Low energy states of a semiflexible polymer chain with attraction and   the whip-toroid transitions
  Based on our previous paper [cond-mat/0507477], we establish a general model for the whip-toroid transitions of a semiflexible homopolymer chain using the path integral method and the O(3) nonlinear sigma model on a line segment with the local inextensibility constraint. We exactly solve the energy levels of classical solutions, and show that some of its classical configurations exhibit toroidal forms, and the system has phase transitions from a whip to toroidal states with a conformation parameter $c=\frac{W}{2 l} (\frac{L}{2\pi})^2$. We also discuss the stability of the toroid states and propose the low-energy effective Green function. Finally, with the finite size effect on the toroid states, predicted toroidal properties are successfully compared to experimental results of DNA condensation. 
Yukitaka Ishimoto (RIKEN), Norio Kikuchi (U. Mainz)