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Dirichlet L-series




:L(s,\chi) = \sum_{n=1}^\infty rac{\chi(n)}{n^s}.

Here χ is a Dirichlet Character and ''s'' a complex variable with Real Part greater than 1. By Analytic Continuation , this function can be extended to a Meromorphic Function on the whole Complex Plane , and is then called a Dirichlet ''L''-function and also denoted ''L''(''s'',χ).

It was proven by Dirichlet that ''L''(1,χ)≠0 for all Dirichlet characters χ, allowing him to establish his Theorem On Primes In Arithmetic Progressions . Moreover, if χ is principal, then the corresponding Dirichlet ''L''-function has a simple pole at ''s''=1.


ZEROS OF THE DIRICHLET L-FUNCTIONS


If χ is a primitive character with χ(-1)=1, then the only zeros of ''L''(''s'',χ) with Re(''s'')<0 are at the negative even integers.
If χ is a primitive character with χ(-1)=-1, then the only zeros of ''L''(''s'',χ) with Re(''s'')<0 are at the negative odd integers.

Up to the possible existence of a Siegel Zero , zero-free regions including and beyond the line Re(''s'')=1 similar to that of the Riemann zeta function are known to exist for all Dirichlet ''L''-functions.

Just as the Riemann zeta function is conjectured to obey the Riemann Hypothesis , so the Dirichlet ''L''-functions are conjectured to obey the Generalized Riemann Hypothesis .


FUNCTIONAL EQUATION


Let us assume that χ is a primitive character to the modulus ''k''. Defining

: arepsilon(s,\chi) = \left( rac{\pi}{k} ight)^{-(s+a)/2}
\Gamma\left( rac{s+a}{2} ight) L(s,\chi),

where Γ denotes the Gamma Function and the symbol ''a'' is given by

:a=\begin{cases}0;&\mbox{if }\chi(-1)=1, \ 1;&\mbox{if }\chi(-1)=-1,\end{cases}

one has the Functional Equation

: arepsilon(1-s,\overline{\chi})= rac{i^ak^{1/2}}{ au(\chi)} arepsilon(s,\chi).

Here we wrote τ(χ) for the Gauss Sum

:\sum_{n=1}^k\chi(n)\exp(2\pi in/q).

  {{cite Bookauthor H Davenport