On the orbital stability of periodic snoidal waves for the ${\phi }^4-$equation

The main purpose of this paper is to investigate the global well-posedness and orbital stability of odd periodic traveling waves for the ${\phi }^4$-equation in the Sobolev space of periodic functions with zero mean. We establish new results on the global well-posedness of weak solutions by combining a semigroup approach with energy estimates. As a consequence, we prove the orbital stability of odd periodic waves by applying a Morse index theorem to the constrained linearized operator defined in the Sobolev space with the zero mean property.