A Non-Split Motohashi Formula for Toric Periods over Number Fields

Source abstract

We establish a non-split Motohashi formula for toric Eisenstein periods over an arbitrary number field $F$. For a quadratic extension $E/F$, we compare toric Fourier inversion for a product of two Eisenstein series with the $\mathrm{GL}_2/F$-spectral expansion of its Rankin--Selberg kernel. The kernel regularizes the product in a cone of absolute convergence. Eisenstein corrections and contour residues give the geometric and residual terms in the meromorphically continued identity. Suitable test data give twisted first- and second-moment formulas for the completed $L$-functions of everywhere unramified toric characters. Over general $F$ these provide an adelic counterpart of the moment formulas of Duke--Friedlander--Iwaniec that does not use the geometry of Heegner points. In the CM case, we prove the absolute nonvanishing proportion $4.9\times10^{-4}$ for every totally real base field and all sufficiently large CM discriminants, with the threshold depending on the base field and no restriction on the number of ramified primes. We incorporate inverse Euler factors at small ramified primes into the mollifier. Local unit-group tests control the resulting moments and remove the ramified Euler-factor loss.