Pavel Exner
An isoperimetric problem for point interactions
(27K, LaTeX)

ABSTRACT.  We consider Hamiltonian with $N$ point interactions in $\R^d,\:
d=2,3,$ all with the same coupling constant, placed at vertices
of an equilateral polygon $\PP_N$. It is shown that the ground
state energy is locally maximized by a regular polygon. The
question whether the maximum is global is reduced to an
interesting geometric problem.