Generalized elastica problems under area constraint
  It was recently proved that the elastic energy $E(\gamma)=\tfrac{1}{2}\int_\gamma\kappa^2 ds$ of a closed curve $\gamma$ with curvature $\kappa$ has a minimizer among all plane, simple, regular and closed curves of given enclosed area $A(\gamma)$, and that the minimum is attained only for circles. Here we show under which hypothesis the result can be extended to other functionals involving the curvature. As an example we show that the optimal shape remains a circle for the $p$-elastic energy $\int_\gamma|\kappa|^p ds$, whenever $p>1$. 
Vincenzo Ferone, Bernd Kawohl, Carlo Nitsch
math.OC math.AP