On angles in Teichm\"uller spaces

Abstract

We discuss the existence of the angle between two curves in Teichm\"uller spaces and show that, in any infinite dimensional Teichm\"uller space, there exist infinitely many geodesic triangles each of which has the same three vertices and satisfies the property that its three sides have the same and arbitrarily given length while its three angles are equal to any given three possibly different numbers from 0 to $\pi$. This implies that the sum of three angles of a geodesic triangle may be equal to any given number from 0 to $3\pi$ in an infinite dimensional Teichm\"uller space.