The norm relations test for positive rank of elliptic curves

Let EE be an elliptic curve over Q\mathbb{Q}, let F/QF / \mathbb{Q} be a finite Galois extension with G=Gal(F/Q)G = \operatorname{Gal}(F / \mathbb{Q}), and let ρ\rho be an irreducible representation of GG. Write Q(ρ)\mathbb{Q}(\rho) for the field generated by the character values of ρ\rho, and for σGal(Q(ρ)/Q)\sigma \in \operatorname{Gal}(\mathbb{Q}(\rho) / \mathbb{Q}) let ρσ\rho^\sigma denote the Galois-conjugate representation. Suppose that

(σGal(Q(ρ)/Q)ρσ)m=(iC[G/Hi])(jC[G/Hj])\left( \bigoplus_{\sigma \in \operatorname{Gal}(\mathbb{Q}(\rho) / \mathbb{Q})} \rho^\sigma \right)^{\oplus m} = \left( \bigoplus_i \mathbb{C}[G / H_i] \right) \ominus \left( \bigoplus_j \mathbb{C}[G / H_j'] \right)

for some m1m \geq 1 and subgroups Hi,HjGH_i,H_j' \leq G. Norm relations test. If either

iCE/FHijCE/FHj\frac{\prod_i C_{E / F^{H_i}}}{\prod_j C_{E / F^{H_j'}}}

is not a norm from some quadratic field Q(D)Q(ρ)\mathbb{Q}(\sqrt{D}) \subset \mathbb{Q}(\rho), or is not a rational square when mm is even, then EE has a point of infinite order over FF. The test is based on the conjectural properties of the Birch–Swinnerton-Dyer quotient and is known in the source to follow from the parity conjecture for twists under stated hypotheses, while its unconditional conjectural status is not resolved there.

Sources & referencesView supporting material

Primary source

Edwina Aylward, “Tamagawa numbers and positive rank of elliptic curves”, arXiv:2504.17962 (2026).

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