p-Adic and Adelic Free Relativistic Particle
  We consider spectral problem for a free relativistic particle in p-adic and adelic quantum mechanics. In particular, we found p-adic and adelic eigenfunctions. Within adelic approach there exist quantum states that exhibit discrete structure of spacetime at the Planck scale. 
G.S.Djordjevic, B.Dragovich and LJ. Nesic