The field-of-definition conjecture for the zeros of hχh_\chi

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Let NN be a prime level, let χ\chi be the character used to define hχh_\chi, and let Bm,χB_{m,\chi} denote the mm-th generalised Bernoulli number attached to χ\chi. Write

k=Q(N).k=\mathbb{Q}(\sqrt{N}).

For each zero of hχh_\chi, consider its field of definition. Field-of-definition conjecture. The field of definition of each zero of hχh_\chi is either Q\mathbb{Q} or an extension FF of the real quadratic field kk of degree

n=12B2,χn=\frac{1}{2}B_{2,\chi}

if N≡1(mod8)N\equiv 1\pmod{8}, and of degree

n=12B2,χ−1n=\frac{1}{2}B_{2,\chi}-1

if N≡5(mod8)N\equiv 5\pmod{8}. This conjecture is motivated by computations of the polynomials pN(T)p_N(T) and concerns the arithmetic fields generated by the zeros of hχh_\chi; the supplied text gives no resolution, so its status remains open.

References

Primary source

Carlos Castano-Bernard, “Further properties of a function of Ogg and Ligozat”, arXiv:math/0603016 (2006).

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