A certain identity for certain Fourier transforms, equating a sum or integral of a function over a domain (e.g., a lattice) with a corresponding sum or integral of its Fourier dual over a dual domain (e.g., the dual lattice).
The Poisson summation formula is basic to harmonic analysis over general locally compact Hausdorff abelian groups.
Consider an exact sequence in of locally compact Hausdorff abelian groups
where are equipped with Haar measures that make the following equation true:
for all continuous functions with compact support. (The inner integral on the right is a shorthand for for any that maps to ; this is well-defined since the integral is invariant under changes within the same coset .) We remark that given Haar measures , there exists a Haar measure making this Fubini-type equation true. Then, since Haar measures form a torsor over the group of positive reals with multiplication, it follows that any two of determine the third.
In this notation, the “Poisson summation formula” is the equation asserted by the following result.
Let denote the Pontryagin dual of , and the dual Haar measure. For any Schwartz-Bruhat function , we have
where is the Fourier transform of , as a function on defined by
In the special case of a lattice inside , the dual space is a lattice inside , and the integrals are over discrete spaces, i.e. integration is just summation and we have
where is the Haar measure on (as above). Often the measure on is chosen so that .
The classical case is when is a Euclidean space . But another case of a lattice inside locally compact abelian groups occurs in the context of Tate’s thesis, where a global field is viewed as a lattice inside its ring of adeles.
A nonabelian version of the Poisson summation formula is the Selberg trace formula.
Reviews include
theorem 4.1 in Analytic theory of modular forms pdf
E. Kowalski, prop. 2.2.1 in Automorphic forms, L-functions and number theory (March 12–16) Three Introductory lectures (pdf)
An application to zeta functions via harmonic analysis on adele rings originates in Tate’s thesis:
A textbook account is
and brief review in
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