is RA(x)φ(z)R_A(x)\varphi(z) and its record must match the actual entry sign of xx. This is a path statement requiring a complete-current estimate.

6.1 The coherent Gaussian comparison

For s=±1s=\pm1, replace the initial and final nonlinear holding wells by

Hb,s=−Δ+{(x−sA)2+z2}/4−1/2,Ha,s=−Δ+{x2+(z−sA)2}/4−1/2, H_{b,s}=-\Delta+\{(x-sA)^2+z^2\}/4-1/2,\qquad H_{a,s}=-\Delta+\{x^2+(z-sA)^2\}/4-1/2,

using the same ramps and middle HqH_q. Let ψs\psi_s be the exact Gaussian evolution of φ(x−sA)φ(z)\varphi(x-sA)\varphi(z), and set

χ=ψ++ψ−2(1+e−A2/2). \chi=\frac{\psi_++\psi_-}{\sqrt{2(1+e^{-A^2/2})}} . (6.1)

Both common and relative phases are retained in these exact quadratic evolutions. The comparison is not a population mixture. It need not stay normalized, but ∥χ∥≤2\|\chi\|\leq\sqrt2.

Lemma 6.1 (Finite-ramp Gaussian tube)

The position centers are ±M(τ)\pm M(\tau) and the common position covariance and centered velocity matrix are Σ,B\Sigma,B. On the gate,

∣M∣>.29A,∣M′∣<1.35A,∣(M/∣M∣)′∣<5,.4I≤Σ≤1.1I,∥B∥<1. |M|>.29A,\quad |M'|<1.35A,\quad |(M/|M|)'|<5,\quad .4I\leq\Sigma\leq1.1I,\quad \|B\|<1. (6.2)

On each ramp in its corresponding well coordinate, at the final endpoint, and under the subsequent matched harmonic comparison hold,

.9I≤Σ≤1.1I,∥B∥≤.2,∣mx∣≤A/20,∣mz−sA∣≤A/20,∣p∣≤A/20, .9I\leq\Sigma\leq1.1I,\quad\|B\|\leq.2,\quad |m_x|\leq A/20,\quad |m_z-sA|\leq A/20,\quad |p|\leq A/20, (6.3)

with x,zx,z exchanged at the entrance. Every ordered word of degree at most two in x,z,Px,Pzx,z,P_x,P_z, applied to χ\chi, has norm at most G=100(A+2)2G=100(A+2)^2.

Proof

For the unswitched sensor the center is

Mq=A2(cos⁡τ+cos⁡(3τ/2), cos⁡τ−cos⁡(3τ/2)). M_q=\frac A2 \big(\cos\tau+\cos(3\tau/2),\, \cos\tau-\cos(3\tau/2)\big).

Writing v=cos⁡2(τ/2)v=\cos^2(\tau/2) gives 2∣Mq/A∣2=16v3−20v2+5v+12|M_q/A|^2=16v^3-20v^2+5v+1. Its minimum is 83/108−510/27>9/5083/108-5\sqrt{10}/27>9/50, so ∣Mq∣>.3A|M_q|>.3A and ∣Mq′∣≤13/8A<4A/3|M_q'|\leq\sqrt{13/8}A<4A/3. The sensor fundamental matrix in (q,P)(q,P) has norm at most 3/23/2. The difference generator is at most 5/45/4 and is supported for total length 2ε2\varepsilon. Volterra's equation therefore gives

∥F−Fq∥≤32(e15ε/4−1),∥F∥≤32e15ε/4. \|F-F_q\|\leq\tfrac32(e^{15\varepsilon/4}-1),\qquad \|F\|\leq\tfrac32e^{15\varepsilon/4}.

The opposite affine forces contribute at most 3εe15ε/4A3\varepsilon e^{15\varepsilon/4}A to the phase-space center difference. Their sum with the preceding homogeneous error is less than .009A.009A, by ea≤(1−a)−1e^a\leq(1-a)^{-1}. This proves the center bounds and 1.35/.29<51.35/.29<5 proves the normal bound.

The exact sensor position covariance has eigenvalues 11 and cos⁡2(3τ/2)+(4/9)sin⁡2(3τ/2)\cos^2(3\tau/2)+(4/9)\sin^2(3\tau/2). Its centered velocity norm is at most 5/85/8. The fundamental-matrix bounds imply ∥FFT−FqFqT∥<.02\|FF^\mathsf T-F_qF_q^\mathsf T\|<.02. Block inversion in B=ΓPqΣ−1B=\Gamma_{Pq}\Sigma^{-1} gives

∥B∥<58+150(52+589452)<1. \|B\|< \tfrac58+\tfrac1{50} \left(\tfrac52+\tfrac58\tfrac94\tfrac52\right)<1.

On the ramps FqF_q is within (27/8)ε(27/8)\varepsilon of the identity or endpoint swap, whence ∥F−Iendpoint∥<.01\|F-I_{\rm endpoint}\|<.01 and the Wigner covariance error is less than .021.021. Together with the center error these imply (6.3); orthogonal harmonic phase-space evolution preserves these bounds during the matched hold. Lastly the means are bounded by 1.6A1.6A and phase-space variances by 33. Gaussian fourth moments, plus the commutator correction [qi,Pj]=2iδij[q_i,P_j]=2i\delta_{ij}, bound degree-two ordered words; coherent summation costs at most 2\sqrt2. The stated 100(A+2)2100(A+2)^2 bounds each of these terms.

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6.2 Localized forcing and the shifted energy graph

Put c=4A2+4c=4A^2+4, K(τ)=H(τ)+cK(\tau)=H(\tau)+c, and

λ=154A2+72,BA=2⋅106(A+1)10e−A2/10,h0=105(A+2)6e−A2/4. \lambda=\tfrac{15}4A^2+\tfrac72,\qquad B_A=2\cdot10^6(A+1)^{10}e^{-A^2/10},\qquad h_0=10^5(A+2)^6e^{-A^2/4}. (6.4)

Here λ\lambda is a lower bound on the positive shifted potential, not a spectral cutoff.

Lemma 6.2 (Localized graph error)

For the true wave ψ\psi and comparison (6.1), E=ψ−χE=\psi-\chi obeys

sup⁡gate∥K(τ)E(τ)∥≤hg:=e8(h0+2εBA),∥KholdE(t)∥≤hg+tBA.\begin{align}\sup_{\rm gate}\|K(\tau)E(\tau)\| &\leq h_g:=e^8(h_0+2\varepsilon B_A),\tag{6.5}\\ \|K_{\rm hold}E(t)\|&\leq h_g+tB_A . \tag{6.6}\end{align}

Every ordered position/momentum word of degree at most two on these errors is bounded by 15hg15h_g on the gate and 15(hg+tBA)15(h_g+tB_A) on the two-coordinate hold.

Proof

The nonlinear well differs from its ss-centered harmonic comparison by

Ds(r)=A24sech⁡2(Ar)+Ar2(s−tanh⁡Ar),Ds′=−A32ST+A2(s−T)−A2r2S,Ds′′=A4ST2−A42S2−A2S+A3rST,S=sech⁡2(Ar),T=tanh⁡(Ar).\begin{aligned}D_s(r)&=\tfrac{A^2}4\operatorname{sech}^2(Ar) +\tfrac{Ar}2(s-\tanh Ar),\\ D_s'&=-\tfrac{A^3}2ST+\tfrac A2(s-T)-\tfrac{A^2r}2S,\\ D_s''&=A^4ST^2-\tfrac{A^4}2S^2-A^2S+A^3rST, \qquad S=\operatorname{sech}^2(Ar),\quad T=\tanh(Ar). \end{aligned}

Each absolute value is bounded globally by 100(A+1)4(1+∣r∣)100(A+1)^4(1+|r|). On the own collar sr≥A/4sr\geq A/4 the same bound gains e−A2/2e^{-A^2/2}, using S≤4e−2A∣r∣S\leq4e^{-2A|r|} and 1−sT≤2e−2A∣r∣1-sT\leq2e^{-2A|r|}.

For a ramp or hold branch write ξ=q−m\xi=q-m. The strict tube gives

∣∂iψs∣≤(∣ξ∣+A/10)∣ψs∣,∣∂i∂jψs∣≤{(∣ξ∣+A/10)2+1}∣ψs∣, |\partial_i\psi_s|\leq(|\xi|+A/10)|\psi_s|,\qquad |\partial_i\partial_j\psi_s| \leq\{(|\xi|+A/10)^2+1\}|\psi_s|,

and the shifted potential is at most 20(A+1)2(1+∣ξ∣)220(A+1)^2(1+|\xi|)^2. Since 1+∣r∣≤2(A+1)(1+∣ξ∣)1+|r|\leq2(A+1)(1+|\xi|), the identity K(Dsψs)=DsKψs−2Ds′∂rψs−Ds′′ψsK(D_s\psi_s)=D_sK\psi_s-2D_s'\partial_r\psi_s-D_s''\psi_s gives the explicit envelope

∣K(Dsψs)∣≤5400(A+1)7(1+∣ξ∣)3w(r)∣ψs∣. |K(D_s\psi_s)| \leq5400(A+1)^7(1+|\xi|)^3 w(r)|\psi_s|. (6.7)

Indeed the three terms have coefficients at most 4800,400,2004800,400,200, respectively. Here w=e−A2/2w=e^{-A^2/2} on the own collar and 11 outside.

We include the Gaussian integration which supplies the exponential in (6.4). The density is dominated by 11/911/9 times the isotropic two-dimensional normal density of variance 11/1011/10. Outside the collar, the normal centered coordinate is below −.7A-.7A. Set a=.7A/11/10>1a=.7A/\sqrt{11/10}>1. Repeated integration by parts gives

∫a∞u6γ(u) du=(a5+5a3+15a)γ(a)+15Φ(−a). \int_a^\infty u^6\gamma(u)\,du =(a^5+5a^3+15a)\gamma(a)+15\Phi(-a).

Using Φ(−a)≤γ(a)/a\Phi(-a)\leq\gamma(a)/a and (1+∣ξ∣)6≤35(1+∣ξ1∣6+∣ξ2∣6)(1+|\xi|)^6\leq3^5(1+|\xi_1|^6+|\xi_2|^6), its outside weighted square-root moment is at most

92(A+1)3e−A2/10. 92(A+1)^3e^{-A^2/10}.

For explicit constants, the squared polynomial prefactor is bounded by (11/9) 243 70 (2/5)<8400<922(11/9)\,243\,70\,(2/5)<8400<92^2, while a2/4=49A2/440>A2/10a^2/4=49A^2/440>A^2/10. On the whole Gaussian, E(1+∣ξ∣)6≤32[1+48(11/10)3]<2100<462\mathbb E(1+|\xi|)^6\leq32[1+48(11/10)^3]<2100<46^2. The inside contribution is therefore at most 46e−A2/246e^{-A^2/2}. Since 5400(46+92)<1065400(46+92)<10^6, (6.7) gives ∥K(Dsψs)∥≤106(A+1)10e−A2/10\|K(D_s\psi_s)\|\leq10^6(A+1)^{10}e^{-A^2/10}. Coherent summation yields BAB_A. This forcing is present only on the two ramps during the gate, and throughout the nonlinear hold.

Next write W=V+cW=V+c. Direct use of the expression for UAU_A gives

W≥∣q∣2/8+λ,∥ΔW∥∞≤M:=A4+32A2+2. W\geq |q|^2/8+\lambda,\qquad \|\Delta W\|_\infty\leq M:=A^4+\tfrac32A^2+2.

For compact smooth vectors,

∥Kf∥2=∥Δf∥2+∥Wf∥2+2∫W∣∇f∣2−∫ΔW ∣f∣2. \|Kf\|^2=\|\Delta f\|^2+\|Wf\|^2+ 2\int W|\nabla f|^2-\int\Delta W\,|f|^2. (6.8)

Positivity gives ∥f∥≤∥Kf∥/λ\|f\|\leq\|Kf\|/\lambda, and hence ∥Wf∥,∥Δf∥≤1+M/λ2∥Kf∥\|Wf\|,\|\Delta f\|\leq\sqrt{1+M/\lambda^2}\|Kf\|. For A≥20A\geq20, M/λ≤2/7\sqrt M/\lambda\leq2/7. The switching multiplier satisfies

∣Dsw∣≤3∣q∣2/8+7A2/4+1/2≤3W, |D_{\rm sw}|\leq3|q|^2/8+7A^2/4+1/2\leq3W,

so ∥Dswf∥≤4∥Kf∥\|D_{\rm sw}f\|\leq4\|Kf\|. The equation for KEKE consequently costs at most 4∣η′∣∥KE∥+∥KR∥4|\eta'|\|KE\|+\|K\mathcal R\|, where η\eta is the ramp weight and R\mathcal R is the complete coherent forcing. The total variation of the two ramps is 22. Gronwall gives (6.5); the static hold has no time-graph cost and gives (6.6).

For completeness, the entrance graph bound is a wave estimate. On r≥0r\geq0, put a=φ(r−A)a=\varphi(r-A), b=φ(r+A)b=\varphi(r+A), t=b/a=e−Art=b/a=e^{-Ar} and h(t)=1+t−1+t2h(t)=1+t-\sqrt{1+t^2}. Then 0≤h≤t0\leq h\leq t, ∣h′∣,∣h′′∣≤1|h'|,|h''|\leq1. The differences between (a+b)/2(a+b)/\sqrt2 and RAR_A and their first two derivatives are bounded respectively by b/2b/\sqrt2 times

1,r/2+3A/2,r2/4+3Ar/2+13A2/4+1/2. 1,\qquad r/2+3A/2,\qquad r^2/4+3Ar/2+13A^2/4+1/2 .

Reflect on the negative half-line. For k≥0k\geq0,

∫∣r∣kmin⁡{γ(r−A),γ(r+A)} dr≤k!e−A2/2, \int |r|^k\min\{\gamma(r-A),\gamma(r+A)\}\,dr \leq k!e^{-A^2/2},

because e−Ar≤e−re^{-Ar}\leq e^{-r} for A≥1A\geq1 and 2/2π<12/\sqrt{2\pi}<1. The normalization correction is bounded by 1−(1+e−A2/2)−1/2≤e−A2/2/21-(1+e^{-A^2/2})^{-1/2}\leq e^{-A^2/2}/2. Gaussian moments and reordering Pr=rP−2iP r=rP-2i now bound every degree-two entrance error word by 400(A+1)2e−A2/4400(A+1)^2e^{-A^2/4}. The elementary quadratic bound on UAU_A and the shift cc then give the larger, convenient ∥K(0)E(0)∥≤h0\|K(0)E(0)\|\leq h_0.

Finally (6.8) bounds each degree-two word: position squares use ∥∣q∣2f∥≤8∥Wf∥\||q|^2f\|\leq8\|Wf\|; momentum products use Fourier ∥∂i∂jf∥≤∥Δf∥\|\partial_i\partial_jf\|\leq\|\Delta f\|; mixed words use its positive weighted-gradient term. Reordering adds at most 2∥f∥2\|f\|, and lower words follow by interpolation. All are below 15∥Kf∥15\|Kf\| with the displayed M/λ2M/\lambda^2 bound. These are derivative and moment estimates, not consequences of wave norm alone.

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6.3 From the complete current to the receiver's own record

Set Kg=15hgK_g=15h_g and define

Fcg=256(A+1)e−A2/27,Feg=1000(KgG+Kg2),Bend=2A(e−2A2/25+e−2A2/5),Eend=3hgλ+(hg/λ)2,Fcopy=Fcg+Feg+Bend+Eend.\begin{align}F_{\rm cg}&=256(A+1)e^{-A^2/27},& F_{\rm eg}&=1000(K_gG+K_g^2),\tag{6.9}\\ B_{\rm end}&=\frac2A \big(e^{-2A^2/25}+e^{-2A^2/5}\big),& E_{\rm end}&=\frac{3h_g}{\lambda} +(h_g/\lambda)^2,\tag{6.10}\\ F_{\rm copy}&=F_{\rm cg}+F_{\rm eg}+B_{\rm end}+E_{\rm end}. \tag{6.11}\end{align}
Proposition 6.3 (A different receiver records the entry sign)

Under the gate above, the actual probability that zz fails to finish in the region assigned to the entry sign of xx is at most CFcopyC F_{\rm copy}. The two regions are z≤−A/2z\leq-A/2 and z≥A/2z\geq A/2. The statement holds for arbitrary correlations in the original actual law subject to (5.2).

Proof

Use the plane n(τ)⋅q=0n(\tau)\cdot q=0, where n=M/∣M∣n=M/|M|. It starts at x=0x=0. A path changing its side must cross that spacetime surface. The relative current is j⋅n+ρ n′⋅qj\cdot n+\rho\,n'\cdot q on the plane. Expand the current of the full coherent sum before taking its absolute value. The diagonal branch terms are bounded by ∣ψs∣2(3A+6∣q∣)|\psi_s|^2(3A+6|q|); the two interference terms and moving-plane cross-density term together are bounded by ∣ψ+ψ−∣(12A+18∣q∣)|\psi_+\psi_-|(12A+18|q|). These follow from the Gaussian amplitude gradients −Σ−1(q−sM)/2-\Sigma^{-1}(q-sM)/2, phase velocities sM′+B(q−sM)sM'+B(q-sM), and (6.2).

Each branch's plane density is at most (2/3)e−A2/27(2/3)e^{-A^2/27}, since .292/(2⋅1.1)>1/27.29^2/(2\cdot1.1)>1/27 and (2π⋅.4)−1/2<2/3(2\pi\cdot.4)^{-1/2}<2/3. The conditional tangential mean has magnitude below AA and variance at most 1.11.1, so its conditional E∣q∣\mathbb E|q| is at most A+2A+2. Use ∣ψ+ψ−∣≤(∣ψ+∣2+∣ψ−∣2)/2|\psi_+\psi_-|\leq(|\psi_+|^2+|\psi_-|^2)/2 and the denominator in (6.1). The full plane flux is at most 30(A+1)e−A2/2730(A+1)e^{-A^2/27} per unit time. Integration over 2π<72\pi<7 is bounded by FcgF_{\rm cg}. No Gaussian branch has been sampled as the actual state.

The trace inequality for Hilbert-valued functions,

∥f∣n⋅q=0∥2≤2∥f∥ ∥∂nf∥, \|f|_{n\cdot q=0}\|^2 \leq2\|f\|\,\|\partial_nf\|,

applied also to ∂nf\partial_nf and the tangential position times ff, gives trace bounds 2Kg,3Kg,3Kg2K_g,3K_g,3K_g for the error and 2G,3G,3G2G,3G,3G for the comparison. Expanding the current difference gives at most 24KgG+12Kg224K_gG+12K_g^2 per unit time. Expanding the moving-surface density difference gives at most 60KgG+30Kg260K_gG+30K_g^2, since ∣n′∣<5|n'|<5. Integrating both over 2π<72\pi<7 gives FegF_{\rm eg}. These bounds explicitly retain the cross terms and the quadratic error current.

At the endpoint the plane need not be exactly z=0z=0. The strict tube gives ∣mx/mz∣≤1/19|m_x/m_z|\leq1/19. On ∣z∣≥A/2|z|\geq A/2, ∣x∣≤A|x|\leq A, the signs of n⋅qn\cdot q and zz agree. The complement under the coherent comparison is bounded by BendB_{\rm end}. Indeed the receiver mean is at least .45A.45A from its nearer middle boundary and the scratch mean at least .95A.95A from its outer boundary. The variance is at most 1.11.1; one-dimensional Mills bounds and ∣χ∣2≤∣ψ+∣2+∣ψ−∣2|\chi|^2\leq|\psi_+|^2+|\psi_-|^2 give the two displayed 2/A2/A terms with exponents 2A2/252A^2/25 and 2A2/52A^2/5. The true density adds at most 2∥χ∥∥E∥+∥E∥2≤Eend2\|\chi\|\|E\|+\|E\|^2\leq E_{\rm end}.

For the reference flow, spacetime coarea bounds the expected crossing count by the integrated absolute relative current. The prescribed scalar potentials are smooth in position, have at most quadratic growth, and have polynomially bounded spatial derivatives. Common oscillator domains and weighted differentiation propagate every finite Schwartz order of this entrance over the finite schedule. In the full configuration, normalization and Cauchy–Schwarz give

∥∂τρ∥1≤2∥∂τΨ∥2,∫∣j∣≤2∥∇Ψ∥2,∫∣j∣ ∣∇ρ∣ρ≤4∥∇Ψ∥22. \|\partial_\tau\rho\|_1\leq2\|\partial_\tau\Psi\|_2,\qquad \int|j|\leq2\|\nabla\Psi\|_2,\qquad \int\frac{|j|\,|\nabla\rho|}{\rho} \leq4\|\nabla\Psi\|_2^2 .

For a baker stage with complete bounded drift VV, the last two bounds acquire respectively ∥V∥∞\|V\|_\infty and 2∥V∥∞∥∇Ψ∥22\|V\|_\infty\|\nabla\Psi\|_2; its action also stays finite. The value on nodes is defined by the zero-current convention. Finite weighted graph propagation makes these quantities integrable on the finite schedule. The complete spacetime current (ρ,j)(\rho,j) is C1C^1, is conserved, and has unit mass at every time. In particular

∫0Tf ⁣∫ρ>0∣∂τρ+jρ⋅∇ρ∣ dq dτ<∞,∫0Tf ⁣∫∣j∣ dq dτ<∞. \int_0^{T_f}\!\int_{\rho>0} \left|\partial_\tau\rho+\frac{j}{\rho}\cdot\nabla\rho\right| \,dq\,d\tau<\infty, \qquad \int_0^{T_f}\!\int|j|\,dq\,d\tau<\infty.

The first follows by summing the displayed time-density and logarithmic current bounds; the second controls escape to infinity. There is no physical boundary or singular excluded set in this effective configuration space. These are the hypotheses of the general current criterion in [6, Theorem 1], which supplies almost-everywhere global flow and equivariance on the finite schedule. Thus coarea applies, including possible nodes through their reference-null path exclusion. The original cap (5.2) transfers the union of the crossing and endpoint events to the actual law, with the single factor CC. Selecting a sign and then reapplying a conditional cap is unnecessary.

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