Nets of standard subspaces on Lie groups

Karl-Hermann Neeb, Gestur Olafsson

Published 2020-06-16Version 1

Let G be a Lie group with Lie algebra $\mathfrak{g}$, $h \in \frak{g}$ an element for which the derivation ad(h) defines a 3-grading of $\mathfrak{g}$ and $\tau_G$ an involutive automorphism of G inducing on $\mathfrak{g}$ the involution $e^{\pi i ad(h)}$. We consider antiunitary representations $U$ of the Lie group $G_\tau = G \rtimes \{e,\tau_G\}$ for which the positive cone $C_U = \{ x \in \mathfrak{g} : -i \partial U(x) \geq 0\}$ and $h$ span $\mathfrak{g}$. To a real subspace E of distribution vectors invariant under $exp(\mathbb{R} h)$ and an open subset $O \subseteq G$, we associate the real subspace $H_E(O) \subseteq H$, generated by the subspaces $U(\varphi)E$, where $\varphi \in C^\infty_c(O,\mathbb{R})$ is a real-valued test function on $O$. Then $H_E(O)$ is dense in $H_E(G)$ for every non-empty open subset $O \subseteq G$ (Reeh--Schlider property). For the real standard subspace $V \subseteq H$, for which $J_V = U(\tau_G)$ is the modular conjugation and $\Delta_V^{-it/2\pi} = U(\exp th)$ is the modular group, we obtain sufficient conditions to be of the form $H_E(S)$ for an open subsemigroup $S \subseteq G$. If $\mathfrak{g}$ is semisimple with simple hermitian ideals of tube type, we verify these criteria and obtain nets of standard subspacs $H_E(O)$, $O \subseteq G$, satisfying the Bisognano--Wichman property. Our construction also yields such nets on simple Jordan space-times and compactly causal symmetric spaces of Cayley type. By second quantization, these nets lead to free quantum fields in the sense of Haag--Kastler on causal homogeneous spaces whose groups are generated by modular groups and conjugations.