The representation-number doubling conjecture for maximal lattices

Let V\mathcal V be a totally positive definite quadratic space over a totally real number field kk of dimension gg. Fix a maximal integral lattice LL of V\mathcal V, and let T12Eg(o)T\in\frac{1}{2}\mathcal E_g(\mathfrak o) be totally positive definite. Write R(L,T)R(L,T) for the representation number of TT by LL. If gg is even and χV=1\chi^{\mathcal V}=1, then there is a totally positive definite matrix T12Eg1(o)T'\in\frac{1}{2}\mathcal E_{g-1}(\mathfrak o) such that

R(L,T)=2R(L,T).R(L,T)=2R(L,T').

Representation-number doubling conjecture. Under these hypotheses, such a matrix TT' exists and the representation number satisfies the displayed doubling identity. The claim concerns a relation between representation numbers of a maximal lattice and totally positive definite matrices of consecutive sizes; the supplied text does not indicate whether it has been proved or remains open.

Sources & referencesView supporting material

Primary source

Sungmun Cho, Shunsuke Yamana and Takuya Yamauchi, “Derivatives of Eisenstein series of weight 2 and intersections of modular correspondences”, arXiv:1802.06273 (2018).

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