Contents
Context
Theta functions
Arithmetic geometry
number theory
number
- natural number, integer number, rational number, real number, irrational number, complex number, quaternion, octonion, adic number, cardinal number, ordinal number, surreal number
arithmetic
arithmetic geometry, function field analogy
Arakelov geometry
Contents
Idea
The Riemann zeta function is the archetypical example of a zeta function, defined by the formula
From the point of view of arithmetic geometry and the function field analogy, the Riemann zeta function is the basic case “over F1” of a tower of zeta functions for arithmetic curves given by more general number fields – the Dedekind zeta functions – and over function fields – the Weil zeta function – and for complex curves – the Selberg zeta function of a Riemann surface – and in another direction for higher dimensional arithmetic schemes – the arithmetic zeta functions.
Properties
Special values
Some of special values of the Riemann zeta function found (for the non-trivial region of non-positive integers) by Leonhard Euler in 1734 and 1749 are
n | -5 | -3 | -1 | 0 | 2 | 4 | 6 | 8 |
---|
| | | | | | | | |
where for instance the value turns out to be the Euler characteristic of the moduli stack of complex elliptic curves and as such controls much of string theory.
The completed zeta function
The following slight variant of the actual Riemann zeta function typically exhibits its special properties more explicitly.
Definition
The completed Riemann zeta function is
where denotes the Gamma function.
Proposition
The completed Riemann zeta function, def. , is the adelic integral
where
-
denotes the function which sends an idele with canonical components
to the product
where denotes the characteristic function of the p-adic integers inside the ring of adeles;
(Goldfeld-Hundley 11, def. 2.2.5).
-
the measure is essentially the Haar measure on the idele group
(Goldfeld-Hundley 11, def. 2.2.3)
(reviewed e.g. in Fesenko 08 0.1, Garrett 11, section 1, Goldfeld-Hundley 11 (2.2.6)).
Relation to the Jacobi theta function
Proposition
The completed zeta function, def. , is the Mellin transform of the Jacobi theta function
in that
e.g. (Fesenko 08, section 0.1, Kowalski, example 2.2.5)
In terms of idelic integral expression for the complete zeta-function of prop. , this comes out as follows:
We compute the integral – as in (Goldfeld-Hundley 11, pages 47-50) and the remarks by Ivan Fesenko in (Goldfeld-Hundley 11, pages 51-51).
We decompose by the strong approximation theorem for ideles the integration domain into the idele class group
and a factor of the non-zero rational numbers: so we write
where runs through representatives of and can be chosen as ideles with non-archimedean coordinates being units in and a positive real number, and is a non-zero rational number.
This way the inner integration is . Due to the definition of in prop. , the integrand here is supported on elements for all , and since we deduce for all . Since intersected with all is (by the arithmetic fracture square), we have
Therefore the full integral becomes with .
Functional equation
The adelic integral representation of prop. directly implies the functional equation
of the completed zeta function from the functional equation of the theta function
which in turn follows from the Poisson summation formula (see at Jacobi theta function – Functional equation).
In terms of the adelic integral expression, the functional equation of the theta function (and of the zeta integral) corresponds to the analytic duality furnished by Fourier transform on the adelic spaces and its subspaces. (due to Tate 50, reviewed for instance in Fesenko 08 0.1, Garrett 11, section 1.9, Goldfeld-Hundley 11 theorem 2.2.12)
This adelic integral-method generalizes to Dedekind zeta functions for any algebraic number field. This is due to (Tate 50), highlighted in (Goldfeld-Hundley 11, Remark (1) by Ivan Fesenko).
…Euler product…
Analogs over number fields, function fields and complex curves
The function field analogy in view of the discussion at zeta function of an elliptic differential operator says that the Riemann zeta function is analogous to the regulated functional trace of a would-be “Dirac operator on Spec(Z)”.
context/function field analogy | theta function | zeta function (= Mellin transform of ) | L-function (= Mellin transform of ) | eta function | special values of L-functions |
---|
physics/2d CFT | partition function as function of complex structure of worldsheet (hence polarization of phase space) and background gauge field/source | analytically continued trace of Feynman propagator | analytically continued trace of Feynman propagator in background gauge field : | analytically continued trace of Dirac propagator in background gauge field | regularized 1-loop vacuum amplitude / regularized fermionic 1-loop vacuum amplitude / vacuum energy |
Riemannian geometry (analysis) | | zeta function of an elliptic differential operator | zeta function of an elliptic differential operator | eta function of a self-adjoint operator | functional determinant, analytic torsion |
complex analytic geometry | section of line bundle over Jacobian variety in terms of covering coordinates on | zeta function of a Riemann surface | Selberg zeta function | | Dedekind eta function |
arithmetic geometry for a function field | | Goss zeta function (for arithmetic curves) and Weil zeta function (in higher dimensional arithmetic geometry) | | | |
arithmetic geometry for a number field | Hecke theta function, automorphic form | Dedekind zeta function (being the Artin L-function for the trivial Galois representation) | Artin L-function of a Galois representation , expressible “in coordinates” (by Artin reciprocity) as a finite-order Hecke L-function (for 1-dimensional representations) and generally (via Langlands correspondence) by an automorphic L-function (for higher dimensional reps) | | class number regulator |
arithmetic geometry for | Jacobi theta function ()/ Dirichlet theta function ( a Dirichlet character) | Riemann zeta function (being the Dirichlet L-function for Dirichlet character ) | Artin L-function of a Galois representation , expressible “in coordinates” (via Artin reciprocity) as a Dirichlet L-function (for 1-dimensional Galois representations) and generally (via Langlands correspondence) as an automorphic L-function | | |
Other identifications/analogies of the Riemann zeta function (and more generally the Dedekind zeta-function) with partition functions in physics have been proposed, in particular the Bost-Connes system.
See also at function field analogy.
References
Discussion in the context of adelic integration and higher arithmetic geometry is in
-
John Tate, Fourier analysis in number fields, and Hecke’s zeta-functions, Algebraic Number Theory (Proc. Instructional Conf., Brighton, 1965), Thompson, Washington, D.C., pp. 305–34 1950
-
Ivan Fesenko, Adelic approch to the zeta function of arithmetic schemes in dimension two, Moscow Math. J. 8 (2008), 273–317 (pdf)
with review including
-
Paul Garrett, Iwasawa-Tate on ζ-functions and L-functions, 2011 (pdf
-
E. Kowalski, first part of Automorphic forms, L-functions and number theory (March 12–16) Three Introductory lectures (pdf)
-
Dorian Goldfeld, Joseph Hundley, chapter 2 of Automorphic representations and L-functions for the general linear group, Cambridge Studies in Advanced Mathematics 129, 2011 (pdf)
Discussion in the context of p-adic string theory: