A Complete Proof of Mueller--Ho Conjecture

Abstract

For $s>0$, and $z\in\mathbb H=\{z=x+iy:y>0\}$, define $θ(s;z)=\sum_{m,n\in\mathbb Z}e^{-πs\big(m^2y+\frac{(mx-n)^2}{y}\big)}$ and $ J(z;a,b)=\sum_{m,n\in\mathbb Z}e^{-π\big(m^2y+\frac{(mx-n)^2}{y}\big)} \cos\bigl(2π(ma+nb)\bigr)$ for the classical and shifted theta functions (Gaussian lattice sums), respectively. We prove that, up to the modular group, there exist three thresholds $0<α_a<α_b<α_c<1$ such that \begin{equation}\aligned\nonumber \Minima_{z\in\mathbb H,\,(a,b)\in\mathbb R^2}\Big(θ(1;z)+αJ(z;a,b)\Big)= \begin{cases} \;\big(e^{iπ/{3}};1/3,1/3\big), &\hbox{if}\;\; α\in[0,α_a),\\ \;\big(e^{iπ/{3}};1/3,1/3\big)\;\hbox{or}\;\big(e^{i{φ_{α_a}}};1/2,1/2\big), &\hbox{if}\;\; α=α_a,\\ \;\big(e^{i{φ_α}};1/2,1/2\big),\;φ_α\in(φ_{α_a},\fracπ{2}),\;\; &\hbox{if}\;\; α\in(α_a,α_b),\\ \;\big(i;1/2,1/2\big),\; &\hbox{if}\;\; α\in[α_b,α_c],\\ \;\big(iy_α;1/2,1/2\big),\; y_α\in(1,\sqrt3],\;\;y_1=\sqrt3,\;\;&\hbox{if}\;\; α\in(α_c,1], \end{cases} \endaligned\end{equation} where the complex variable $z$ and vector $(a,b)$, represent the total vortex shapes and relative positions of the two-component Bose gas, respectively. Consequently, this completely proves the conjecture of Mueller and Ho~\cite{Mue2002} (2002) arising in Bose--Einstein condensates.