Poincare Invariance in Multiple D-brane Actions
  We show that the requirement of Poincare invariance (more specifically invariance under boosts/rotations that mix brane directions with transverse directions) places severe constraints on the form of actions describing multiple D-branes, determining an infinite series of correction terms to the currently known actions. For the case of D0-branes, we argue that up to field redefinitions, there is a unique Lorentz transformation rule for the coordinate matrices consistent with the Poincare algebra. We characterize all independent Poincare invariant structures by describing the leading term of each and providing an implicit construction of a Poincare invariant completion. Our construction employs new matrix-valued Lorentz covariant objects built from the coordinate matrices, which transform simply under the (extremely complicated) Lorentz transformation rule for the matrix coordinates. 
Dominic Brecher, Paul Koerber, Henry Ling and Mark Van Raamsdonk