Positivity Properties of the Fourier Transform and the Stability of Periodic Travelling-Wave Solutions

In this paper we establish a method to obtain the stability of periodic travelling-wave solutions for equations of Kortewegde Vries-type $u_t+u^pu_x-Mu_x=0$, with M being a general pseudodifferential operator and where $p\geq1$ is an integer. Our approach uses the theory of totally positive operators, the Poisson summation theorem, and the theory of Jacobi elliptic functions. In particular we obtain the stability of a family of periodic travelling waves solutions for the BenjaminOno equation. The present technique gives a new way to obtain the existence and stability of cnoidal and dnoidal waves solutions associated with the Kortewegde Vries and modified Kortewegde Vries equations, respectively. The theory has prospects for the study of periodic travelling-wave solutions of other partial differential equations.