Twisted Siegel-Weil formulas for ${\mathrm{GL}}_2$ over non-Galois quartic CM fields

Abstract

We establish twisted Siegel-Weil formulas for non-Galois quartic CM fields, identifying the twisted theta integral against a quadratic character with the Doi-Naganuma lift of Hecke's integral. This implies the base change of Jacquet-Langlands correspondence for certain Hecke characters from $\mathbb{Q}$ to real quadratic fields via Doi-Naganuma lift is an isomorphism. As an application, we prove that the twisted CM values of Borcherds forms are algebraic multiple of logarithm of units, explicitly described by the Fourier coefficients of twisted theta integrals.