The cosmological constant, neutrino masses and parity symmetry in 6+1   dimensions
  In this paper we propose that the cosmological constant scale and neutrino masses have a common origin: a new spontaneously broken scalar field. This hypothesis is implemented in a 6-space dimensional model that restores the parity symmetry. The 6-dimensional parity symmetry gives a natural mechanism for the smallness of the vacuum energy density. 
Jos\'e Antonio Martins Sim\~oes