Parametric superlinear double phase problems with singular term and critical growth on the boundary

In this paper we study quasilinear elliptic equations driven by the double phase operator along with a reaction that has singular and parametric superlinear term nonlinear Neumann boundary condition of critical growth. Based on new equivalent norm for Musielak-Orlicz Sobolev spaces Nehari manifold fibering method prove existence at least two weak solutions provided parameter is sufficiently small.