Let
k be a real abelian number field with Galois group
Δ and
p an odd prime number. Assume that the order of
Δ is not divisible by
p. Let
Ψ be an irreducible
Qp-character of
Δ. Denote by λ
p(
Ψ ) the
Ψ-component of the λ-invariant associated to the cyclotomic
Zp-extension of
k. Then Greenberg conjecture for the
Ψ-components states that λ
p(
Ψ ) is always zero for any
Ψ and
p. Although some efficient criteria for the conjecture to be true are given, very little is known about it except for
k =
Q or the trivial character case.
There is another λ-invariant. Denote by λ
p*(
Ψ ) the λ-invariant associated to the
p -adic
L-function related to
Ψ. One can know λ
p*(
Ψ ) by computing the Iwasawa power series attached to
Ψ. The Iwasawa main conjecture proved by Mazur and Wiles says that the inequality λ
p(
Ψ ) ≤ λ
p*(
Ψ ) holds. In this paper, we give a necessary and sufficient condition for this inequality to be strict in terms of special values of
p -adic
L-functions. This result enables us to obtain a criterion for Greenberg’s conjecture for
Ψ-components to be true when the corresponding Iwasawa power series is irreducible.
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