Zagier's 2-3-2 formula for multiple Eisenstein series

Abstract: We prove a multiple Eisenstein series analogue of Zagier's formula for the multiple zeta values $ζ(2,\ldots,2,3,2,\ldots,2)$. The multiple Eisenstein series identity contains correction terms given by derivatives of odd Eisenstein series. Using the Goncharov coproduct and Brown's motivic version of Zagier's formula, we show that the normalized difference has rational Fourier coefficients. We then use the $\mathfrak{sl}_2$-structure and a modularity criterion of Yu to prove the identity by induction.