Schur theorem for the Ricci curvature of any weakly Landsberg Finsler metric
摘要
The Ricci version of the Schur theorem is shown to hold for a wide class of Finsler metrics. What is more, let F be any Finsler metric whose Ricci curvature is a function ρ: Mn → ℝ (i.e., (Mn, F) is Einstein), where n ≥ 3. For x ∈ M, we express dρx as an average over the indicatrix in TxM of the Hilbert form weighted by a combination of derivatives of the Landsberg tensor. As a consequence of this general expression, if the metric is weakly Landsberg, then ρ must be constant. The proof is based on the invariance of certain functionals under Diff(M).
Furthermore, the Schur theorem holds for the class of pseudo-Finsler metrics with quadratic Ricci scalar. We extend previous arguments in the literature that proved this in particular cases. Lastly, we analyze the status of the general problem.