Quantum Hall Skyrmions in the framework of O(4) Non-linear Sigma Model
  A new framework for quantum Hall skyrmions in O(4) nonlinear sigma model is studied here. The size and energy of the skyrmions are determined incorporating the quartic stability term in the Lagrangian. Moreover, the introduction of a $\theta$-term determines the spin and statistics of these skyrmions. 
B. Basu, S. Dhar and P. Bandyopadhyay