Griffiths singularities in two-dimensional random-bond Ising models: Relation with Lifshitz band tails

Ising models with correlated or uncorrelated random horizontal bonds are studied for square lattices in zero field. The partition sum is expressed in terms of a one-component field. Griffiths singularities in the free energy as function of temperature are derived. They are log-transforms of certain Lifshitz band tails. Griffiths singularities occur above as well as below the critical temperature.