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I known that there are classical ways to construct $p$-adic $L$ functions for Dirichlet characters through $p$-adic integrals.

We fix a character $\chi$ modulo $Np^r$ with $N$ and $p$ coprime and an integer $b$ coprime with $p$. It is possibile to create a mesure on $(\mathbb{Z}/N\mathbb{Z})^{\times}\times \mathbb{Z}_p^{\times}$ such that the integral of $z_p^k \xi(z)$ (for $z_p$ in $\mathbb{Z}_p^{\times}$, $k\geq 0$ and $\xi$ a character of $(\mathbb{Z}/N\mathbb{Z})^{\times}\times \mathbb{Z}_p^{\times}$ of finite order) is $(1-\xi\chi_1(b)b^{k+1})L_N(-k,\xi\chi)$, where we remove the Euler factors in $N$ and $p$ from the $L$ function of the corresponding primitive character, and $\xi\chi_1$ is the restriction of the character to its $p$-part.

Is there a way to construct similar mesures which would gave $L_N(k,\xi\chi)$? If we define a mesure on $1 + p\mathbb{Z}$ by pullback of the previous mesure, we can then get a mesure which gaves $L_N(-k,\xi\chi\omega^{-k})$ for $\omega$ the Teichm├╝ller character of $\mathbb{Z}_p$. Assuming that the character $\xi\chi\omega^{-k}$ has conductor divisible by $p$, we can easily interpolate the missing Euler factors by the $p$-adic exponential, and then by the complex functional equation it is possible to have, up to trascendental factors and a power of the conductor, $L_N(k+1,\overline{\xi\chi\omega^{-k}})$.

What can we say if the character $\xi\chi\omega^{-k}$ has conductor not divisible by $p$? And is it possible to get some algebraic part of $L_N(k,\xi\chi\omega^{-k})$ integrating $z_p^k \xi(z)$?

Because $z_p^k \xi(z)$ is the function I have to integrate, and $L_N(k,\xi\chi\omega^{-k})$ is the result I need.

I thought about composing this mesure with the inversion of $(\mathbb{Z}/N\mathbb{Z})^{\times}\times \mathbb{Z}_p^{\times}$, but then I should integrate $z_p^{-k}$ and I do not know what I get from it. Maybe it is well-known, but I could not find any references about these kind of integrals at negative powers.

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Generally the values of L-functions at positive integers are transcendental numbers, or are numbers believed to be transcendental. There isn't a natural way to embed these iside an algebraic closure of $\mathbb{}_p$, so I cannot see how there's a sensible notion of interpolation. – Robin Chapman Nov 22 '10 at 16:40
I see your point, but if you multiply the $L$ function associated to the primitive character $L(k,\chi)$ by $i^a \pi^{1/2-k}\frac{\Gamma(\frac{k+a}{2})}{\Gamma(\frac{1-k+a}{2})}$, where $a$ is the parity of your character, then by the complex functional equation you know that it is algebraic. That is the number I would like to interpolate. Those are the numbers I would like to interpolate. Maybe the existence of a functional equation for the $p$-adic $L$ function could help – gvnros Nov 22 '10 at 18:34
If you do that, then basically you have the values at the negative integers. – Robin Chapman Nov 22 '10 at 18:55
ok, thank you very much – gvnros Nov 23 '10 at 13:17

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