Negativity and Concurrence as complete entanglement measures for two   arbitrary qudits
  Two measures of entanglement, negativity and concurrence are studied for two arbitrary qudits. We obtain negativity as an expectation value of an operator. The differences of the squares of negativity and concurrence are invariants of multilevel entanglement. Explicit results for qutrits and quadrits are obtained. 
Suranjana Rai and Jagdish R. Luthra