Chevyrev–Galbraith's optimal domination conjecture for maximal quaternion orders

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Let pp be a prime and let BpB_p be the quaternion algebra over Q\mathbb{Q} ramified precisely at pp and ∞\infty. Let O\mathcal{O} and O′\mathcal{O}' be maximal orders of BpB_p. For a maximal order O\mathcal{O}, write OT\mathcal{O}^{T} for its associated trace-zero lattice, and let aOT(n)a_{\mathcal{O}^{T}}(n) denote the relevant Fourier coefficient. Say that O′T\mathcal{O}'^{T} optimally dominates OT\mathcal{O}^{T} if

aO′T(n)≥aOT(n)a_{\mathcal{O}'^{T}}(n)\geq a_{\mathcal{O}^{T}}(n)

for every n∈N0n\in\mathbb{N}_0. Chevyrev–Galbraith's conjecture. If O′T\mathcal{O}'^{T} optimally dominates OT\mathcal{O}^{T}, then O\mathcal{O} and O′\mathcal{O}' are of the same type. This means that they are conjugate by a nonzero element of BpB_p. The conjecture is precisely the condition expected to ensure termination of the Chevyrev–Galbraith algorithm for constructing a supersingular elliptic curve with a prescribed maximal endomorphism ring; its resolution is not established in the supplied text.

References

Primary source

King Cheong Fung and Ben Kane, “On sign changes of cusp forms and the halting of an algorithm to construct a supersingular elliptic curve with a given endomorphism ring”, arXiv:1511.02082 (2016).

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