Complex structures adapted to magnetic flows

Abstract

Let $M$ be a compact real-analytic manifold, equipped with a real-analytic Riemannian metric $g,$ and let $\beta$ be a closed real-analytic 2-form on $M$, interpreted as a magnetic field. Consider the Hamiltonian flow on $T^*M$ that describes a charged particle moving in the magnetic field $\beta$. Following an idea of T. Thiemann, we construct a complex structure on a tube inside $T^*M$ by pushing forward the vertical polarization by the Hamiltonian flow "evaluated at time $i$." This complex structure fits together with $\omega-\pi^*\beta$ to give a Kaehler structure on a tube inside $T^*M$. We describe this magnetic complex structure in terms of its $(1,0)$-tangent bundle, at the level of holomorphic functions, and via a construction using the embeddings of Whitney-Bruhat and Grauert, which is a magnetic analogue to the analytic continuation of the geometric exponential map. We describe an antiholomorphic intertwiner between this complex structure and the complex structure induced by $-\beta$, and we give two formulas for local Kaehler potentials, which depend on a local choice of vector potential 1-form for $\beta$. When $\beta=0$, our magnetic complex structure is the adapted complex structure of Lempert-Sz\H{o}ke and Guillemin-Stenzel. We compute the magnetic complex structure explicitly for constant magnetic fields on $\mathbb{R}^{2}$ and $S^{2}.$ In the $\mathbb{R}^{2}$ case, the magnetic adapted complex structure for a constant magnetic field is related to work of Kr\"otz-Thangavelu-Xu on heat kernel analysis on the Heisenberg group.