A theory of generalized Lam\'e curves

Abstract

We study the generalized Lam\'e equation on an elliptic curve $E$ with multiple singularities. By restricting to the locus admitting solutions with quasi-periodic properties, we construct two curves: (i) The generalized Lam'e curve: with $n:=\sum\nolimits_{i=1}^r n_i\in\mathbb Z_{\geq 0}$, we construct $\mathcal{Y}_{\mathbf n}(\mathbf p;\tau)$, which lies in an affine bundle over $Sym^n E$ and parametrizes generalized Hermite--Halphen ansatz solutions. (ii) The log-free curve: each $n_i\in\frac12\mathbb N$ gives a polynomial equation in the accessory parameters. This leads to a non-complete intersection variety $V_{\mathbf{n}}(\mathbf{p};\tau)$ when all $n_i\in\frac12\mathbb N$. We prove that it is a reduced curve. We analysis the GLC as an algebraic family over the pole configuration space $\mathbf{p}$. We study the shifted addition map \[ \sigma: Sym^n E\longrightarrow E, \] establishing a generically finite, degree formula. The geometry of boundary degenerations under pole collisions perfectly mirrors the tensor algebra of $\mathfrak{sl}_2(\mathbb{C})$-modules within the BGG category $\mathcal{O}$. We generalize pre-modular forms to a framework of twisted isomonodromic deformations. We construct $(\mathbf{n}, \mathbf{p})$-deformed pre-modular forms parameterized by pseudo-monodromy data $(t,s)$, whose vanishing governs these deformations and factorizes along boundary strata. Iterating these deformations through the boundary allows any arbitrary configuration to be continuously deformed down to the classical Lam\'e equation. Finally, we prove the Treibich conjecture stated for $r=2$ extra symmetric pairs, as well as its generalizations for $r \leq 4$.