We prove the compatibility of arithmetic local constants of Mazur and Rubin with the usual local constants for pairs of congruent self-dual Galois representations that become Barsotti-Tate over a tamely ramified abelian extension. This allows us to complete the proof of the p-parity conjecture (p > 2) for Selmer groups of Hilbert modular forms of parallel weight 2 and abelian varieties with real multiplication (in particular, elliptic curves) over totally real number fields.
IntroductionLet L be a finite extension of Q , let K be a finite extension of Q p (where p > 2) with ring of integers O, and let V be a finite-dimensional vector space over K equipped with a continuous K-linear action of Γ L = Gal(L/L). Assume that V is self-dual in the sense that there exists a Γ L -equivariant nondegenerate skew-symmetric pairing ,is a uniformiser) has coefficients in the finite field F := O/πO and the skew-symmetric pairing , :representation of the Weil-Deligne group of L attached to V (respectively to D pst (V ), [26; 27, I.1.3.2]) if = p (respectively if = p). Let ψ be a nontrivial additive character of L and dx ψ the Haar measure on L that is self-dual with respect to ψ. The local constant ε(V ) := ε(W D(V ), ψ, dx ψ ) does not depend on ψ and is equal to ±1 [37, Proposition 2.2.1]. Mazur and Rubin expect their arithmetic local constant δ L (T, T ) to be related to ε(V )/ε(V ). This was checked by explicit calculations in certain cases arising from abelian varieties [17]. It was subsequently proved [41, Theorem 2.17] thatholds in full generality if = p. One expects this relation to be true even if = p, provided the Hodge-Tate weights of V and V are the same (including the multiplicities). This was verified in two very special cases in [41, § 3].The main local result of the present article is the following.Theorem A (= Theorem 5.5). If = p = 2 and if there exist abelian tamely ramified finite extensions K/L and K /L and p-divisible groups (equipped with an O-action
JAN NEKOVÁŘtogether with the existence of a cohomological version of the Cassels-Tate pairing constructed by Flach [24, Theorem 1] imply that Theorem 2.17] and for v | p in Theorem A imply the following result (the assumption of tame ramification is no longer necessary, since the statement is invariant under base change to an arbitrary abelian extension of odd degree).Theorem B (= Theorem 6.7). Assume that, in the global situation considered above, for every prime v | p of L there exist finite abelian extensionswhere ε(V ) := v ε v (V ) and ε(V ) := v ε v (V ) (the product is taken over all primes of L and ε v (V ) = ε v (V ) := (−1) dimK(V )/2 for all v | ∞).