Uniqueness Theorems for Variational Problems by the Method of Transformation Groups

A classical problem in the calculus of variations is the investigation of critical points of functionals {\cal L} on normed spaces V. The present work addresses the question: Under what conditions on the functional {\cal L} and the underlying space V does {\cal L} have at most one critical point?A sufficient condition for uniqueness is given: the presence of a "e;variational sub-symmetry"e;, i.e., a one-parameter group G of transformations of V, which strictly reduces the values of {\cal L}. The "e;method of transformation groups"e; is applied to second-order elliptic boundary value problems on Riemannian manifolds. Further applications include problems of geometric analysis and elasticity.