The finite-subspace reality conjecture for trigonal sigma-functions

Let V\mathcal{V} be a trigonal curve whose finite branch points are real or occur in complex-conjugate pairs. Let i,j\wp_{i,j} and i,j,k\wp_{i,j,k} denote the associated Kleinian functions, let u[ε]u[\varepsilon] be the half-period determined by a half-integer characteristic [ε][\varepsilon], and let gg be the genus. The finite-subspace reality conjecture. There exist 2g2^g affine subspaces

JRe={Ω+ssRg},\mathfrak{J}^{\operatorname{Re}}=\{\Omega+s\mid s\in\mathbb{R}^g\},

parallel to the real axes, with Ω=u[ε]\Omega=u[\varepsilon], such that i,j(s+Ω)\wp_{i,j}(s+\Omega) and i,j,k(s+Ω)\wp_{i,j,k}(s+\Omega) are real-valued and have poles. With the choice of periods specified by the rhombic period-lattice conjecture, the corresponding 2g2^g half-periods are purely imaginary, ΩıRg\Omega\in\imath\mathbb{R}^g. On

JIm={ıssRg},\mathfrak{J}^{\operatorname{Im}}=\{\imath s\mid s\in\mathbb{R}^g\},

the functions i,j(ıs)\wp_{i,j}(\imath s) are real-valued, while i,j,k(ıs)\wp_{i,j,k}(\imath s) are purely imaginary. These reality assertions describe the real and imaginary finite-gap subspaces on which the Kleinian functions provide real-valued data; their resolution is not specified in the source.

Sources & referencesView supporting material

Primary source

Julia Bernatska and Taras Skrypnyk, “Algebro-geometric integration of the Boussinesq hierarchy”, arXiv:2507.19179 (2025).

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