Wormhole with varying cosmological constant
  It has been suggested that the cosmological constant is a variable dynamical quantity. A class of solution has been presented for the spherically symmetric space time describing wormholes by assuming the erstwhile cosmological constant $\Lambda$ to be a space variable scalar, viz., $\Lambda$ = $\Lambda (r) $ . It is shown that the Averaged Null Energy Condition (ANEC) violating exotic matter can be made arbitrarily small. 
F.Rahaman, M.Kalam, M.Sarker, A.Ghosh and B.Raychaudhuri