We give the governing equations for multiple scalar fields in a flat Friedmann-Robertson-Walker (FRW) background spacetime on all scales, allowing for metric and field perturbations up to second order. We then derive the Klein-Gordon equation at second order in closed form in terms of gaugeinvariant perturbations of the fields in the uniform curvature gauge. We also give a simplified form of th...

We consider positive, radial and exponentially decaying steady state solutions of the general reaction-diffusion and Klein-Gordon type equations and present an explicit construction of infinite-dimensional invariant manifolds in the vicinity of these solutions. The result is a precise stable manifold theorem for the reaction-diffusion equation and a precise center-stable manifold theorem for th...

We show that every tempered distribution, which is a solution of the (homogenous) Klein-Gordon equation, admits a “tame” restriction to the characteristic (hyper)surface {x0 + x = 0} in (1 + n)-dimensional Minkowski space and is uniquely determined by this restriction. The restriction belongs to the space S′ ∂ − (R) which we have introduced in [16]. Moreover, we show that every element of S′ ∂ ...

The linear and non-linear Klein-Gordon equations are considered. fractional complex transform is used to convert the on a continuous space/time fractals ones Cantor sets, resultant solved by local reduced differential method. Three examples given show effectiveness of technology.