The $D^6 R^4$ interaction as a Poincaré series, and a related shifted convolution sum
Kim Klinger-Logan, Stephen D. Miller, Danylo Radchenko
TL;DR
This work completes the direct construction of the automorphic solution to the inhomogeneous equation $(\Delta-12) f = -\left(2\zeta(3) E_{3/2}\right)^2$ for $SL(2,\mathbb{Z})$ via a Poincaré-series framework, building on the program initiated in GMV2015. It explicitly evaluates the central double integral $\mathcal{I}(n_1,n_2;y)$ in the Fourier expansion for the critical case $a=\tfrac{3}{2}$, $\lambda=12$, and shows the resulting Fourier modes align with the previously known structure, including the homogeneous part. A formal double-Dirichlet-series analysis yields the predicted vanishing of the total homogeneous coefficient sum over nonzero modes, matching physics-inspired conjectures (and later proven rigorously in follow-up work). The methods extend to both half-integer and integer $a$, offering a concrete route to solving similar automorphic differential equations arising in string theory and related automorphic-form contexts.
Abstract
We complete the program, initiated in a 2015 paper of Green, Miller, and Vanhove, of directly constructing the automorphic solution to the string theory $D^6 R^4$ differential equation $(Δ-12)f=-E_{3/2}^2$ for $SL(2,\Z)$. The construction is via a type of Poincaré series, and requires explicitly evaluating a particular double integral. We also show how to use double Dirichlet series to formally derive the predicted vanishing of one type of term appearing in $f$'s Fourier expansion, confirming a conjecture made by Chester, Green, Pufu, Wang, and Wen motivated by Yang-Mills theory (and later proved rigorously by Fedosova, Klinger-Logan, and Radchenko using the Gross-Zagier Holomorphic Projection Lemma.).
