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Hyperbolicity of Jensen polynomials
The Jensen-Pólya Program for the Riemann Hypothesis and Related
Problems
Ken Ono (U of Virginia)
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Riemann’s zeta-function
Definition (Riemann)
For Re(s) > 1, define the zeta-function by
ζ(s) :=
∞∑ n=1
1
ns .
Theorem (Fundamental Theorem) 1 The function ζ(s) has an analytic continuation to C (apart
from a simple pole at s = 1 with residue 1).
2 We have the functional equation
ζ(s) = 2sπs−1 sin (πs
2
) Γ(1− s) · ζ(1− s).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Riemann’s zeta-function
Definition (Riemann)
For Re(s) > 1, define the zeta-function by
ζ(s) :=
∞∑ n=1
1
ns .
Theorem (Fundamental Theorem) 1 The function ζ(s) has an analytic continuation to C (apart
from a simple pole at s = 1 with residue 1).
2 We have the functional equation
ζ(s) = 2sπs−1 sin (πs
2
) Γ(1− s) · ζ(1− s).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Riemann’s zeta-function
Definition (Riemann)
For Re(s) > 1, define the zeta-function by
ζ(s) :=
∞∑ n=1
1
ns .
Theorem (Fundamental Theorem) 1 The function ζ(s) has an analytic continuation to C (apart
from a simple pole at s = 1 with residue 1).
2 We have the functional equation
ζ(s) = 2sπs−1 sin (πs
2
) Γ(1− s) · ζ(1− s).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Hilbert’s 8th Problem
Conjecture (Riemann Hypothesis)
Apart from negative evens, the zeros of ζ(s) satisfy Re(s) = 12 .
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Hilbert’s 8th Problem
Conjecture (Riemann Hypothesis)
Apart from negative evens, the zeros of ζ(s) satisfy Re(s) = 12 .
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Important Remarks
Fact (Riemann’s Motivation)
Proposed RH because of Gauss’ Conjecture that π(X) ∼ XlogX .
What is known? 1 The first “gazillion” zeros satisfy RH (van de Lune, Odlyzko).
2 > 41% of zeros satisfy RH (Selberg, Levinson, Conrey,... ).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Important Remarks
Fact (Riemann’s Motivation)
Proposed RH because of Gauss’ Conjecture that π(X) ∼ XlogX .
What is known? 1 The first “gazillion” zeros satisfy RH (van de Lune, Odlyzko).
2 > 41% of zeros satisfy RH (Selberg, Levinson, Conrey,... ).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Important Remarks
Fact (Riemann’s Motivation)
Proposed RH because of Gauss’ Conjecture that π(X) ∼ XlogX .
What is known? 1 The first “gazillion” zeros satisfy RH (van de Lune, Odlyzko).
2 > 41% of zeros satisfy RH (Selberg, Levinson, Conrey,... ).
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen-Pólya Program
J. W. L. Jensen George Pólya (1859−1925) (1887−1985)
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen-Pólya Program
Definition The Riemann Xi-function is the entire function
Ξ(z) := 1
2
( −z2 − 1
4
) π iz 2 − 1
4 Γ
( − iz
2 +
1
4
) ζ
( −iz + 1
2
) .
Remark RH is true ⇐⇒ all of the zeros of Ξ(z) are purely real.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen-Pólya Program
Definition The Riemann Xi-function is the entire function
Ξ(z) := 1
2
( −z2 − 1
4
) π iz 2 − 1
4 Γ
( − iz
2 +
1
4
) ζ
( −iz + 1
2
) .
Remark RH is true ⇐⇒ all of the zeros of Ξ(z) are purely real.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Roots of Deg 100 Taylor Poly for Ξ (
1 2 + z
)
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Roots of Deg 200 Taylor Poly for Ξ (
1 2 + z
)
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Roots of Deg 400 Taylor Poly for Ξ (
1 2 + z
)
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Takeaway about Taylor Polynomials
Red points are good approximations of zeros of Ξ ( 1 2 + z
) .
The “spurious” blue points are annoying.
As d→ +∞ the spurious points become more prevalent.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Takeaway about Taylor Polynomials
Red points are good approximations of zeros of Ξ ( 1 2 + z
) .
The “spurious” blue points are annoying.
As d→ +∞ the spurious points become more prevalent.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Takeaway about Taylor Polynomials
Red points are good approximations of zeros of Ξ ( 1 2 + z
) .
The “spurious” blue points are annoying.
As d→ +∞ the spurious points become more prevalent.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen Polynomials
Definition (Jensen)
The degree d and shift n Jensen polynomial for an arithmetic function a : N 7→ R is
Jd,na (X) :=
d∑ j=0
a(n+ j)
( d j
) Xj
= a(n+ d)Xd + a(n+ d− 1)dXd−1 + · · ·+ a(n).
Definition A polynomial f ∈ R[X] is hyperbolic if all of its roots are real.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen Polynomials
Definition (Jensen)
The degree d and shift n Jensen polynomial for an arithmetic function a : N 7→ R is
Jd,na (X) :=
d∑ j=0
a(n+ j)
( d j
) Xj
= a(n+ d)Xd + a(n+ d− 1)dXd−1 + · · ·+ a(n).
Definition A polynomial f ∈ R[X] is hyperbolic if all of its roots are real.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen’s Criterion
Theorem (Jensen-Pólya (1927))
If Λ(s) := π−s/2Γ(s/2)ζ(s) = Λ(1− s),
then define γ(n) by
( −1 + 4z2
) Λ
( 1
2 + z
) = ∞∑ n=0
γ(n)
n! · z2n.
RH is equivalent to the hyperbolicity of all of the Jd,nγ (X).
What was known? The hyperbolicity for all n is known for d ≤ 3 by work of Csordas, Norfolk and Varga, and Dimitrov and Lucas.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen’s Criterion
Theorem (Jensen-Pólya (1927))
If Λ(s) := π−s/2Γ(s/2)ζ(s) = Λ(1− s), then define γ(n) by
( −1 + 4z2
) Λ
( 1
2 + z
) =
∞∑ n=0
γ(n)
n! · z2n.
RH is equivalent to the hyperbolicity of all of the Jd,nγ (X).
What was known? The hyperbolicity for all n is known for d ≤ 3 by work of Csordas, Norfolk and Varga, and Dimitrov and Lucas.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen’s Criterion
Theorem (Jensen-Pólya (1927))
If Λ(s) := π−s/2Γ(s/2)ζ(s) = Λ(1− s), then define γ(n) by
( −1 + 4z2
) Λ
( 1
2 + z
) =
∞∑ n=0
γ(n)
n! · z2n.
RH is equivalent to the hyperbolicity of all of the Jd,nγ (X).
What was known? The hyperbolicity for all n is known for d ≤ 3 by work of Csordas, Norfolk and Varga, and Dimitrov and Lucas.
Ken Ono (U of Virginia) Hyperbolicity of Jensen polynomials
Hyperbolicity of Jensen polynomials Introduction
Jensen’s Crit
