Particle Masses and the Cosmological 'Constant' in Five Dimensions
  I give metrics and equations of motion in 5D general relativity, and use the conservation of momentum and conformal transformations to study the possible variability of particle masses and the cosmological 'constant'. It is feasible that all particles are photon-like and travel on null paths in 5D, that massive particles are perturbations of the extra dimension which intrude into 4D, and that the cosmological 'constant' is a 5D / 4D gauge term. In the simplest case, a particle has a local cosmological 'constant' whose magnitude is proportional to the square of the mass. 
Paul S. Wesson
gr-qc