Relative Equilibria in the Four-Vortex Problem with Two Pairs of Equal Vorticities

Abstract

We examine in detail the relative equilibria in the four-vortex problem where two pairs of vortices have equal strength, that is, Γ_1 = Γ_2 = 1 and Γ_3 = Γ_4 = m where m is a nonzero real parameter. One main result is that for m > 0, the convex configurations all contain a line of symmetry, forming a rhombus or an isosceles trapezoid. The rhombus solutions exist for all m but the isosceles trapezoid case exists only when m is positive. In fact, there exist asymmetric convex configurations when m < 0. In contrast to the Newtonian four-body problem with two equal pairs of masses, where the symmetry of all convex central configurations is unproven, the equations in the vortex case are easier to handle, allowing for a complete classification of all solutions. Precise counts on the number and type of solutions (equivalence classes) for different values of m, as well as a description of some of the bifurcations that occur, are provided. Our techniques involve a combination of analysis and modern and computational algebraic geometry.

References in corpus (2)

• Some Problems on the Classical N-Body Problem
• Convex Four Body Central Configurations with Some Equal Masses

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• Planarity conditions and four-body central configurations equations with angles as coordinates
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• Nonlinear Stability of Relative Equilibria in the Planar $N$-Vortex Problem with Non-Zero Total Circulation