Bound states in the dynamics of a dipole in the presence of a conical   defect
  In this work we investigate the quantum dynamics of an electric dipole in a $(2+1)$-dimensional conical spacetime. For specific conditions, the Schr\"odinger equation is solved and bound states are found with the energy spectrum and eigenfunctions determined. We find that the bound states spectrum extends from minus infinity to zero with a point of accumulation at zero. This unphysical result is fixed when a finite radius for the defect is introduced. 
C. A. de Lima Ribeiro, Claudio Furtado and Fernando Moraes