Prime Number Theorem And ...

5 Third Approach

5.1 Hadamard factorization

In this file, we prove the Hadamard Factorization theorem for functions of finite order, and prove that the zeta function is such.

5.2 Hoffstein-Lockhart

In this file, we use the Hoffstein-Lockhart construction to prove a zero-free region for zeta.

Hoffstein-Lockhart + Goldfeld-Hoffstein-Liemann

Instead of the “slick” identity \(3+4\cos \theta +\cos 2\theta =2(\cos \theta +1)^2\ge 0\), we use the following more robust identity.

Theorem 5.2.1

For any \(p{\gt}0\) and \(t\in \mathbb {R}\),

\[ 3+p^{2it}+p^{-2it}+2p^{it}+2p^{-it} \ge 0. \]
Proof ▶

This follows immediately from the identity

\[ |1+p^{it}+p^{-it}|^2=1+p^{2it}+p^{-2it}+2p^{it}+2p^{-it}+2. \]

[Note: identities of this type will work in much greater generality, especially for higher degree \(L\)-functions.]

This means that, for fixed \(t\), we define the following alternate function.

Definition 5.2.1
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For \(\sigma {\gt}1\) and \(t\in \mathbb {R}\), define

\[ F(\sigma ) := \zeta ^3(\sigma )\zeta ^2(\sigma +it)\zeta ^2(\sigma -it)\zeta (\sigma +2it)\zeta (\sigma -2it). \]
Theorem 5.2.2

Then \(F\) is real-valued, and whence \(F(\sigma )\ge 1\) there.

Proof ▶

That \(\log F(\sigma )\ge 0\) for \(\sigma {\gt}1\) follows from Theorem 5.2.1.

[Note: I often prefer to avoid taking logs of functions that, even if real-valued, have to be justified as being such. Instead, I like to start with “logF” as a convergent Dirichlet series, show that it is real-valued and non-negative, and then exponentiate...]

From this and Hadamard factorization, we deduce the following.

Theorem 5.2.3

There is a constant \(c{\gt}0\), so that \(\zeta (s)\) does not vanish in the region \(\sigma {\gt}1-\frac{c}{\log t}\), and moreover,

\[ -\frac{\zeta '}{\zeta }(\sigma +it) \ll (\log t)^2 \]

there.

Proof ▶

Use Theorem 5.2.2 and Hadamard factorization.

This allows us to quantify precisely the relationship between \(T\) and \(\delta \) in Theorem 4.4.25....

5.3 Strong PNT

Lemma 5.3.1 AnalyticOn.norm-le-of-norm-le-on-sphere
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An application of the Maximum modulus principle.

Proof ▶

This is standard in the literature.

Theorem 5.3.1 borelCaratheodory’
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An application of

      Complex.borelCaratheodory_zero.
    
Proof ▶

This is standard in the literature.

This upstreamed from https://github.com/math-inc/strongpnt/tree/main

Lemma 5.3.2 cauchy-formula-deriv
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Let \(f\) be analytic on \(|z|\leq R\). For any \(z\) with \(|z|\leq r\) and any \(r'\) with \(0 {\lt} r {\lt} r' {\lt} R\) we have

\[ f'(z)=\frac{1}{2\pi i}\oint _{|w|=r'}\frac{f(w)}{(w-z)^2}\, dw=\frac{1}{2\pi } \int _0^{2\pi }\frac{r'e^{it}\, f(r'e^{it})}{(r'e^{it}-z)^2}\, dt. \]
Proof ▶

This is just Cauchy’s integral formula for derivatives.

Lemma 5.3.3 DerivativeBound
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Let \(R,\, M{\gt}0\) and \(0 {\lt} r {\lt} r' {\lt} R\). Let \(f\) be analytic on \(|z|\leq R\) such that \(f(0)=0\) and suppose \(\Re f(z)\leq M\) for all \(|z|\leq R\). Then we have that

\[ |f'(z)|\leq \frac{2M(r')^2}{(R-r')(r'-r)^2} \]

for all \(|z|\leq r\).

Proof ▶

By Lemma 5.3.2 we know that

\[ f'(z)=\frac{1}{2\pi i}\oint _{|w|=r'}\frac{f(w)}{(w-z)^2}\, dw =\frac{1}{2\pi }\int _0^{2\pi }\frac{r'e^{it}\, f(r'e^{it})}{(r'e^{it}-z)^2}\, dt. \]

Thus,

\begin{equation} \label{pickupPoint1} |f'(z)|=\left|\frac{1}{2\pi }\int _0^{2\pi } \frac{r'e^{it}\, f(r'e^{it})}{(r'e^{it}-z)^2}\, dt\right| \leq \frac{1}{2\pi }\int _0^{2\pi } \left|\frac{r'e^{it}\, f(r'e^{it})}{(r'e^{it}-z)^2}\right|\, dt. \end{equation}
1

Now applying Theorem 5.3.1, and noting that \(r'-r\leq |r'e^{it}-z|\), we have that

\[ \left|\frac{r'e^{it}\, f(r'e^{it})}{(r'e^{it}-z)^2}\right| \leq \frac{2M(r')^2}{(R-r')(r'-r)^2}. \]

Substituting this into Equation (1) and evaluating the integral completes the proof.

Theorem 5.3.2 BorelCaratheodoryDeriv
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Let \(R,\, M{\gt}0\). Let \(f\) be analytic on \(|z|\leq R\) such that \(f(0)=0\) and suppose \(\Re f(z)\leq M\) for all \(|z|\leq R\). Then for any \(0 {\lt} r {\lt} R\),

\[ |f'(z)|\leq \frac{16MR^2}{(R-r)^3} \]

for all \(|z|\leq r\).

Proof ▶

Using Lemma 5.3.3 with \(r'=(R+r)/2\), and noting that \(r {\lt} R\), we have that

\[ |f'(z)|\leq \frac{4M(R+r)^2}{(R-r)^3}\leq \frac{16MR^2}{(R-r)^3}. \]
Definition 5.3.1 TaxicabIntegral
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Let \(0 {\lt} R\). Let \(f:\overline{\mathbb {D}_R}\to \mathbb {C}\) be analytic on neighborhoods of points in \(\overline{\mathbb {D}_R}\). Define the functon \(I_f:\mathbb {D}_R\to \mathbb {C}\) by

\[ I_f(z)=z\int _0^1f(tz)\, dt. \]
Theorem 5.3.3 LogOfAnalyticFunction
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Let \(0{\lt}r{\lt}R\). Let \(B:\overline{\mathbb {D}_{R}}\to \mathbb {C}\) be analytic on neighborhoods of points in \(\overline{\mathbb {D}_{R}}\) with \(B(z)\neq 0\) for all \(z\in \overline{\mathbb {D}_{R}}\).Then there exists \(J_B:\mathbb {D}_R\to \mathbb {C}\) that is analytic on neighborhoods of points in \(\mathbb {D}_R\) such that

  • \(J_B(0)=0\)

  • \(J_B'(z)=B'(z)/B(z)\) for all \(z\in \overline{\mathbb {D}_r}\)

  • \(\log |B(z)|-\log |B(0)|=\mathfrak {R}J_B(z)\) for all \(z\in \mathbb {D}_R\).

Proof ▶

We let \(J_B(z)=I_{B'/B}(z)\). Then clearly, \(J_B(0)=0\). Now note that

\begin{align*} I_{B'/B}(z)=z\int _0^1(B’/B)(tz)\, dt=\int _0^z(B’/B)(u)\, du. \end{align*}

Thus by the fundamental theorem of calculus we have that \(J_B'(z)=B'(z)/B(z)\). Now let \(H(z)=\exp (J_B(z))/B(z)\) and note that

\[ H'(z)=(B(z)\, J_B'(z)-B'(z))\left(\frac{\exp (J_B(z))}{(B(z))^2}\right). \]

Thus, \(H\) is constant since we know that \(B(z)\, J_B'(z)-B'(z)=0\) from \(J_B'(z)=B'(z)/B(z)\). So since \(H(0)=\exp (J_B(0))/B(0)=1/B(0)\) we know \(H(z)=1/B(0)\) for all \(z\). So we have,

\[ \frac{1}{B(0)}=\frac{\exp (J_B(z))}{B(z)}\implies \left|\frac{B(z)}{B(0)}\right| =\exp (\mathfrak {R}J_B(z)). \]

Taking the logarithm of both sides completes the proof.

Theorem 5.3.4 LogOfAnalyticFunction’
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A wrapper of the above theorem that will be useful later on.

Proof ▶

See above.

Definition 5.3.2 SetOfZeros
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Let \(R{\gt}0\) and \(f:\mathbb {C}\to \mathbb {C}\). Define the set of zeros \(\mathcal{K}_f(R)=\{ \rho \in \mathbb {C}:|\rho |\leq R,\, f(\rho )=0\} \).

Definition 5.3.3 ZeroOrder
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Let \(f:\mathbb {C}\to \mathbb {C}\). We define \(m_f(\rho )\) as the order of the zero \(\rho \) w.r.t \(f\).

In LEAN, this corresponds exactly with analyticOrderAt/analyticOrderNatAt.

Definition 5.3.4 ZeroFactor
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Let \(f:\mathbb {C}\to \mathbb {C}\) and \(\rho \in \mathbb {C}\). Then there exists \(h_\rho \) such that

\[ f(z)=(z-\rho )^{m_f(\rho )}\, h_\rho (z). \]

In LEAN, this corresponds exactly with (-.analyticOrderAt-ne-top.mp -).choose, but this serves as a wrapper of that with the necessary conditions.

Lemma 5.3.4 ZeroFactorization
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Let \(f:\mathbb {C}\to \mathbb {C}\) be analytic on \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). For all \(\rho \in \mathcal{K}_f(R)\) with \(R{\lt}1\) there exists \(h_\rho (z)\) such that \(h_\rho (z)\) is analytic at \(\rho \), \(h_\rho (\rho )\neq 0\), and \(f(z)=(z-\rho )^{m_f(\rho )}\, h_\rho (z)\).

Proof ▶

Since \(f\) is analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) we know that there exists a series expansion about \(\rho \):

\[ f(z)=\sum _{0\leq n}a_n\, (z-\rho )^n. \]

Now if we let \(m\) be the smallest number such that \(a_m\neq 0\), then

\[ f(z)=\sum _{0\leq n}a_n\, (z-\rho )^n=\sum _{m\leq n}a_n\, (z-\rho )^n =(z-\rho )^m\sum _{m\leq n}a_n\, (z-\rho )^{n-m}=(z-\rho )^m\, h_\rho (z). \]

Trivially, \(h_\rho (z)\) is analytic at \(\rho \) (we have written down the series expansion); now note that

\[ h_\rho (\rho )=\sum _{m\leq n}a_n(\rho -\rho )^{n-m}=\sum _{m\leq n}a_n0^{n-m}=a_m\neq 0. \]
Definition 5.3.5 CFunction
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Let \(0 {\lt} r {\lt} 1\), and \(f:\mathbb {C}\to \mathbb {C}\) be analytic on \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). We define a function \(C_f:\mathbb {C}\to \mathbb {C}\) as follows. This function is constructed by dividing \(f(z)\) by a polynomial whose roots are the zeros of \(f\) inside \(\overline{\mathbb {D}_r}\).

\[ C_f(z)=\begin{cases} \displaystyle \frac{f(z)}{\prod _{\rho \in \mathcal{K}_f(r)}(z-\rho )^{m_f(\rho )}} \qquad \text{for }z\not\in \mathcal{K}_f(r) \\ \displaystyle \frac{h_z(z)}{\prod _{\rho \in \mathcal{K}_f(r)\setminus \{ z\} } (z-\rho )^{m_f(\rho )}}\qquad \text{for }z\in \mathcal{K}_f(r) \end{cases} \]

where \(h_z(z)\) comes from Lemma 5.3.4.

Lemma 5.3.5 CfAnalytic
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If \(f:\mathbb {C}\to \mathbb {C}\) is analytic on \(\overline{\mathbb {D}_1}\) then so too is \(C_f\).

Proof ▶

Look at the definition of \(C_f\) and apply ZeroFactorization.

Definition 5.3.6 BlaschkeB
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Let \(0 {\lt} r {\lt} R {\lt} 1\), and \(f:\mathbb {C}\to \mathbb {C}\) be analytic \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). We define a function \(B_f:\mathbb {C}\to \mathbb {C}\) as follows.

\[ B_f(z)=C_f(z)\prod _{\rho \in \mathcal{K}_f(r)} \left(R-\frac{z\overline{\rho }}{R}\right)^{m_f(\rho )} \]
Lemma 5.3.6 BlaschkeAnalytic
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If \(f:\mathbb {C}\to \mathbb {C}\) is analytic on \(\overline{\mathbb {D}_R}\) then so too is \(B_f\).

Proof ▶

Expand out \(B_f\) as a product, and observe that each part is analytic on \(\overline{\mathbb {D}_R}\).

Lemma 5.3.7 BlaschkeOfZero
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Let \(0 {\lt} r {\lt} R{\lt}1\), and \(f:\mathbb {C}\to \mathbb {C}\) be analytic on \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). Then

\[ |B_f(0)|=|f(0)|\prod _{\rho \in \mathcal{K}_f(r)} \left(\frac{R}{|\rho |}\right)^{m_f(\rho )}. \]
Proof ▶

Since \(f(0)\neq 0\), we know that \(0\not\in \mathcal{K}_f(r)\). Thus,

\[ C_f(0)=\frac{f(0)}{\displaystyle \prod _{\rho \in \mathcal{K}_f(r)}(-\rho )^{m_f(\rho )}}. \]

Thus, substituting this into Definition 5.3.6,

\[ |B_f(0)|=|C_f(0)|\prod _{\rho \in \mathcal{K}_f(r)}R^{m_f(\rho )} =|f(0)|\prod _{\rho \in \mathcal{K}_f(r)}\left(\frac{R}{|\rho |}\right)^{m_f(\rho )}. \]
Lemma 5.3.8 norm-fOfZero-le-norm-BlaschkeOfZero
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Let \(0 {\lt} r {\lt} R{\lt}1\), and \(f:\mathbb {C}\to \mathbb {C}\) be analytic on \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). Then

\[ |f(0)|\leq |B_f(0)|. \]
Proof ▶

Applying lemma 5.3.7 we know that

\[ |B_f(0)|=|f(0)|\prod _{\rho \in \mathcal{K}_f(r)} \left(\frac{R}{|\rho |}\right)^{m_f(\rho )}. \]

Note that for all \(\rho \in \mathcal{K}_f(r)\) that \(1{\lt}R/|\rho |\) since \(r{\lt}R\). Thus, the result follows.

Lemma 5.3.9 DiskBound
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Let \(0 {\lt} r {\lt} R{\lt}1\). If \(f:\mathbb {C}\to \mathbb {C}\) is a function analytic on \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\) such that \(|f(z)|\leq B\) for \(|z|\leq R\), then \(|B_f(z)|\leq B\) for \(|z|\leq R\) also.

Proof ▶

For \(|z|=R\), we know that \(z\not\in \mathcal{K}_f(r)\). Thus,

\[ C_f(z)=\frac{f(z)}{\displaystyle \prod _{\rho \in \mathcal{K}_f(r)}(z-\rho )^{m_f(\rho )}}. \]

Thus, substituting this into Definition 5.3.6,

\[ |B_f(z)|=|f(z)|\prod _{\rho \in \mathcal{K}_f(r)} \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|^{m_f(\rho )}. \]

But note that

\[ \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right| =\frac{|R^2-z\overline{\rho }|/R}{|z-\rho |} =\frac{|z|\cdot |\overline{z-\rho }|/R}{|z-\rho |}=1. \]

So we have that \(|B_f(z)|=|f(z)|\leq B\) when \(|z|=R\). Now by the maximum modulus principle, we know that the maximum of \(|B_f|\) must occur on the boundary where \(|z|=R\). Thus \(|B_f(z)|\leq B\) for all \(|z|\leq R\).

Lemma 5.3.10 BlaschkeNonZero
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Let \(0 {\lt} r {\lt} R{\lt}1\) and \(f:\overline{\mathbb {D}_1}\to \mathbb {C}\) be analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) with \(f(0)\neq 0\). Then \(B_f(z)\neq 0\) for all \(z\in \overline{\mathbb {D}_r}\).

Proof ▶

Suppose that \(z\in \mathcal{K}_f(r)\). Then we have that

\[ C_f(z)=\frac{h_z(z)}{\displaystyle \prod _{\rho \in \mathcal{K}_f(r)\setminus \{ z\} } (z-\rho )^{m_f(\rho )}}. \]

where \(h_z(z)\neq 0\) according to Lemma 5.3.4. Thus, substituting this into Definition 5.3.6,

\begin{equation} \label{pickupPoint2} |B_f(z)|=|h_z(z)|\cdot \left|R-\frac{|z|^2}{R}\right|^{m_f(z)} \prod _{\rho \in \mathcal{K}_f(r)\setminus \{ z\} } \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|^{m_f(\rho )}. \end{equation}
4

Trivially, \(|h_z(z)|\neq 0\). Now note that

\[ \left|R-\frac{|z|^2}{R}\right|=0\implies |z|=R. \]

However, this is a contradiction because \(z\in \overline{\mathbb {D}_r}\) tells us that \(|z|\leq r {\lt} R\). Similarly, note that

\[ \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|=0\implies |z|=\frac{R^2}{|\overline{\rho }|}. \]

However, this is also a contradiction because \(\rho \in \mathcal{K}_f(r)\) tells us that \(R {\lt} R^2/|\overline{\rho }|=|z|\), but \(z\in \overline{\mathbb {D}_r}\) tells us that \(|z|\leq r {\lt} R\). So, we know that

\[ \left|R-\frac{|z|^2}{R}\right|\neq 0\qquad \text{and}\qquad \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|\neq 0 \quad \text{for all}\quad \rho \in \mathcal{K}_f(r)\setminus \{ z\} . \]

Applying this to Equation (4) we have that \(|B_f(z)|\neq 0\). So, \(B_f(z)\neq 0\).

Now suppose that \(z\not\in \mathcal{K}_f(r)\). Then we have that

\[ C_f(z)=\frac{f(z)}{\displaystyle \prod _{\rho \in \mathcal{K}_f(r)}(z-\rho )^{m_f(\rho )}}. \]

Thus, substituting this into Definition 5.3.6,

\begin{equation} \label{pickupPoint3} |B_f(z)|=|f(z)|\prod _{\rho \in \mathcal{K}_f(r)} \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|^{m_f(\rho )}. \end{equation}
5

We know that \(|f(z)|\neq 0\) since \(z\not\in \mathcal{K}_f(r)\). Now note that

\[ \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|=0\implies |z|=\frac{R^2}{|\overline{\rho }|}. \]

However, this is a contradiction because \(\rho \in \mathcal{K}_f(r)\) tells us that \(R {\lt} R^2/|\overline{\rho }|=|z|\), but \(z\in \overline{\mathbb {D}_r}\) tells us that \(|z|\leq r {\lt} R\). So, we know that

\[ \left|\frac{R-z\overline{\rho }/R}{z-\rho }\right|\neq 0 \quad \text{for all}\quad \rho \in \mathcal{K}_f(r). \]

Applying this to Equation (5) we have that \(|B_f(z)|\neq 0\). So, \(B_f(z)\neq 0\).

We have shown that \(B_f(z)\neq 0\) for both \(z\in \mathcal{K}_f(r)\) and \(z\not\in \mathcal{K}_f(r)\), so the result follows.

Theorem 5.3.5 ZerosBound
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Let \(0{\lt} r {\lt} R{\lt}1\). If \(f:\mathbb {C}\to \mathbb {C}\) is a function analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) with \(f(0)=1\) and \(|f(z)|\leq B\) for \(|z|\leq R\), then

\[ \sum _{\rho \in \mathcal{K}_f(r)}m_f(\rho )\leq \frac{\log B}{\log (R/r)}. \]
Proof ▶

Since \(f(0)=1\), by Lemma 5.3.7 we know that

\[ |B_f(0)| =|f(0)|\prod _{\rho \in \mathcal{K}_f(r)}\left(\frac{R}{|\rho |}\right)^{m_f(\rho )} =\prod _{\rho \in \mathcal{K}_f(r)}\left(\frac{R}{|\rho |}\right)^{m_f(\rho )}. \]

Thus, substituting this into Definition 5.3.6,

\[ (R/r)^{\sum _{\rho \in \mathcal{K}_f(r)}m_f(\rho )} =\prod _{\rho \in \mathcal{K}_f(r)}\left(\frac{R}{r}\right)^{m_f(\rho )} \leq \prod _{\rho \in \mathcal{K}_f(r)}\left(\frac{R}{|\rho |}\right)^{m_f(\rho )} =|B_f(0)|\leq B \]

whereby Lemma 5.3.9 we know that \(|B_f(z)|\leq B\) for all \(|z|\leq R\). Taking the logarithm of both sides and rearranging gives the desired result.

Definition 5.3.7 JBlaschke
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Let \(0 {\lt} r {\lt} R{\lt}1\). If \(f:\mathbb {C}\to \mathbb {C}\) is a function analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) with \(f(0)=1\), define \(L_f(z)=J_{B_f}(z)\) where \(J\) is from Theorem 5.3.3 and \(B_f\) is from Definition 5.3.6.

Let \(B{\gt}1\) and \(0 {\lt} r' {\lt} r {\lt} R{\lt}1\). If \(f:\mathbb {C}\to \mathbb {C}\) is a function analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) with \(f(0)=1\) and \(|f(z)|\leq B\) for all \(|z|\leq R\), then for all \(|z|\leq r'\)

\[ |L_f'(z)|\leq \frac{16\log (B)\, r^2}{(r-r')^3}. \]
Proof ▶

By Lemma 5.3.9 we immediately know that \(|B_f(z)|\leq B\) for all \(|z|\leq R\). Now since \(L_f=J_{B_f}\) by Definition 5.3.7, by Theorem 5.3.3 we know that

\[ L_f(0)=0\qquad \text{and}\qquad \Re L_f(z)=\log |B_f(z)|-\log |B_f(0)|\leq \log |B_f(z)|\leq \log B \]

for all \(|z|\leq r\). Note that in the above

\[ 0=\log |f(0)|\leq \log |B_f(0)| \]

because of Lemma 5.3.8. So by Theorem 5.3.2, it follows that

\[ |L_f'(z)|\leq \frac{16\log (B)\, r^2}{(r-r')^3} \]

for all \(|z|\leq r'\).

Let \(B{\gt}1\) and \(0 {\lt} r' {\lt} r {\lt} R' {\lt} R{\lt}1\). If \(f:\mathbb {C}\to \mathbb {C}\) is a function analytic on neighborhoods of points in \(\overline{\mathbb {D}_1}\) with \(f(0)=1\) and \(|f(z)|\leq B\) for all \(|z|\leq R\), then for all \(z\in \overline{\mathbb {D}_{r'}}\setminus \mathcal{K}_f(R')\) we have

\[ \left|\frac{f'}{f}(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho }\right| \leq \left(\frac{16r^2}{(r-r')^3}+\frac{1}{(R^2/R'-R')\, \log (R/R')}\right)\log B. \]
Proof ▶

Since \(z\in \overline{\mathbb {D}_{r'}}\setminus \mathcal{K}_f(R')\) we know that \(z\not\in \mathcal{K}_f(R')\); thus, by Definition 5.3.5 we know that

\[ C_f(z)=\frac{f(z)}{\displaystyle \prod _{\rho \in \mathcal{K}_f(r)}(z-\rho )^{m_f(\rho )}}. \]

Substituting this into Definition 5.3.6 we have that

\[ B_f(z)=f(z)\prod _{\rho \in \mathcal{K}_f(r)} \left(\frac{R-z\overline{\rho }/R}{z-\rho }\right)^{m_f(\rho )}. \]

Taking the complex logarithm of both sides we have that

\[ \mathrm{Log}\, B_f(z)=\mathrm{Log}\, f(z) +\sum _{\rho \in \mathcal{K}_f(r)}m_f(\rho )\, \mathrm{Log}(R-z\overline{\rho }/R) -\sum _{\rho \in \mathcal{K}_f(r)}m_f(\rho )\, \mathrm{Log}(z-\rho ). \]

Taking the derivative of both sides we have that

\[ \frac{B_f'}{B_f}(z)=\frac{f'}{f}(z) +\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-R^2/\overline{\rho }} -\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho }. \]

By Definition 5.3.7 and Theorem 5.3.3, since \(L_f(z)=J_{B_f}(z)\) we have \(L_f'(z)=J'_{B_f}(z)=(B_f'/B_f)(z)\). Thus,

\[ \frac{f'}{f}(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho } =L_f'(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-R^2/\overline{\rho }}. \]

Now since \(z\in \overline{\mathbb {D}_{r'}}\subseteq \overline{\mathbb {D}_{R'}}\) and \(\rho \in \mathcal{K}_f(r)\subseteq \mathcal{K}_f(R')\), we know that \(R^2/R'-R'\leq |z-R^2/\overline{\rho }|\). Thus by the triangle inequality we have

\[ \left|\frac{f'}{f}(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho }\right| \leq |L_f'(z)|+\left(\frac{1}{R^2/R'-R'}\right)\sum _{\rho \in \mathcal{K}_f(r)}m_f(\rho ). \]

Now by Theorem 5.3.5 and 5.3.6 we get our desired result with a little algebraic manipulation.

Theorem 5.3.8 ZetaFixedLowerBound
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For all \(t\in \mathbb {R}\) one has

\[ |\zeta (3/2+it)|\geq \frac{\zeta (3)}{\zeta (3/2)}. \]
Proof ▶

From the Euler product expansion of \(\zeta \), we have that for \(\Re s{\gt}1\)

\[ \zeta (s)=\prod _p\frac{1}{1-p^{-s}}. \]

Thus, we have that

\[ \frac{\zeta (2s)}{\zeta (s)}=\prod _p\frac{1-p^{-s}}{1-p^{-2s}}=\prod _p\frac{1}{1+p^{-s}}. \]

Now note that \(|1-p^{-(3/2+it)}|\leq 1+|p^{-(3/2+it)}|=1+p^{-3/2}\). Thus,

\[ |\zeta (3/2+it)|=\prod _p\frac{1}{|1-p^{-(3/2+it)}|} \geq \prod _p\frac{1}{1+p^{-3/2}}=\frac{\zeta (3)}{\zeta (3/2)} \]

for all \(t\in \mathbb {R}\) as desired.

Definition 5.3.8 riemannZeta1
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Let

\[ \zeta _1(s)=1+\frac{1}{s-1}-s\int _1^\infty \{ x\} \, x^{-s}\, \frac{dx}{x}. \]
Theorem 5.3.9 Zeta1AltFormula
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We have that

\[ \zeta _1(s)=\zeta _0(1,s) \]

where \(\zeta _0(1,s)\) comes from Definition 4.4.1.

Proof ▶

Note that

\[ \zeta _0(1,s)=1+\frac{-1}{1-s}+\frac{-1}{2}+ s\int _1^\infty \frac{\lfloor x\rfloor +1/2-x}{x^{s+1}}\, dx. \]

With minor simplifications we have

\[ \zeta _0(1,s)=1+\frac{1}{s-1}-\frac{1}{2}+ \frac{s}{2}\int _1^\infty x^{-s-1}\, dx-s\int _1^\infty \{ x\} \, x^{-s-1}\, dx. \]

The first integral evaluates to \(1/s\) (when \(0{\lt}\mathfrak {R}s\)), so this term when multiplied by the \(s/2\) cancels with the \(-1/2\). This exactly gives \(\zeta _1\).

Theorem 5.3.10 ZetaAltFormula
✓

We have that

\[ \zeta (s)=\zeta _1(s) \]

for all \(s\in S\) with \(S=\{ s\in \mathbb {C}:0{\lt}\mathfrak {R}s,\, s\neq 1\} \).

Proof ▶

This immediately follows from Lemmas 5.3.9 and 4.4.9.

Theorem 5.3.11 GlobalBound
✓
#

For all \(s\in \mathbb {C}\) with \(|s|\leq 1\) and \(t\in \mathbb {R}\) with \(|t|\geq 2\), we have that

\[ |\zeta (s+3/2+it)|\leq 7+2\, |t|. \]
Proof ▶

For the sake of clearer proof writing let \(z=s+3/2+it\). Since \(|s|\leq 1\) we know that \(1/2\leq \mathfrak {R}z\); additionally, as \(|t|\geq 2\), we know \(1\leq |\mathfrak {I}z|\). So, \(z\in S\). Thus, from Lemma 5.3.10 we know that

\[ |\zeta (z)|\leq 1+\frac{1}{|z-1|} +|z|\cdot \left|\int _1^\infty \{ x\} \, x^{-z}\, \frac{dx}{x}\right| \]

by applying the triangle inequality. Now note that \(|z-1|\geq 1\). Likewise,

\[ |z|\cdot \left|\int _1^\infty \{ x\} \, x^{-z}\, \frac{dx}{x}\right| \leq |z|\int _1^\infty |\{ x\} \, x^{-z-1}|\, dx \leq |z|\int _1^\infty x^{-\Re z-1}\, dx=\frac{|z|}{\Re z}\leq 2\, |z|. \]

Thus we have that,

\[ |\zeta (s+3/2+it)|=|\zeta (z)|\leq 1+1+2\, |z|=2+2\, |s+3/2+it| \leq 2+2\, |s|+3+2\, |it|\leq 7+2\, |t|. \]
Theorem 5.3.12 norm-zeta-strict-mono-ofReal
✓
#

If \(a,b\in \mathbb {R}\) with \(1{\lt}b{\lt}a\), then

\[ |\zeta (a)|{\lt}|\zeta (b)|. \]
Proof ▶

Expand out \(\zeta \) as a summation (we can do this as we are in the region of convergence) and ignore the norm as every term is positive and real. Comparing term by term proves the result.

Theorem 5.3.13 LogDerivZetaFinalBound
✓

Let \(t\in \mathbb {R}\) with \(|t|\geq 2\) and \(0 {\lt} r' {\lt} r {\lt} R' {\lt} R{\lt}1\). If \(f(z)=\zeta (z+3/2+it)\), then for all \(z\in \overline{\mathbb {D}_{r'}}\setminus \mathcal{K}_f(R')\) we have that

\[ \left|\frac{f'}{f}(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho }\right| \ll \left(\frac{16r^2}{(r-r')^3}+\frac{1}{(R^2/R'-R')\, \log (R/R')}\right)\log |t|. \]
Proof ▶

Let \(g(z)=\zeta (z+3/2+it)/\zeta (3/2+it)\). Note that \(g(0)=1\) and for \(|z|\leq R\)

\[ |g(z)|=\frac{|\zeta (z+3/2+it)|}{|\zeta (3/2+it)|} \leq \frac{\zeta (3/2)}{\zeta (3)}\cdot (7+2\, |t|)\leq \frac{13\, \zeta (3/2)}{3\, \zeta (3)}\, |t| \]

by Theorems 5.3.8 and 5.3.11. Thus by Theorem 5.3.7 we have that

\[ \left|\frac{g'}{g}(z)-\sum _{\rho \in \mathcal{K}_g(r)}\frac{m_g(\rho )}{z-\rho }\right| \leq \left(\frac{16r^2}{(r-r')^3}+\frac{1}{(R^2/R'-R')\, \log (R/R')}\right) \left(\log |t|+\log \left(\frac{13\, \zeta (3/2)}{3\, \zeta (3)}\right)\right). \]

Now note that \(f'/f=g'/g\), \(\mathcal{K}_f(r)=\mathcal{K}_g(r)\), and \(m_g(\rho )=m_f(\rho )\) for all \(\rho \in \mathcal{K}_f(r)\). Thus we have that,

\[ \left|\frac{f'}{f}(z)-\sum _{\rho \in \mathcal{K}_f(r)}\frac{m_f(\rho )}{z-\rho }\right| \ll \left(\frac{16r^2}{(r-r')^3}+\frac{1}{(R^2/R'-R')\, \log (R/R')}\right)\log |t| \]

where the implied constant \(C\) is taken to be

\[ C\geq 1+\frac{\log (11\, \zeta (3/2)/\zeta (3))}{\log 2}. \]
Theorem 5.3.14 ZetaShiftFiniteZeros
✓
#

For all \(|t|\geq 2\), if \(f(z)=\zeta (z+3/2+it)\), then \(f(z)\) has a finite number of zeros in \(\overline{\mathbb {D}_1}\).

Proof ▶

If we suppose the opposite, i.e. that there are an infinite number of zeros in this region, then \(f\equiv 0\) by the identity theorem. This is a contradiction, so the statement must be true.

Definition 5.3.9 ZeroWindow
✓
#

Let \(\mathcal{Z}_t=\{ \rho \in \mathbb {C}:\zeta (\rho )=0,\, |\rho -(3/2+it)|\leq 3/4\} \).

Theorem 5.3.15 SumBoundI
✓

For all \(\delta \in (0,1)\) and \(t\in \mathbb {R}\) with \(|t|\geq 2\) we have

\[ \left|\frac{\zeta '}{\zeta }(1+\delta +it) -\sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{1+\delta +it-\rho }\right|\ll \log |t|. \]
Proof ▶

We apply Theorem 5.3.13 where \(r'=2/3\), \(r=3/4\), \(R'=4/5\), and \(R=5/6\). Thus, for all \(z\in \overline{\mathbb {D}_{2/3}}\setminus \mathcal{K}_f(4/5)\) we have that

\[ \left|\frac{\zeta '}{\zeta }(z+3/2+it) -\sum _{\rho \in \mathcal{K}_f(3/4)}\frac{m_f(\rho )}{z-\rho }\right|\ll \log |t| \]

where \(f(z)=\zeta (z+3/2+it)\) for \(t\in \mathbb {R}\) with \(|t|\geq 2\). Now if we let \(z=-1/2+\delta \), then \(z\in (-1/2,1/2)\subseteq \overline{\mathbb {D}_{2/3}}\). Additionally, \(f(z)=\zeta (1+\delta +it)\), where \(1+\delta +it\) lies in the zero-free region where \(\sigma {\gt}1\). Thus, \(z\not\in \mathcal{K}_f(4/5)\). So,

\[ \left|\frac{\zeta '}{\zeta }(1+\delta +it) -\sum _{\rho \in \mathcal{K}_f(3/4)}\frac{m_f(\rho )}{-1/2+\delta -\rho }\right| \ll \log |t|. \]

But now note that if \(\rho \in \mathcal{K}_f(3/4)\), then \(\zeta (\rho +3/2+it)=0\) and \(|\rho |\leq 3/4\). Thus, \(\rho +3/2+it\in \mathcal{Z}_t\) (the argument works in reverse as well). Additionally, note that \(m_f(\rho )=m_\zeta (\rho +3/2+it)\). So changing variables using these facts gives us that

\[ \left|\frac{\zeta '}{\zeta }(1+\delta +it) -\sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{1+\delta +it-\rho }\right| \ll \log |t|. \]
Theorem 5.3.16 ShiftTwoBound
✓
#

For all \(\delta \in (0,1)\) and \(t\in \mathbb {R}\) with \(|t|\geq 2\) we have

\[ -\Re \left(\frac{\zeta '}{\zeta }(1+\delta +2it)\right)\ll \log |t|. \]
Proof ▶

Note that, for \(\rho \in \mathcal{Z}_{2t}\)

\begin{align*} \Re \left(\frac{1}{1+\delta +2it-\rho }\right) & =\Re \left(\frac{1+\delta -2it-\overline{\rho }}{(1+\delta +2it-\rho )(1+\delta -2it-\overline{\rho })}\right) \\ & =\frac{\Re (1+\delta -2it-\overline{\rho })}{|1+\delta +2it-\rho |^2} =\frac{1+\delta -\Re \rho }{(1+\delta -\Re \rho )^2+(2t-\mathfrak {I}\rho )^2}. \end{align*}

Now since \(\rho \in \mathcal{Z}_{2t}\), we have that \(|\rho -(3/2+2it)|\leq 3/4\). So, we have \(\Re \rho \in [3/4,9/4]\) and \(\mathfrak {I}\rho \in [2t-3/4,2t+3/4]\). Additionally, we know that \(\zeta (\rho )=0\). This implies the stronger condition that \(\Re \rho \in [3/4,1]\). Thus,

\[ \delta \leq 1+\delta -\Re \rho \qquad \text{and}\qquad (1+\delta -\Re \rho )^2+(2t-\mathfrak {I}\rho )^2\leq 25/16+9/16=17/8. \]

Which implies that

\begin{equation} \label{pickupPoint4} 0{\lt}\frac{8}{17}\, \delta \leq \frac{1+\delta -\Re \rho }{(1+\delta -\Re \rho )^2+(2t-\mathfrak {I}\rho )^2} =\Re \left(\frac{1}{1+\delta +2it-\rho }\right). \end{equation}
6

Note that, from Lemma 5.3.15, we have

\[ \sum _{\rho \in \mathcal{Z}_{2t}}m_\zeta (\rho )\, \Re \left(\frac{1}{1+\delta +2it-\rho }\right) -\Re \left(\frac{\zeta '}{\zeta }(1+\delta +2it)\right) \leq \left|\frac{\zeta '}{\zeta }(1+\delta +2it) -\sum _{\rho \in \mathcal{Z}_{2t}}\frac{m_\zeta (\rho )}{1+\delta +2it-\rho }\right| \ll \log |2t|. \]

Since \(m_\zeta (\rho )\geq 0\) for all \(\rho \in \mathcal{Z}_{2t}\), the inequality from Equation (6) tells us that by subtracting the sum from both sides we have

\[ -\Re \left(\frac{\zeta '}{\zeta }(1+\delta +2it)\right)\ll \log |2t|. \]

Noting that \(\log |2t|=\log (2)+\log |t|\leq 2\log |t|\) completes the proof.

Theorem 5.3.17 ShiftOneBound
✓
#

There exists \(C{\gt}0\) such that for all \(\delta \in (0,1)\) and \(t\in \mathbb {R}\) with \(|t|\geq 2\); if \(\zeta (\rho )=0\) with \(\rho =\sigma +it\), then

\[ -\Re \left(\frac{\zeta '}{\zeta }(1+\delta +it)\right) \leq -\frac{1}{1+\delta -\sigma }+C\log |t|. \]
Proof ▶

Note that for \(\rho '\in \mathcal{Z}_t\)

\begin{align*} \mathfrak {R}\left(\frac{1}{1+\delta +it-\rho '}\right)& =\mathfrak {R}\left( \frac{1+\delta -it-\overline{\rho '}}{(1+\delta +it-\rho ')(1+\delta -it-\overline{\rho '})}\right) \\ & =\frac{\mathfrak {R}(1+\delta -it-\overline{\rho '})}{|1+\delta +it-\rho '|^2} =\frac{1+\delta -\mathfrak {R}\rho '}{(1+\delta -\mathfrak {R}\rho ')^2+(t-\mathfrak {I}\rho ')^2}. \end{align*}

Now since \(\rho '\in \mathcal{Z}_t\), we have that \(|\rho '-(3/2+it)|\leq 3/4\). So, we have \(\mathfrak {R}\rho '\in [3/4,9/4]\) and \(\mathfrak {I}\rho '\in [t-3/4,t+3/4]\). Additionally, we know that \(\zeta (\rho ')=0\). This implies the stronger condition that \(\mathfrak {R}\rho '\in [3/4,1]\). Thus,

\[ \delta \leq 1+\delta -\mathfrak {R}\rho ' \qquad \text{and}\qquad (1+\delta -\mathfrak {R}\rho ')^2+(t-\mathfrak {I}\rho ')^2\leq 25/16+9/16=17/8. \]

Which implies that

\begin{equation} \label{pickupPoint5} 0{\lt}\frac{8}{17}\, \delta \leq \frac{1+\delta -\mathfrak {R}\rho '}{(1+\delta -\mathfrak {R}\rho ')^2 +(t-\mathfrak {I}\rho ')^2}=\mathfrak {R}\left(\frac{1}{1+\delta +it-\rho '}\right). \end{equation}
7

Note that, from Lemma 5.3.15, we have

\[ \sum _{\rho '\in \mathcal{Z}_t}m_\zeta (\rho ')\, \mathfrak {R}\left( \frac{1}{1+\delta +it-\rho '}\right)-\mathfrak {R}\left( \frac{\zeta '}{\zeta }(1+\delta +it)\right)\leq \left|\frac{\zeta '}{\zeta }(1+\delta +it) -\sum _{\rho '\in \mathcal{Z}_t}\frac{m_\zeta (\rho ')}{1+\delta +it-\rho '}\right|\ll \log |t|. \]

Now we proceed via cases. If \(\rho \in \mathcal{Z}_t\), then \(\mathcal{Z}_t=\rho \sqcup (\mathcal{Z}_t\setminus \rho )\) and the inequality from Equation (7) tells us that by subtracting the sum over all \(\rho '\in \mathcal{Z}_t\setminus \{ \rho \} \) from both sides we have

\[ \frac{m_\zeta (\rho )}{\mathfrak {R}(1+\delta +it-\rho )} -\mathfrak {R}\left(\frac{\zeta '}{\zeta }(1+\delta +it)\right)\ll \log |t|. \]

But of course we have that \(\mathfrak {R}(1+\delta +it-\rho )=1+\delta -\sigma \). So subtracting this term from both sides and recalling the implied constant we have

\[ -\mathfrak {R}\left(\frac{\zeta '}{\zeta }(1+\delta +it)\right)\leq -\frac{m_\zeta (\rho )}{1+\delta -\sigma }+C\log |t|. \]

We have that \(\sigma \leq 1\) since \(\zeta \) is zero free on the right half plane \(\sigma {\gt}1\). Thus, \(0{\lt}1+\delta -\sigma \). Noting this in combination with the fact that \(1\leq m_\zeta (\rho )\) gives us that

\[ -\mathfrak {R}\left(\frac{\zeta '}{\zeta }(1+\delta +it)\right)\leq -\frac{m_\zeta (\rho )}{1+\delta -\sigma }+C\log |t|\leq -\frac{1}{1+\delta -\rho }+(7+C)\log |t|. \]

Now if \(\rho \not\in \mathcal{Z}_t\), then \(|\sigma -3/2|=|\rho -(3/2+it)|{\gt}3/4\) since \(\zeta (\rho )=0\). Additionally, \(\sigma \leq 1\) since \(\zeta (\rho )=0\), thus \(3/2-\sigma =|\sigma -3/2|{\gt}3/4\). So it follows that

\[ \frac{1}{1+\delta -\sigma }{\lt}4{\lt}7\log 2\leq 7\log |t|. \]

Thus, by subtracting the sum over \(\rho '\in \mathcal{Z}_t\) from both sides we have

\[ -\mathfrak {R}\left(\frac{\zeta '}{\zeta }(1+\delta +it)\right)\leq C\log |t|\leq -\frac{1}{1+\delta -\rho }+(7+C)\log |t|. \]
Theorem 5.3.18 ShiftZeroBound
✓
#

For all \(\delta \in (0,1)\) we have

\[ -\Re \left(\frac{\zeta '}{\zeta }(1+\delta )\right)\leq \frac{1}{\delta }+O(1). \]
Proof ▶

From Theorem 4.4.10 we know that

\[ -\frac{\zeta '}{\zeta }(s)=\frac{1}{s-1}+O(1). \]

Changing variables \(s\mapsto 1+\delta \) and applying the triangle inequality we have that

\[ -\Re \left(\frac{\zeta '}{\zeta }(1+\delta )\right)\leq \left| -\frac{\zeta '}{\zeta }(1+\delta )\right|\leq \frac{1}{\delta }+O(1). \]
Theorem 5.3.19 vonMangoldtLSeriesSummable
✓
#

The series

\[ \sum _{n=1}^\infty \frac{\Lambda (n)}{n^s} \]

converges when \(1{\lt}\mathfrak {R}(s)\).

Proof ▶

We know that \(\Lambda (n)\) is \(O(n^\varepsilon )\) since it is bounded above by \(\log (n)\). Thus,

\[ \left|\sum _{n=1}^\infty \frac{\Lambda (n)}{n^s}\right|\leq \sum _{n=1}^\infty \left|\frac{\Lambda (n)}{n^s}\right|\ll \sum _{n=1}^\infty \frac{1}{n^{\mathfrak {R}(s)-\varepsilon }}. \]

Since \(\varepsilon \) can be arbitrarily small, we know the left hand side converges by the \(p\)-test.

Theorem 5.3.20 ZeroWindowFinite
✓
#

For all \(|t|\geq 2\), \(\mathcal{Z}(t)\) contains a finite number of points.

Proof ▶

If we suppose the opposite, i.e. that there are an infinite number of zeta zeros in this region, then \(\zeta \equiv 0\) by the identity theorem. This is a contradiction, so the statement must be true.

Theorem 5.3.21 ZeroInequality
✓
#

There exists a constant \(0 {\lt} E{\lt}1/14\) such that for all \(\rho =\sigma +it\) with \(\zeta (\rho )=0\) and \(|t|\geq 2\), one has

\[ \sigma \leq 1-\frac{E}{\log |t|}. \]
Proof ▶

From Theorem 4.5.1 when \(\Re s{\gt}1\) we have

\[ -\frac{\zeta '}{\zeta }(s)=\sum _{1\leq n}\frac{\Lambda (n)}{n^s}. \]

Thus,

\[ -3\, \frac{\zeta '}{\zeta }(1+\delta ) -4\, \frac{\zeta '}{\zeta }(1+\delta +it) -\frac{\zeta '}{\zeta }(1+\delta +2it) =\sum _{1\leq n}\Lambda (n)\, n^{-(1+\delta )}\left(3+4n^{-it}+n^{-2it}\right). \]

Now applying Euler’s identity

\begin{align*} -3\, \Re \left(\frac{\zeta '}{\zeta }(1+\delta )\right)& -4\, \Re \left(\frac{\zeta '}{\zeta }(1+\delta +it)\right) -\Re \left(\frac{\zeta '}{\zeta }(1+\delta +2it)\right) \\ & \qquad \qquad \qquad =\sum _{1\leq n}\Lambda (n)\, n^{-(1+\delta )} \left(3+4\cos (-t\log n)+\cos (-2t\log n)\right) \end{align*}

Since

\[ 3+4\cos (-t\log n)+\cos (-2t\log n)=2\, (1+\cos (-t\log n))^2\geq 0, \]

we know that the series on the right hand side is bounded below by \(0\), and by Lemmas 5.3.16, 5.3.17, and 5.3.18 we have an upper bound on the left hand side. So,

\[ 0\leq \frac{3}{\delta }+3A-\frac{4}{1+\delta -\sigma }+4B\log |t|+C\log |t| \]

where \(A\), \(B\), and \(C\) are the implied constants coming from Lemmas 5.3.18, 5.3.17, and 5.3.16 respectively. By choosing \(D\geq 5A+4B+C\geq 3A/\log 2+4B+C\) we have

\[ \frac{4}{1+\delta -\sigma }\leq \frac{3}{\delta }+D\log |t| \]

by some manipulation. Now if we choose \(\delta =(2D\log |t|)^{-1}\) then we have

\[ \frac{4}{1-\sigma +1/(2D\log |t|)}\leq 7D\log |t|. \]

So with some manipulation we have that

\[ \sigma \leq 1-\frac{1}{14D\log |t|}. \]

This is exactly the desired result with the constant \(E=(14D)^{-1}\). Since \(D\geq 5A+4B+C\geq 1\) we have that \(E\in (0,1/14)\).

Definition 5.3.10 DeltaT
✓
#

Let \(\delta _t=E/\log |t|\) where \(E\) is the constant coming from Theorem 5.3.21.

Theorem 5.3.22 DeltaRange
✓
#

For all \(t\in \mathbb {R}\) with \(|t|\geq 2\) we have that

\[ \delta _t{\lt}1/9. \]
Proof ▶

Note that \(\delta _t=E/\log |t|\) where \(E\) is the implied constant from Lemma 5.3.21. But we know that \(E=(14D)^{-1}\) where \(D\geq 5A+4B+C\) where \(A\), \(B\), and \(C\) are the constants coming from Lemmas 5.3.18, 5.3.17, and 5.3.16 respectively. Thus,

\[ E\leq \frac{1}{14\, (5A+4B+C)}. \]

But note that \(A\geq 1\), \(B{\gt}0\), and \(C{\gt}0\) by Lemmas 5.3.18, 5.3.17, and 5.3.16 respectively. So, by a very lazy estimate we have \(E\leq 1/14\). Thus,

\[ \delta _t=\frac{E}{\log |t|}\leq \frac{1}{14\, \log 2}{\lt}\frac{1}{9}. \]

For all \(t\in \mathbb {R}\) with \(|t|\geq 2\) and \(z=\sigma +it\) where \(1-\delta _t/3\leq \sigma \leq 3/2\), we have that

\[ \left|\frac{\zeta '}{\zeta }(z) -\sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{z-\rho }\right|\ll \log |t|. \]
Proof ▶

By Lemma 5.3.22 we have that

\[ -29/54{\lt}-1/2-\delta _t/3\leq \sigma -3/2\leq 0. \]

We apply Theorem 5.3.13 where \(r'=2/3\), \(r=3/4\), \(R'=4/5\), and \(R=5/6\). Thus for all \(z\in \overline{\mathbb {D}_{2/3}}\setminus \mathcal{K}_f(4/5)\) we have that

\[ \left|\frac{\zeta '}{\zeta }(z+3/2+it) -\sum _{\rho \in \mathcal{K}_f(3/4)}\frac{m_f(\rho )}{z-\rho }\right|\ll \log |t| \]

where \(f(z)=\zeta (z+3/2+it)\) for \(t\in \mathbb {R}\) with \(|t|\geq 2\). Now if we let \(z=\sigma -3/2\), then \(z\in (-29/54,0)\subseteq \overline{\mathbb {D}_{2/3}}\). Additionally, \(f(z)=\zeta (\sigma +it)\), where \(\sigma +it\) lies in the zero free region given by Lemma 5.3.21 since \(\sigma \geq 1-\delta _t/3\geq 1-\delta _t\). Thus, \(z\not\in \mathcal{K}_f(4/5)\). So,

\[ \left|\frac{\zeta '}{\zeta }(\sigma +it) -\sum _{\rho \in \mathcal{K}_f(3/4)}\frac{m_f(\rho )}{\sigma -3/2-\rho }\right|\ll \log |t|. \]

But now note that if \(\rho \in \mathcal{K}_f(3/4)\), then \(\zeta (\rho +3/2+it)=0\) and \(|\rho |\leq 3/4\) (and the argument works in reverse). Additionally, note that \(m_f(\rho )=m_\zeta (\rho +3/2+it)\). So changing variables using these facts gives us that

\[ \left|\frac{\zeta '}{\zeta }(\sigma +it) -\sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{\sigma +it-\rho }\right|\ll \log |t|. \]
Theorem 5.3.24 GapSize
✓

Let \(t\in \mathbb {R}\) with \(|t|\geq 3\) and \(z=\sigma +it\) where \(1-\delta _t/3\leq \sigma \leq 3/2\). Additionally, let \(\rho \in \mathcal{Z}_t\). Then we have that

\[ |z-\rho |\geq \delta _t/6. \]
Proof ▶

Let \(\rho =\sigma '+it'\) and note that since \(\rho \in \mathcal{Z}_t\), we have \(t'\in (t-3/4,t+3/4)\). Thus, if \(t{\gt}1\) we have

\[ \log |t'|\leq \log |t+3/4|\leq \log |2t|=\log 2+\log |t|\leq 2\log |t|. \]

And otherwise if \(t{\lt}-1\) we have

\[ \log |t'|\leq \log |t-3/4|\leq \log |2t|=\log 2+\log |t|\leq 2\log |t|. \]

So by taking reciprocals and multiplying through by a constant we have that \(\delta _t\leq 2\delta _{t'}\). Now note that since \(\rho \in \mathcal{Z}_t\) we know that \(\sigma '\leq 1-\delta _{t'}\) by Theorem 5.3.21 (here we use the fact that \(|t|\geq 3\) to give us that \(|t'|\geq 2\)). Thus,

\[ \delta _t/6\leq \delta _{t'}-\delta _t/3 =1-\delta _t/3-(1-\delta _{t'})\leq \sigma -\sigma '\leq |z-\rho |. \]

There exists a constant \(F\in (0,1/42)\) such that for all \(t\in \mathbb {R}\) with \(|t|\geq 3\) one has

\[ 1-\frac{F}{\log |t|}\leq \sigma \leq 3/2 \implies \left|\frac{\zeta '}{\zeta }(\sigma +it)\right|\ll \log ^2|t| \]

where the implied constant is uniform in \(\sigma \).

Proof ▶

Take \(F=E/3\) where \(E\) comes from Theorem 5.3.21. Then we have that \(\sigma \geq 1-\delta _t/3\). So, we apply Lemma 5.3.23, which gives us that

\[ \left|\frac{\zeta '}{\zeta }(z) -\sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{z-\rho }\right|\ll \log |t|. \]

Using the reverse triangle inequality and rearranging, we have that

\[ \left|\frac{\zeta '}{\zeta }(z)\right| \leq \sum _{\rho \in \mathcal{Z}_t}\frac{m_\zeta (\rho )}{|z-\rho |}+C\, \log |t| \]

where \(C\) is the implied constant in Lemma 5.3.23. Now applying Lemma 5.3.24 we have that

\[ \left|\frac{\zeta '}{\zeta }(z)\right| \leq \frac{6}{\delta _t}\sum _{\rho \in \mathcal{Z}_t}m_\zeta (\rho )+C\, \log |t|. \]

Now let \(f(z)=\zeta (z+3/2+it)/\zeta (3/2+it)\) with \(\rho =\rho '+3/2+it\). Then if \(\rho \in \mathcal{Z}_t\) we have that

\[ 0=\zeta (\rho )=\zeta (\rho '+3/2+it)=f(\rho ') \]

with the same multiplicity of zero, that is \(m_\zeta (\rho )=m_f(\rho ')\). And also if \(\rho \in \mathcal{Z}_t\) then

\[ 3/4\geq |\rho -(3/2+it)|=|\rho '|. \]

Thus we change variables to have that

\[ \left|\frac{\zeta '}{\zeta }(z)\right| \leq \frac{6}{\delta _t}\sum _{\rho '\in \mathcal{K}_f(3/4)}m_f(\rho ')+C\, \log |t|. \]

Now note that \(f(0)=1\) and for \(|z|\leq 5/6\) we have

\[ |f(z)|=\frac{|\zeta (z+3/2+it)|}{|\zeta (3/2+it)|} \leq \frac{\zeta (3/2)}{\zeta (3)}\cdot (7+2\, |t|)\leq \frac{13\, \zeta (3/2)}{3\, \zeta (3)}\, |t| \]

by Theorems 5.3.8 and 5.3.11. Thus by Theorem 5.3.5 we have that

\[ \sum _{\rho '\in \mathcal{K}_f(3/4)}m_f(\rho ') \leq \frac{\log |t|+\log (13\, \zeta (3/2)/(3\, \zeta (3)))}{\log ((5/6)/(3/4))}\leq D\log |t| \]

where \(D\) is taken to be sufficiently large. Recall, by definition that, \(\delta _t=E/\log |t|\) with \(E\) coming from Theorem 5.3.21. By using this fact and the above, we have that

\[ \left|\frac{\zeta '}{\zeta }(z)\right|\ll \log ^2|t|+\log |t| \]

where the implied constant is taken to be bigger than \(6D/E+C\). We know that the RHS is bounded above by \(\ll \log ^2|t|\); so the result follows.

Theorem 5.3.26 LogDerivZetaBdd-of-Re-ge-three-halves
✓
#

There exists a uniform constant \(C\) such that for \(z=\sigma +it\) one has

\[ 3/2\leq \sigma \implies \left|\frac{\zeta '}{\zeta }(z)\right|\leq C. \]
Proof ▶

Note that

\[ \left|\frac{\zeta '}{\zeta }(z)\right|=\left|\sum _{n=1}^\infty \frac{\Lambda (n)}{n^z}\right|\leq \sum _{n=1}^\infty \frac{\Lambda (n)}{|n^z|}=\sum _{n=1}^\infty \frac{\Lambda (n)}{n^\sigma }\leq \sum _{n=1}^\infty \frac{\Lambda (n)}{n^{3/2}}{\lt}\infty \]

by 5.3.19.

Theorem 5.3.27 LogDerivZetaUniformLogSquaredBound
✓

There exists a constant \(F\in (0,1/42)\) such that for all \(t\in \mathbb {R}\) with \(|t|\geq 3\) one has

\[ 1-\frac{F}{\log |t|}\leq \sigma \implies \left|\frac{\zeta '}{\zeta }(\sigma +it)\right|\ll \log ^2|t| \]

where the implied constant is uniform in \(\sigma \).

Proof ▶

Put the previous two Lemmas together.

We have

\[ \sum _{n \leq x}\Lambda (n)=x+O(x \exp (-c(\log x)^{1/2})). \]
Proof ▶

This follows as a corollary of Theorems 4.6.1 and 5.3.27.