Title:On the existence of a balanced vertex in geodesic nets with three boundary vertices

Abstract:Geodesic nets are types of graphs in Riemannian manifolds where each edge is a geodesic segment. One important object used in the construction of geodesic nets is a balanced vertex, where the sum of unit tangent vectors along adjacent edges is zero. In 2021, Parsch proved the upper bound for the number of balanced vertices of a geodesic net with three unbalanced vertices on surfaces with non-positive curvature. We extend his result by proving the existence of a balanced vertex of a triangle (with three unbalanced vertices) on any two-dimensional surface when all angles measure less than $2\pi/3$, if the length of the sides of the triangle are not too large. This property is also a generalization for the existence of the Fermat point of a planar triangle.