On central configurations of twisted crowns
  We consider the planar central configurations of the Newtonian $\kappa n$-body problem consisting in $\kappa$ groups of $n$-gons where all $n$ bodies in each group have the same mass, called $(\kappa, n)$-crown. We study the location and the number of central configurations when $\kappa=2$. For $n=3$ the number of central configurations varies depending on the mass ratio, whereas for $n\geq 4$ the number is at least three. We also prove that for $n\geq 3$ there always exist three disjoint regions where the configuration can be located. Finally, we study which $(\kappa, n)$-crowns are convex. 
E. Barrab\'es and J.M. Cors
math.DS