- Generalized Riemann hypothesis
Riemann hypothesisis one of the most important conjectures in mathematics. It is a statement about the zeros of the Riemann zeta function. Various geometrical and arithmetical objects can be described by so-called global L-functions, which are formally similar to the Riemann zeta-function. One can then ask the same question about the zeros of these "L"-functions, yielding various generalizations of the Riemann hypothesis. Many mathematicians believe these generalizations of the Riemann hypothesis to be true. The only cases of these conjectures which have been proven occur in the function field case (not the number field case).
Global "L"-functions can be associated to
elliptic curves, number fields (in which case they are called Dedekind zeta-functions), Maass forms, and Dirichlet characters (in which case they are called Dirichlet L-functions). When the Riemann hypothesis is formulated for Dedekind zeta-functions, it is known as the extended Riemann hypothesis (ERH) and when it is formulated for Dirichlet "L"-functions, it is known as the generalized Riemann hypothesis (GRH). These two statements will be discussed in more detail below. (Many mathematicians use the label "generalized Riemann hypothesis" to cover the extension of the Riemann hypothesis to all global "L"-functions, not just the special case of Dirichlet "L"-functions.)
Generalized Riemann hypothesis (GRH)
The generalized Riemann hypothesis (for Dirichlet "L"-functions) was probably formulated for the first time by Piltz in 1884. Like the original Riemann hypothesis, it has far reaching consequences about the distribution of
The formal statement of the hypothesis follows. A
Dirichlet characteris a completely multiplicative arithmetic functionχ such that there exists a positive integer "k" with χ("n" + "k") = χ("n") for all "n" and χ("n") = 0 whenever gcd("n", "k") > 1. If such a character is given, we define the corresponding Dirichlet L-function by:
complex number"s" with real part > 1. By analytic continuation, this function can be extended to a meromorphic functiondefined on the whole complex plane. The generalized Riemann hypothesis asserts that for every Dirichlet character χ and every complex number "s" with L(χ,"s") = 0: if the real part of "s" is between 0 and 1, then it is actually 1/2.
The case χ("n") = 1 for all "n" yields the ordinary Riemann hypothesis.
Consequences of GRH
An "arithmetic progression" in the
natural numbers is a set of numbers of the form "a", "a"+"d", "a"+2"d", "a"+3"d", ... where "a" and "d" are natural numbers and "d" is non-zero.
Dirichlet's theorem states that if "a" and "d" are
coprime, then such an arithmetic progression contains infinitely many prime numbers.Let π("x","a","d") denote the number of prime numbers in this progression which are less than or equal to "x".If the generalized Riemann hypothesis is true, then for every coprime "a" and "d" and for every ε > 0
where φ("d") denotes
Euler's phi functionand O is the Landau symbol. This is a considerable strengthening of the prime number theorem.
If GRH is true, then for every prime "p" there exists a primitive root modulo "p" (a generator of the multiplicative group of integers modulo "p") which is less than 70 (ln("p"))2; this is often used in proofs.
Goldbach's weak conjecturealso follows from the generalized Riemann hypothesis.
If GRH is true, then the
Miller-Rabin primality testis guaranteed to run in polynomial time. (A polynomial-time primality test which does not require GRH, the AKS primality test, was published in 2002.)
If GRH is true, then
Shanks-Tonelli algorithmis guaranteed to run in polynomial time. Shanks-Tonelli algorithm isuseful for finding solutions to: where "n" is a quadratic residuemod p,"p" is prime and x is the unknown variable. This algorithm is an important step inthe Quadratic Sieve( Carl Pomerance) factoring algorithm.
Assuming the truth of the GRH, the estimate of the character sum in the
Pólya-Vinogradov inequalitycan be improved to , "q" being the modulus of the character.
Extended Riemann hypothesis (ERH)
Suppose "K" is a
number field(a finite-dimensional field extensionof the rationals Q) with ring of integers O"K" (this ring is the integral closureof the integers Z in "K"). If "a" is an ideal of O"K", other than the zero ideal we denote its norm by "Na". The Dedekind zeta-functionof "K" is then defined by:for every complex number "s" with real part > 1. The sum extends over all non-zero ideals "a" of O"K".
The Dedekind zeta-function satisfies a functional equation and can be extended by
analytic continuationto the whole complex plane. The resulting function encodes important information about the number field "K". The extended Riemann hypothesis asserts that for every number field "K" and every complex number "s" with ζ"K"("s") = 0: if the real part of "s" is between 0 and 1, then it is in fact 1/2.
The ordinary Riemann hypothesis follows from the extended one if one takes the number field to be Q, with ring of integers Z.
* Artin's conjecture
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