Brane Partons and Singleton Strings
  We examine p-branes in AdS(D) in two limits where they exhibit partonic behavior: rotating branes with energy concentrated to cusp-like solitons; tensionless branes with energy distributed over singletonic partons on the Dirac hypercone. Evidence for a smooth transition from cusps to partons is found. First, each cusp yields D-2 normal-coordinate bound states with protected frequencies (for p>2 there are additional bound states); and can moreover be related to a short open p-brane whose tension diverges at the AdS boundary leading to a decoupled singular CFT at the ``brane at the end-of-the-universe''. Second, discretizing the closed p-brane and keeping the number N of discrete partons finite yields an sp(2N)-gauged phase-space sigma model giving rise to symmetrized N-tupletons of the minimal higher-spin algebra ho_0(D-1,2)\supset so(D-1,2). The continuum limit leads to a 2d chiral sp(2)-gauged sigma model which is critical in D=7; equivalent a la Bars-Vasiliev to an su(2)-gauged spinor string; and furthermore dual to a WZW model in turn containing a topological \hat{so}(6,2)_{-2}/(\hat{so}(6)\oplus \hat\so(2))_{-2} coset model with a chiral ring generated by singleton-valued weight-0 spin fields. Moreover, the two-parton truncation can be linked via a reformulation a la Cattaneo-Felder-Kontsevich to a topological open string on the phase space of the D-dimensional Dirac hypercone. We present evidence that a suitable deformation of the open string leads to the Vasiliev equations based on vector oscillators and weak sp(2)-projection. Geometrically, the bi-locality reflects broken boundary-singleton worldlines, while Vasiliev's intertwiner kappa can be seen to relate T and R-ordered deformations of the boundary and the bulk of the worldsheet, respectively. 
J. Engquist and P. Sundell