Classification of plane-symmetric Lorentzian manifolds according to their homotheties and metrics

Plane-symmetric Lorentzian manifolds are classified according to their homothetic vector fields and metrics or classes of metrics. It is found that these manifolds can admit 4, 5, 7 and 11 dimensional homothetic Lie algebras. Explicit self-similar metrics are obtained corresponding to the homothetic Lie algebras of dimensions greater than or equal to five. For four-dimensional homothetic Lie algebras, there appear classes of self-similar metrics, with metric coefficients related by non-linear differential constraints. Explicit examples are provided to ensure the existence of proper homothetic vector fields in the cases where the metrics are given implicitly. Later, using this classification, self-similar metrics are found which represent perfect-fluid solutions of the Einstein field equations.