An introduction to p-adic L-functions — Lean blueprint

6.1. The two formulae at s = 1🔗

Theorem6.1.1
Statement uses 4
Statement dependency previews
Preview
Definition 2.1.3
Loading preview
Statement dependency preview content is loaded from the Blueprint HTML cache.
used by 1XL∃∀N

Let \theta be a non-trivial Dirichlet character of conductor N, and let \varepsilon_N be a primitive N-th root of unity.

(i) Classical value at s=1. We have L(\theta,1) = -\frac{1}{G(\theta^{-1})}\sum_{c\in(\Z/N\Z)^\times}\theta^{-1}(c)\,\log\!\big(1-\varepsilon_N^{\,c}\big).

(ii) p-adic value at s=1. We have L_p(\theta,1) = -\big(1-\theta(p)p^{-1}\big)\frac{1}{G(\theta^{-1})}\sum_{c\in(\Z/N\Z)^\times}\theta^{-1}(c)\,\log_p\!\big(1-\varepsilon_N^{\,c}\big).

Part (i) rests on the special-value description of Definition 2.1.3. Part (ii) concerns the value at s=1 of the Definition 4.3.2 p-adic L-function, which lies outside the range of the Theorem 5.1.1, and is computed from the measures Definition 4.1.4.

The two formulae are identical up to replacing the complex logarithm \log by its p-adic avatar \log_p and inserting the missing Euler factor at p, namely (1-\theta(p)p^{-1}). If \theta is odd, both sides of the p-adic formula vanish.