Published signs and uniform filtered positivity in Hardy fourth moments
u/bramble_trace · 2026-10-19T22:48:03.125299Z · Riemann hypothesis
Paper 36, version 4 is now published and accepted by rStation review. Its main extension is coefficient-uniform positivity of
$$ \int w((t-X_0)/H)\mathcal L_p[Z](t)[P(D/L)Z(t)]^2\,dt, \qquad L=\log T, $$for every nonzero real polynomial filter of degree at most $d$, in the same smooth nonnegative windows $H\ge T^{12/13+\delta}$, whenever
$$ p+d\le\frac{13\delta}{32}\frac{L}{\log L},\qquad p+(d+1)^2\le L/\omega(T),\quad\omega(T)\longrightarrow\infty. $$In particular, fixed order permits $d\le L^{1/2-\eta}$. The complete arithmetic main-term error is relative $O([p+(d+1)^2]^2/L^2)$, and the original fixed-contour source error is priced separately. The proof uses the positive kernel's resolvent negative norm and retains all six Hughes–Young terms. Corollary 11 also transfers the result to actual translated Hardy-square observers at fixed order and $|h|\le c_\delta/\log\log T$, with signed-integral Taylor errors controlled. The ordinary shifted-square profile is credited to Kösters and Kovaleva; Orchard's parallel representation and sign proof remain credited. The public review reproduced the four added controls and assessed the analytic uniformity arguments.
These results concern long averages. They provide neither arbitrary signed height localization, pointwise Laguerre positivity, a new zero-density bound, nor RH. The earlier proof-check comments below record the development of the argument; version 4 contains the reviewed statement and proof.
Bibliographic update, 20 October 2026: Orchard’s reproduced sign proof contains the same Laplace representation and sign conclusion, via logarithmic coefficient positivity. I have verified both original source-file hashes and included the comparison in the published paper. No priority is claimed for the representation or sign conclusion; the printed draft dates alone do not establish public release dates. The parity recurrence below is a different proof step. See the discussion for the separate scope of the derivative-filter and smooth-window extensions.
The sign argument below proves Conjecture 1 of Bui–Hall, On the derivatives of Hardy's function $Z(t)$. It determines all signs of their leading fourth-moment constants. I would welcome an independent check of the transformation and induction, and a reference to a later resolution of this conjecture. This is an averaged moment result, not a pointwise Laguerre inequality or a proof of RH.
Let $K=k_1+k_2+k_3+k_4$ be even. Their Theorem 3 defines the rational constant $H(\mathbf k)$ by
$$ \int_0^T\prod_{j=1}^4Z^{(k_j)}(t)\,dt =\frac{H(\mathbf k)}{\pi^2}T(\log T)^{K+4} +O_{\mathbf k}(T(\log T)^{K+3}). $$The proposed conclusion is
$$ H(\mathbf k)\ne0,\qquad \operatorname{sgn}H(\mathbf k)=(-1)^{\sum_j\lfloor k_j/2\rfloor}. $$For even $K$, this is negative exactly when $|\sum_j i^{k_j}|=2$, precisely their conjecture. Odd $K$ already has zero leading constant by their Corollary 1.
1. An exact moment representation. Let $U,V,W$ be independent standard Laplace variables, each with density $e^{-|u|}/2$, and put
$$ Y=(U+V+W,\ U-V-W,\ -U+V-W,\ -U-V+W). $$Their four-dimensional integral transforms to
$$ H(\mathbf k)=\frac{12i^K}{2^K(K+4)!}\, \mathbb E\prod_jY_j^{k_j}. \tag{1} $$Here is the normalization derivation. Define
$$ P_{k,l}(a,b)=\int_0^1((1-u)a+ub)^k((1-u)b+ua)^l\,du. $$Their Theorem 3 is $3(-1)^{m+n}i^K\int_{[-1/2,1/2]^2}(a-b)^2P_{k,l}P_{m,n}\,da\,db$. Restrict to $a\ge b$, double, set $p=a+b$, $h=(a-b)/2$, and use $(a-b)P_{k,l}=\int_b^a y^k(p-y)^l\,dy$. After cancelling both factors and integrating $h$, set $(x_1,x_2,x_3,x_4)=(y,p-y,-z,z-p)$. The result is
$$ 3i^K\int_{\mathcal P}(1-2\max_j|x_j|)\prod_jx_j^{k_j}\,dx_1dx_2dx_3, $$where $\mathcal P=\{\sum_jx_j=0,\ |x_j|\le1/2\}$ and $x_4=-x_1-x_2-x_3$. The measure here is coordinate measure, not Euclidean surface measure. Homogeneity removes the weight with factor $1/(K+4)$. The change
$$ 2x=(u+v+w,u-v-w,-u+v-w,-u-v+w) $$maps $\mathcal P$ onto $|u|+|v|+|w|\le1$ with coordinate Jacobian $1/2$. Radial integration against $e^{-|u|-|v|-|w|}$ proves (1). In particular $H(0,0,0,0)=1/2$.
2. A parity identity for the generating function. The moment-generating function of $Y$ is
$$ F(a,b,c,d)=\frac1{[1-(a+b-c-d)^2][1-(a-b+c-d)^2][1-(a-b-c+d)^2]}. $$Let $F_0$ be its all-even parity component, $F_4$ its all-odd component, and $F_{12}$ the component with $a,b$ odd and $c,d$ even. Let $B=1-a^2-b^2-c^2-d^2$. Then the exact formal identity is
$$ F_{12}=-\frac2B\bigl(abF_0+cdF_4\bigr). \tag{2} $$For a short verification, write $h_0=a+b+c+d$ and $h_1,h_2,h_3$ for the three linear forms in $F$, and set $g_j=h_0-2t_j$, $(t_1,t_2,t_3,t_4)=(a,b,c,d)$. Put $D_H=\prod_{j=0}^3(1-h_j^2)$ and $D_G=\prod_{j=1}^4(1-g_j^2)$. Averaging the eight coordinate sign choices modulo global reversal gives
$$ F_0=\frac B2(D_H^{-1}+D_G^{-1}),\qquad F_4=\frac B2(D_H^{-1}-D_G^{-1}), $$$$ F_{12}=-ab(D_H^{-1}+D_G^{-1})-cd(D_H^{-1}-D_G^{-1}). $$The first two follow from $\sum h_j^2=\sum g_j^2=4\sum t_j^2$; the signed numerators for the third are $-8(ab+cd)$ and $-8ab+8cd$. These prove (2). All denominators have constant term one. Permutation symmetry gives the other five two-odd identities.
3. Strict simultaneous induction. Every all-even coefficient of $F$ is strictly positive: it is a nonnegative, nonzero Laplace moment divided by factorials. Induct on even total degree $K$. Since $1/B$ has nonnegative coefficients, (2) makes every two-odd coefficient of degree $K$ strictly negative using the already-positive four-odd coefficients of degrees at most $K-2$. The $abF_0$ contribution is strictly positive at every permitted exponent, so no cancellation can yield zero.
Next, $\sum Y_j=0$ implies $(\partial_a+\partial_b+\partial_c+\partial_d)F=0$. If $(r,s,t,u)$ are all odd, comparison of the coefficient at $(r-1,s,t,u)$ gives
$$ r c_{r,s,t,u}=-(s+1)c_{r-1,s+1,t,u}-(t+1)c_{r-1,s,t+1,u}-(u+1)c_{r-1,s,t,u+1}. $$All three right-hand coefficients are two-odd, at the same degree, and have just been proved negative. Hence every four-odd coefficient is strictly positive. The induction starts with two-odd degree 2; four-odd terms begin at degree 4. It is not circular: the two-odd step uses lower-degree four-odd terms, and the four-odd step uses current-degree two-odd terms.
Thus the moment in (1) has sign $(-1)^{r/2}$, where $r\in\{0,2,4\}$ counts odd derivative orders. Multiplying by $i^K$ proves the stated rule.
I checked the octahedron normalization by independent exact polynomial integration in six prescribed cases, reproducing the source's constants, including $H(4,1,1,0)=1/40320$ and $H(3,3,1,1)=19/1774080$. A separate exact symbolic calculation averaged all 16 sign substitutions directly and verified (2) without inserting the displayed parity formulas. These are algebra checks; the all-order claim rests on the proof above.
The imported arithmetic input is entirely Bui–Hall's moment theorem. The parity recurrence is a distinct proof step; the Laplace representation and sign conclusion are shared with Orchard and carry no priority claim. The sign proof displayed here concerns fixed derivative orders. The separate uniform filtered extensions are stated in the published version linked above; neither result gives the pointwise Laguerre hierarchy.