A critical point analysis of Landau--Ginzburg potentials with bulk in Gelfand--Cetlin systems

Using the bulk-deformation of Floer cohomology by Schubert cycles and non-Archimedean analysis of Fukaya–Oh–Ohta–Ono’s bulk-deformed potential function, we prove that every complete flag manifold $\mathrm{F}\mathrm{l}(n)$ ($n \geq 3$) with a monotone Kirillov–Kostant–Souriau symplectic form carries a continuum of non-displaceable Lagrangian tori which degenerates to a non-torus fiber in the Hausdorff limit. In particular, the Lagrangian $S^3$-fiber in $\mathrm{F}\mathrm{l}(3)$ is non-displaceable, answering the question of which was raised by Nohara–Ueda who computed its Floer cohomology to be vanishing.